Question Bank (Ch. 8)
INTERACTIVE SCIENCE 2A
Question Bank
Chapter 8
MAKING USE OF ELECTRICITY
Concept Checking
Write ‘T’ for a true statement or ‘F’ for a false statement.
8.1
Making Electricity Flow
2A080101Q001Eng
A dry cell stores electrical energy.
[Ans]
F
2A080101Q002Eng
There must be an electricity supply in a complete circuit to light up a bulb in it.
[Ans]
8.2
T
Electrical Conductors and Insulators
2A080101Q003Eng
Insulators stop the electric current from flowing through it.
[Ans]
T
2A080101Q004Eng
All non-metals are electrical insulators.
[Ans]
F
2A080101Q005Eng
The handle of a screwdriver is made of rubber because rubber is a good insulator.
[Ans]
T
2A080101Q006Eng
Only metals conduct electricity.
[Ans]
F
2A080101Q007Eng
All metals conduct electricity.
[Ans]
T
85
Question Bank (Ch. 8)
8.3
Electric Circuit
2A080101Q008Eng
In a closed circuit, free electrons flow from the positive pole of the dry cells towards the negative pole
through the circuit.
[Ans]
T
2A080101Q009Eng
The electric current is measured in volts.
[Ans]
F
2A080201Q010Eng
Metals can conduct electricity because they have many electrons.
[Ans]
F
2A080201Q011Eng
Wood cannot conduct electricity because they have no electrons.
[Ans]
F
2A080101Q012Eng
All electrons in metals always move about a particular nucleus and never move apart.
[Ans]
8.4
F
Voltage
2A080101Q013Eng
A dry cell works as a pump to drive the voltage through the circuit.
[Ans]
F
2A080101Q014Eng
The higher the voltage across a bulb, the greater the electric current flows through the bulb.
[Ans]
T
2A080101Q015Eng
The red terminal of the voltmeter should be connected to the negative pole of the dry cell.
[Ans]
F
2A080101Q016Eng
The methods of connecting an ammeter and connecting a voltmeter in a circuit are the same.
[Ans]
F
2A080101Q017Eng
Several dry cells connected in parallel provides a higher voltage than one dry cell.
[Ans]
F
86
Question Bank (Ch. 8)
8.5
Resistance
2A080101Q018Eng
A rheostat is used to control the electric current in a circuit by changing the length of resistance wire
included in the circuit.
[Ans]
T
2A080101Q019Eng
(extension) A thicker wire has a higher resistance.
[Ans]
F
2A080101Q020Eng
A rheostat provides an adjustable resistance.
[Ans]
T
2A080101Q021Eng
A good electrical conductor has a low resistance.
[Ans]
T
2A080101Q022Eng
Provided other conditions are the same, higher resistance results in a lower current.
[Ans]
T
2A080101Q023Eng
(extension) For wires made of same metals and of same lengths, a thicker wire has larger resistance.
[Ans]
F
2A080101Q024Eng
(extension) For wires made of same metals and of same thickness, longer wire has larger resistance.
[Ans]
T
2A080101Q025Eng
A resistor has a definite value of resistance.
[Ans]
8.6
T
Circuit Symbols
2A080101Q026Eng
Circuit diagrams are diagrams which link up the photographs of different electrical components.
[Ans]
8.7
F
Series and Parallel Circuits
2A080101Q027Eng
The electric current in a series circuit increases as more light bulbs are connected in series to it.
[Ans]
F
87
Question Bank (Ch. 8)
2A080101Q028Eng
The electric current in a series circuit increases as more dry cells are connected in series in it (in proper
direction).
[Ans]
T
2A080101Q029Eng
The size of the electric current flowing through a series circuit is affected by the resistance of the
components connected to it.
[Ans]
T
2A080101Q030Eng
An ammeter must be connected in series to the circuit.
[Ans]
T
2A080101Q031Eng
As the number of branches in a parallel circuit increases, the electric current flowing in the main loop
decreases.
[Ans]
F
2A080101Q032Eng
Removing a bulb from a series circuit will make the circuit open.
[Ans]
T
2A080101Q033Eng
Removing a bulb from one of the branches in a parallel circuit will make the bulbs in all other branches
lights off.
[Ans]
F
8.8
Fuses
2A080101Q034Eng
A circuit breaker is a safety device which switches off the circuit when an excessive electric current flows
through the circuit.
[Ans]
T
2A080101Q035Eng
A fuse wire is a resistance wire which changes electrical energy into heat energy.
[Ans]
T
2A080101Q036Eng
A fuse consists of a short piece of wire with a high melting point installed in a small tube.
[Ans]
F
88
Question Bank (Ch. 8)
2A080101Q037Eng
The amount of heat released from a wire increases with the current flowing through the wire.
[Ans]
T
2A080101Q038Eng
The marking on the surface of a fuse shows the minimum current needed to make it works.
[Ans]
F
2A080101Q039Eng
The fuse rating is the maximum current that can flow through the fuse without burning out.
[Ans]
8.9
T
Household Electricity
2A080101Q040Eng
The earth wire prevents an excessive electric current from flowing through an electrical appliance.
[Ans]
F
2A080101Q041Eng
Both a short circuit and overloading the universal adaptors may lead to fire hazards.
[Ans]
T
2A080101Q042Eng
The fuse in a three-pin plug is connected to the neutral pin.
[Ans]
F
2A080101Q043Eng
The earth wire is connected to the metal case of an electrical appliance.
[Ans]
T
2A080101Q044Eng
The earth wire can protect us from an electric shock.
[Ans]
T
2A080101Q045Eng
Electricity is supplied to our homes from power plants through the live, neutral and earth wires.
[Ans]
F
2A080101Q046Eng
The mains voltage in Hong Kong is 220 V.
[Ans]
T
89
Question Bank (Ch. 8)
2A080101Q047Eng
The three pins in the plug used in Hong Kong are called fire pin, water pin and ground pin.
[Ans]
F
2A080101Q048Eng
The ring circuit provides three paths for electric current to flow from the consumer unit to the mains
sockets.
[Ans]
F
2A080101Q049Eng
The live wire carries a voltage which drives an electric current to flow to the earth wire.
[Ans]
F
2A080101Q050Eng
The earth wire is brown in colour while the live wire is red in colour.
[Ans]
F
2A080101Q051Eng
The fuse is connected to the live wire in a three-pin plug.
[Ans]
T
2A080101Q052Eng
Using electrical appliances with three-pin plugs can protect us from electric shock by earthing when there
is a leakage of electric current.
[Ans]
T
2A080101Q053Eng
The circuit in our home is in series in nature.
[Ans]
F
8.10 Power of an Electrical Appliance
2A080101Q054Eng
(extension) The electric current flowing through an electrical appliance is larger if its power is greater
with the same voltage applied.
[Ans]
8.11
T
Cost of Electricity
2A080101Q055Eng
(extension) 1 kW s stands for one unit of electricity.
[Ans]
F
90
Question Bank (Ch. 8)
2A080101Q056Eng
A bulb with higher power consumes more electrical energy than another bulb with lower power within
the same time span.
[Ans]
8.12
T
Working Principles of Common Electrical Appliances
2A080101Q057Eng
(extension) A toaster makes use of the heating effect of an electric current.
[Ans]
T
2A080101Q058Eng
(extension) Electric appliances which make use of the magnetic effect of an electric current have a
component of plastic coils.
[Ans]
F
2A080101Q059Eng
Heating effect and magnetic effect of an electric current are two major principles of how electrical
appliances work.
[Ans]
T
2A080101Q060Eng
Electric motor is one of the examples of making use of heating effect of electric current.
[Ans]
F
Multiple Choice
Circle the best answer for each question below.
8.1
Making Electricity Flow
2A080102Q001Eng
Which of the following components are needed to build a circuit that can light up a bulb?
(I)
Switchs
(II)
Dry cells
(III)
Connecting wires
A.
(II) only
B.
(I) and (II) only
C.
(II) and (III) only
D.
All of the above
[Ans]
C
91
Question Bank (Ch. 8)
2A080102Q002Eng
A complete circuit can also be called a/an ______________ .
A.
on circuit
B.
off circuit
C.
open circuit
D.
closed circuit
[Ans]
8.2
D
Electrical Conductors and Insulators
2A080102Q003Eng
Which of the following statements about these substances is true?
graphite, plastic, gold, iron
A.
All of them are conductors.
B.
All of them are insulators.
C.
Only graphite and plastic are insulators.
D.
Only graphite, gold and iron are conductors.
[Ans]
D
2A080102Q004Eng
Which of the following objects is/are conductor(s)?
(I)
Nichrome wire
A.
(I) only
B.
(I) and (III) only
C.
(II), (III) and (IV) only
D.
(I), (III) and (IV) only
[Ans]
(II)
Plastic ruler
(III)
Graphite rod
D
2A080102Q005Eng
Which of the following is a function of a switch?
A.
To break a circuit
B.
To supply electrical energy
C.
To control the melting point of a bulb
D.
To protect a bulb from excess current
[Ans]
A
2A080102Q006Eng
Which of the following is the common characteristic of insulators?
A.
Insulators are non-metals.
B.
Insulators have no electrons.
C.
Insulators have free atoms.
D.
Insulators do not allow electric current to flow through.
[Ans]
D
92
(IV)
Silver ring
Question Bank (Ch. 8)
8.3
Electric Current
2A080102Q007Eng
An electric current is measured in ___________ .
A.
volts
B.
amperes
C.
ohms
D.
pascals
[Ans]
B
2A080102Q008Eng
The negative terminal of an ammeter is always coloured ________ .
A.
brown
B.
red
C.
black
D.
blue
[Ans]
C
8.4
Voltage
2A080202Q009Eng
Which of the following conditions gives the greatest voltage across each bulb when the following
components are connected in series?
A.
five identical dry cells and five identical light bulbs
B.
five identical dry cells and two identical light bulbs
C.
two identical dry cells and five identical light bulbs
D.
two identical dry cells and two identical light bulbs
[Ans]
B
2A080102Q010Eng
In order to measure the voltage of a battery, the red pole of a voltmeter should be connected to
A.
the black pole of the voltmeter.
B.
the red pole of the voltmeter.
C.
the negative pole of the battery.
D.
the positive pole of the battery.
[Ans]
D
93
Question Bank (Ch. 8)
2A080102Q011Eng
Refer to the circuit diagram below, what the devices X and Y should be?
Y
X
X
Y
A.
Voltmeter
Ammeter
B.
Ammeter
Voltmeter
C.
Ammeter
Ammeter
D.
Voltmeter
Voltmeter
[Ans]
B
2A080102Q012Eng
Refer to the circuit diagram below,
Y
X
Component X is a device that measures _________________ .
A.
current
B.
voltage
C.
resistance
D.
power
[Ans]
8.5
A
Resistance
2A080102Q013Eng
Which of the following are parts of a sliding rheostat?
(I)
Sliding contact
A.
(I) and (III) only
B.
(I), (II) and (III) only
C.
(I), (III) and (IV) only
D.
(I), (II), (III) and (IV)
[Ans]
(II)
Fuse
(III)
C
94
Resistance wire
(IV)
Connecting terminal
Question Bank (Ch. 8)
2A080202Q014Eng
(extension) The following wires are made of the same material. Which one has the highest resistance?
[Ans]
A.
B.
C.
D.
C
2A080102Q015Eng
The rheostat in the circuit below can be used to change ______________________ .
A.
the melting point of the filament in the bulb
B.
the electric current flowing through the bulb
C.
the resistance of the bulb
D.
the voltage of the dry cell
[Ans]
B
2A080102Q016Eng
Which of the following best describes a rheostat?
A.
A resistor with variable resistance
B.
A wire with variable voltage
C.
A switch with variable size
D.
A dry cell with variable current
[Ans]
A
2A080102Q017Eng
(extension) Which of the following changes can increase the resistance of a wire?
A.
Increase the thickness of the metal core of the wire
B.
Increase the thickness of the insulator layer of the wire
C.
Reduce the thickness of the metal core of the wire
D.
Reduce the thickness of the insulator layer of the wire
[Ans]
C
95
Question Bank (Ch. 8)
8.6
Circuit Symbols
2A080102Q018Eng
What does the following symbol represent?
A.
A dry cell
B.
An ammeter
C.
A rheostat
D.
A voltmeter
[Ans]
C
2A080102Q019Eng
Which of the following is the correct symbol of a dry cell?
A.
B.
C.
D.
[Ans]
8.7
B
Series and Parallel Circuits
2A080102Q020Eng
Which of the following statements about a parallel circuit is/are correct?
(I)
The electric current is the same at all the points in the circuit.
(II)
The electric current in the main loop is equal to the sum of the currents in the branches.
(III)
When the bulb on the first branch burns out, the other bulbs still light up.
A.
(II) only
B.
(I) and (II) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
C
2A080102Q021Eng
Three ammeters are connected in series with a dry cell and two light bulbs. Which of the following
statements about this circuit is/are correct?
(I)
All the ammeter readings are equal.
(II)
The ammeter nearest the dry cell has the highest reading.
(III)
The ammeter between the two bulbs reads zero.
96
Question Bank (Ch. 8)
A.
(I) only
B.
(II) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
A
2A080202Q022Eng
John has three identical bulbs. He first connects two bulbs in parallel as a group, and the group in turns to
a battery. Now, he adds one more bulbs so that the three bulbs are in parallel. Which of the following
about the bulbs is correct?
A.
They are equally bright.
B.
The middle one is the brightest.
C.
The first two are brighter than the last one.
D.
The resistance is now so high that no electric current can flow through the circuit.
[Ans]
A
2A080102Q023Eng
Which of the following statements about a series circuit is correct?
A.
The electric current is the same at every point in the circuit.
B.
There is still an electric current flowing through the circuit even if one of the components in the
circuit is broken.
C.
The size of the electric current drops along the circuit.
D.
The electric current in the circuit increases with the number of components connected.
[Ans]
A
2A080102Q024Eng
What is the advantage of a parallel circuit over a series circuit?
A.
All electric appliances draw equal amount of electric current.
B.
Each electric appliance could be switched off without affecting others.
C.
It is cheaper to build.
D.
It is simpler to build.
[Ans]
B
97
Question Bank (Ch. 8)
2A080202Q025Eng
Which of the following circuits is a series circuit?
A.
B.
C.
D.
[Ans]
C
8.8
Fuses
2A080102Q026Eng
To protect an electrical appliance from being damaged by a very large electric current, we put a/an
_________________ in the circuit.
A.
rheostat
B.
ammeter
C.
nichrome wire
D.
fuse
[Ans]
D
2A080102Q027Eng
Which of the following fuse ratings is the best for an air conditioner with the working current of
11 A?
A.
13 A
B.
5A
C.
3A
D.
1A
[Ans]
A
2A080102Q028Eng
Which of the following conditions may lead to a very large electric current in the main path?
(I)
A short circuit
(II)
A lot of bulbs connected in parallel
(III)
A lot of bulbs connected in series
(IV)
A lot of dry cells connected in series
98
Question Bank (Ch. 8)
A.
(I) and (II) only
B.
(III) and (IV) only
C.
(I), (II) and (IV) only
D.
(II), (III) and (IV) only
[Ans]
C
2A080102Q029Eng
The function of a circuit breaker is
A.
to close a circuit when the current exceeds its rating.
B.
to close a circuit when the voltage is too high.
C.
to open a circuit when the current exceeds it rating.
D.
to open a circuit when the power is too large.
[Ans]
C
2A080102Q030Eng
The marking of ‘5 A’ on a fuse means
A.
that it can only let 5 A current to pass through.
B.
that current higher than 5 A breaks the fuse.
C.
that the minimum current to pass through is 5 A.
D.
a brand name called ‘5 A’.
[Ans]
C
2A080102Q031Eng
What is the circuit symbol of a fuse?
A.
B.
C.
D.
[Ans]
8.9
C
Household Electricity
2A080102Q032Eng
When a person is having an electric shock, what should be done immediately to save him?
A.
Pull him away from the wire with bare hands.
B.
Call the police.
C.
Ask for help loudly.
D.
Switch off the main switch.
[Ans]
D
99
Question Bank (Ch. 8)
2A080202Q033Eng
A fuse is connected to the live wire of the circuit. Which of the following statements is/are the key
reason(s)?
(I)
Fuse is made of a low resistance wire, and can reduce the power loss.
(II)
Once the fuse burns out, no electric current will flow through the electrical appliance.
(III)
In case of an electric fault, the leaking current will flow through the neutral wire.
A.
(I) only
B.
(II) only
C.
(I) and (II) only.
D.
(II) and (III) only
[Ans]
B
2A080102Q034Eng
An electric plug is shown below. What is the use of part X in the plug?
X
A.
To cut off the electric current if it is too large.
B.
To show the size of the electric current.
C.
To stop the electric current in the plug.
D.
To enlarge the electric current in the wires.
[Ans]
A
2A080102Q035Eng
Which of the following combinations correctly shows the colour of wires in electrical appliances?
Live
Neutral
Earth
A.
Brown
Blue
Green and yellow
B.
Blue
Brown
Green and yellow
C.
Green and yellow
Brown
Blue
D.
Green and yellow
Blue
Brown
[Ans]
B
2A080102Q036Eng
Which of the following actions is dangerous?
A.
Switch off the power before removing the plug from the mains socket.
B.
Replace a blown fuse with a copper wire of the same thickness.
C.
Dry the hands before switching on any electrical appliance at home.
D.
Disconnect the table lamp before replacing the blown bulb.
[Ans]
B
100
Question Bank (Ch. 8)
2A080102Q037Eng
Which of the following statements correctly explain why we should not connect too many electrical
appliances to one mains socket at the same time by using universal adaptors?
A.
The electric current may be so large that this may cause a fire.
B.
The electric current may not be enough for too many electrical appliances to work together.
C.
The electric current may be broken if one of the electrical appliances is damaged.
D.
The electric current will not flow through every electrical appliance.
[Ans]
A
2A080102Q038Eng
What will happen if the earth wire of an electric appliance is disconnected?
(I)
No electricity will be supplied to the electrical appliance.
(II)
You may get an electric shock if you touch the electrical appliance.
(III)
A short circuit may result.
A.
(I) only
B.
(II) only
C.
(I) and (II) only
D.
(II) and (III) only
[Ans]
B
2A080102Q039Eng
The main voltage in Hong Kong is _________ .
A.
5V
B.
12 V
C.
110 V
D.
220 V
[Ans]
D
2A080102Q040Eng
A ring circuit is a kind of ___________ .
A.
open circuits
B.
parallel circuits
C.
series circuits
D.
DC circuits
[Ans]
B
101
Question Bank (Ch. 8)
2A080102Q041Eng
The colour of live wire is ___________ .
A.
blue
B.
green
C.
black
D.
brown
[Ans]
D
2A080102Q042Eng
The earth wire is connected to
A.
the fuse inside the socket.
B.
the neutral wire.
C.
the live wire.
D.
the case of an electric appliance.
[Ans]
D
2A080102Q043Eng
A fuse should be installed
A.
at the live pin.
B.
at the neutral pin.
C.
at the earth pin.
D.
inside the circuit breaker.
[Ans]
A
2A080102Q044Eng
An electric plug is shown below. What are R, S and T respectively?
T
R
S
R
S
T
A.
Netrual
Live
Earth
B
Live
Earth
Neutral
C.
Earth
Neutral
Live
D.
Earth
Live
Neutral
[Ans]
C
102
Question Bank (Ch. 8)
2A080102Q045Eng
There are three holes in the mains socket. The bottom left hole is ________ .
A.
the neutral socket
B.
the earth socket
C.
the live socket
D.
the water socket
[Ans]
A
2A080102Q046Eng
Short circuit should be avoided because
A.
it costs a lot in the bill.
B.
it wastes energy.
C.
it is short.
D.
it may lead to great heating effect and cause a fire.
[Ans]
D
2A080202Q047Eng
Which of the following circuit is a short circuit?
A.
B.
C.
D.
[Ans]
C
2A080102Q048Eng
Which of the followings is/are the safety design(s) of an electrical appliance?
(I)
Installing a fuse in the appliance
(II)
Connecting the earth pin to the case
(III)
Handles made of rubber or plastic
103
Question Bank (Ch. 8)
A.
(II) only
B.
(I) and (II) only
C.
(II) and (III) only
D.
All of the above
[Ans]
C
2A080102Q049Eng
Using an plug with two pins only is dangerous because
A.
We will get an electric shock if there is a leaking.
B.
The house will catch a fire easily.
C.
There will be no space to install a fuse.
D.
The current will be very large.
[Ans]
A
2A080102Q050Eng
Which of the followings may lead to a fire in house?
(I)
Overloading
(II)
Short circuit
(II)
Burning of fuse
A.
(II) only
B.
(I) and (II) only
C.
(II) and (III) only
D.
All of the above
[Ans]
B
2A080102Q051Eng
Which of the following devices is/are used to prevent excessive current in the circuit?
(I)
Fuse
(II)
Circuit breaker
(III)
Earth wire
A.
(II) only
B.
(I) and (II) only
C.
(II) and (III) only
D.
All of the above
[Ans]
B
104
Question Bank (Ch. 8)
8.10 Power of an Electrical Appliance
2A080102Q052Eng
(extension) Refer to the circuit diagram below, the readings of devices M and N are 0.1 unit and 1.5 units
respectively. What is the power of the bulb?
A.
0.067 unit
B.
0.15 unit
C.
1.5 units
D.
15 units
[Ans]
8.11
B
Cost of Electricity
2A080102Q053Eng
(extension) Which of the following instruments is used to measure the amount of electrical energy
consumed?
A.
An ammeter
B.
A kilowatt-hour meter
C.
A voltmeter
D.
A fuse
[Ans]
B
2A080102Q054Eng
(extension) An electric heater with a power of 2000 W has been operated for 4 hours. Supposed the cost
of 1 unit of electricity is $0.6. Calculate the total cost of electricity used for these 4 hours.
A.
$0.6
B.
$1.2
C.
$2.4
D.
$4.8
[Ans]
D
105
Question Bank (Ch. 8)
2A080102Q055Eng
(extension) The following data are extracted from David’s electricity bill. The unit cost of electricity is
$0.9. How much should David pay?
A.
$180
B.
$222
C.
$3780
D.
$4667
[Ans]
Present meter reading
Previous meter reading
57893
53693
C
2A080102Q056Eng
The unit of electrical energy consumed is
A.
V
B.
W
C.
kV h
D.
kW h
[Ans]
D
2A080202Q057Eng
A 20 W power-saving bulb has worked for 2 days. How many units of electricity have been used?
A.
0.96
B.
0.04
C.
960
D.
100
[Ans]
A
2A080202Q058Eng
(extension) There is a marking “200 V, 5 A” on the surface on a bulb. How many units of electricity are
consumed by the bulb to operate for 4 hours?
A.
1000
B.
800
C.
20
D.
4
[Ans]
D
106
Question Bank (Ch. 8)
8.12
Working Principles of Common Electrical Appliances
2A080102Q059Eng
(extension) Which of the following electrical appliances makes use of the magnetic effect of an electric
current?
A.
A telephone earpiece
B.
An electric oven
C.
An electric iron
D.
A computer
[Ans]
A
2A080202Q060Eng
(extension) Which of the following are the conditions for a current-carrying rod to move?
currentcarrying
rod
(I)
Electric current
A.
(I) and (II) only
B.
(II) and (III) only
C.
(I) and (III) only
D.
(I), (II) and (III)
[Ans]
(II)
magnets
Magnetic force
(III)
Resistance
A
2A080102Q061Eng
Which of the following effects are induced by an electric current?
(I)
Sounding effect
(II)
Heating effect
(III)
Magnetic effect
A.
(II) only
B.
(I) and (II) only
C.
(II) and (III) only
D.
All of the above
[Ans]
C
107
Question Bank (Ch. 8)
2A080102Q062Eng
The coil in the circuit diagram below is made of iron. What will happen to coil when the circuit is closed?
A.
It attracts paper scraps.
B.
It heats up.
C.
It lights up.
D.
Nothing will happen.
[Ans]
B
Fill in the Blanks
8.1
Making Electricity Flow
2A080103Q001Eng
If an electrical current flows in a circuit, the circuit must be a/an (a)_____________ circuit with a source
of electrical (b)_____________ .
[Ans]
(a) closed
(b) energy
2A080103Q002Eng
To light up a bulb, we have to connect it to a/an (a)_____________ circuit with a/an (b)_____________
supply.
[Ans]
(a) closed
(b) energy
2A080103Q003Eng
One of the common energy sources that we usually use on circuit boards is _____________ .
[Ans]
8.2
dry cells
Electrical Conductors and Insulators
2A080103Q004Eng
Electrical (a)_____________ allow electric current to flow through while electrical (b)_____________ do
not.
[Ans]
(a) conductors
(b) insulators
2A080103Q005Eng
_____________ is a form of carbon; it is a non-metal but it also conducts electricity.
[Ans]
Graphite
108
Question Bank (Ch. 8)
2A080103Q006Eng
Generally, metals are electrical (a)_____________ conductors while non-metals are electrical
(b)_____________ .
[Ans]
(a) conductors
(b) insulators
2A080103Q007Eng
A _____________ is a device which opens or closes a circuit.
[Ans]
8.3
switch
Electric Circuit
2A080103Q008Eng
An electric _____________ in metal is the flow of free electrons.
[Ans]
current
2A080103Q009Eng
In a circuit, the free electrons move from the (a)_____________ pole of the battery to the
(b)_____________ pole along the connecting wires.
[Ans]
(a) negative
(b) positive
2A080103Q010Eng
All matters on Earth are made by atoms, which is composed with a positively charged (a)_____________
and negatively charged (b)_____________ .
[Ans]
(a) nucleus
(b) electrons
2A080103Q011Eng
A/An (a)_____________is an instrument to measure the size of an electric current. The electric current is
measured in (b)_____________ with symbol (c)_____________ .
[Ans]
(a) ammeter
(b) ampere
(c) A
2A080103Q012Eng
The red terminal of an ammeter should connect to the side towards the (a)_____________ pole of the dry
cell while the black terminal to the side towards the (b)_____________ pole.
[Ans]
8.4
(a) positive
(b) negative
Voltage
2A080103Q013Eng
A dry cell of 3 V provides a higher _____________ to drive electrons to flow through the circuit in a
definite direction than a dry cell of 1.5 V.
[Ans]
voltage
109
Question Bank (Ch. 8)
2A080103Q014Eng
A/An (a)_____________ is an instrument to measure the voltage, normally the voltage of a dry cell. The
unit of voltage is (b)_____________ and the symbol is (c)_____________ .
[Ans]
(a) voltmeter
(b) volt
(c) V
2A080103Q015Eng
In order to get 4.5 V with three 1.5V dry cells, the (a)_____________ pole of one cell should connect to
the (b)_____________ pole of another.
[Ans]
(a) positive
(b) negative
2A080103Q016Eng
When we measure the voltage of a dry cell, we should connect the red terminal of a voltmeter to the
(a)_____________ pole of dry cell and the black terminal to the (b)_____________ pole.
[Ans]
8.5
(a) positive
(b) negative
Resistance
2A080103Q017Eng
The size of the electric current flowing in a circuit is affected by the _____________ of the electrical
conductors connected to it.
[Ans]
resistance
2A080103Q018Eng
A sliding (a)_____________ is used to control the size of the electric (b)_____________ flowing through
a circuit. It changes the resistance by changing the (c)_____________ of the resistance wire connected to
the circuit.
[Ans]
(a) rheostat
(b) electric current
(c) length
2A080103Q019Eng
(extension) A long, thin wire has a higher _____________ than a short, thick wire of the same material.
[Ans]
resistance
2A080103Q020Eng
(extension) The resistance of a wire is determined by its (a)_____________ , (b)_____________ and
(c)_____________ .
[Ans]
(a) material
(b) length
(c) thickness
2A080103Q021Eng
(a)_____________ are devices of a specific resistance, often having their values shown by the colour
(b)_____________ printed on their surfaces.
[Ans]
(a) Resistors
(b) codes/bars
110
Question Bank (Ch. 8)
2A080103Q022Eng
A resistor with variable resistance is also called a/an _____________ . It can be used to change the size of
current without changing the voltage.
[Ans]
8.6
rheostat
Circuit Symbols
2A080103Q023Eng
A kind of simple drawing called a/an (a)_____________ is used to show the connections between
electrical components by symbols. A straight line in it represents (b)_____________ .
[Ans]
(a) circuit diagram (b) wires/connectors
2A080103Q024Eng
The dry cell is an important electrical component. Its circuit symbol consists of two lines. The longer,
thinner line represents the (a)_____________ pole while the shorter, thicker line represents the
(b)_____________ pole.
[Ans]
8.7
(a) positive
(b) negative
Series and Parallel Circuits
2A080103Q025Eng
An ammeter is connected in (a)_____________ to the component to measure the electric current through
the component. Current is measured in (b)_____________ (symbol A) or (c)_____________ (symbol
mA).
[Ans]
(a) series
(b) amperes
(c) milliamperes
2A080103Q026Eng
The electric current is the same at all points in a _____________ circuit.
[Ans]
series
2A080103Q027Eng
In a _____________ circuit, there are many branches through which the electric current can flow.
[Ans]
parallel
2A080103Q028Eng
In a _____________ circuit, all bulbs are connected one by one and the current flows through a single
path.
[Ans]
series
2A080103Q029Eng
In a _____________ circuit, the bulbs are connected in different branches. The current flows through
more than one path.
[Ans]
parallel
111
Question Bank (Ch. 8)
2A080103Q030Eng
In a parallel circuit, the _____________ through the main path is equal to the sum of those through each
branch.
[Ans]
current
2A080103Q031Eng
Remove a bulb from circuit X will break the circuit. Therefore, no current can flow and all other devices
on the circuit are off. Therefore, circuit X is a _____________ circuit.
[Ans]
series
2A080103Q032Eng
Remove a bulb from a branch of circuit Y will break the branch. No current can flow through the branch
and all devices connected in that branch are off. However, current can still flow through other branches .
Devices on the other branches are not be affected. Therefore, circuit Y is a _____________ circuit.
[Ans]
8.8
parallel
Fuses
2A080103Q033Eng
Besides a circuit breaker, a _____________ is also a safety device that will break the circuit if the electric
current increases above a certain value.
[Ans]
fuse
2A080103Q034Eng
A fuse consists of a short piece of wire with a low _____________ point installed in a tube.
[Ans]
melting
2A080103Q035Eng
The _____________ of a fuse indicates the maximum electric current it can withstand without burning out.
[Ans]
rating (fuse rating)
2A080103Q036Eng
Replacing a blown fuse is quite trouble. In modern buildings, _____________ are used instead.
[Ans]
circuit breakers
2A080103Q037Eng
When electric current flows through a wire, part of the energy changes into (a)_____________ energy.
When the electric current increases, the temperature of the wire (b)_____________ .
[Ans]
(a) heat
(b) increases
2A080103Q038Eng
A/An (a)_____________ is similar to the fuse. If the current is (b)_____________ than the rating, it will
turn to “off” position and (c)_____________ the circuit
[Ans]
(a) circuit breaker
(b) higher
(c) breaks
112
Question Bank (Ch. 8)
8.9
Household Electricity
2A080103Q039Eng
The three holes in a mains socket are called the (a)_____________ socket, the (b)_____________ socket
and the (c)_____________ socket.
[Ans]
(a) live
(b) neutral
(c) earth
2A080103Q040Eng
In a three-pin plug, the colour of the (a)_____________ wire is brown, that of the (b)_____________
wire is blue and that of the (c)_____________ wire is green and yellow.
[Ans]
(a) live
(b) neutral
(c) earth
2A080103Q041Eng
In our homes, all main sockets are connected to a circuit that provides two paths for the electric current to
pass from the mains supply to the mains sockets. Such circuit is called a _____________ circuit.
[Ans]
ring
2A080103Q042Eng
If the case of an electrical appliance is made of (a)_____________ , the (b)_____________ wire should
be connected to the case of the electrical appliance.
[Ans]
(a) metal
(b) earth
2A080103Q043Eng
The switch and the fuse are connected to the _____________ wire of an electrical appliance.
[Ans]
live
2A080103Q044Eng
Without an (a)_____________ wire in an electrical appliance, a leaking electric current may pass through
our body and we may get an electric (b) _____________ when we touch the electrical appliance.
[Ans]
(a) earth
(b) shock
2A080103Q045Eng
To use electricity safely, we must avoid (a)_____________ the circuit by connecting too many electrical
appliances to a socket with a universal (b)_____________ . We should also replace wires which have
been using for more than ten years in order to avoid a/an (c)_____________ circuit.
[Ans]
(a) overloading
(b) adaptor
2A080103Q046Eng
The main voltage in Hong Kong is (a)_____________ V while that in the USA is (b)_____________ V.
[Ans]
(a) 220
(b) 110
113
Question Bank (Ch. 8)
2A080103Q047Eng
The circuit in our home is a/an (a)_____________ circuit. Breakage of one appliance will not affect the
others. Therefore, it is a kind of (b)_____________ circuit.
[Ans]
(a) ring
(b) parallel
2A080103Q048Eng
Ring circuit provides two paths for each wire to reduce the chance of _____________ that makes the
wires overheat.
[Ans]
overloading
8.10 Power of an Electrical Appliance
2A080103Q049Eng
(extension) The (a)_____________ of an electrical appliance is the amount of electrical energy consumed
per second. It is measured in (b)_____________ (symbol W) or (c)_____________ (symbol kW).
[Ans]
(a) power
(b) watts
(c) kilowatts
2A080103Q050Eng
(extension) The size of an electric current flowing through an electrical appliance is equal to its
(a)_____________ divided by the (b)_____________ applied.
[Ans]
(a) power
(b) voltage
2A080103Q051Eng
(extension) The amount of electrical energy used by an electrical appliance is equal to its
(a)_____________ multiplied by the (b)_____________ of operation.
[Ans]
(a) power
(b) time
2A080103Q052Eng
(extension) In our homes, _____________ are used to measure the amount of electrical energy consumed.
[Ans]
kilowatt-hour meters
2A080103Q053Eng
(extension) The amount of electrical energy used in one second is called (a)_____________ . It is
measured in (b)_____________ with the symbol W. 1 unit of electricity is 1 (c)_____________ .
[Ans]
(a) power
(b) watts
(c) KW h
2A080103Q054Eng
(extension) Normally, A bulb of higher power consumes (a) _____________ energy and has
(b)_____________ brightness than that of lower power when the bulbs are compared in the same period
of time.
[Ans]
(a) more
(b) higher
114
Question Bank (Ch. 8)
8.12
Working Principles of Common Electrical Appliances
2A080103Q055Eng
(extension) Electrical heaters make use of the (a)_____________ effect of an electric current. The heating
elements in them are usually resistance wires in a shape of a/an (b)_____________ .
[Ans]
(a) heating
(b) coil
2A080103Q056Eng
(extension) A/An (a)_____________ is a coil which behaves like a magnet when an electric
(b)_____________ flows through it.
[Ans]
(a) electromagnet
(b) electric current
2A080103Q057Eng
(extension) Some electrical appliances make use of the (a)_____________ effect of an electric current.
They may contain electromagnets or (b)_____________ .
[Ans]
(a) magnetic
(b) motors
2A080103Q058Eng
(extension) The working principle of most of the electrical appliances is based on the two effects of a
current. They are (a)_____________ effect and (b)_____________ effect.
[Ans]
(a) heating
(b) magnetic
2A080103Q059Eng
(extension) An electric iron use the (a)_____________ effect of a current while a motor use the
(b)_____________ effect of an electric current.
[Ans]
(a) heating
(b) magnetic
2A080103Q060Eng
A magnetic _____________ is produced on a current-carrying conductor when the conductor is placed
near a magnet.
[Ans]
force
Short Questions
8.1
Making Electricity Flow
2A080104Q001Eng
What is the energy change in a dry cell when it is connected to a closed circuit?
________________________________________________________________________________
[Ans]
Energy changes from chemical energy to electrical energy.
115
Question Bank (Ch. 8)
2A080104Q002Eng
What are the TWO conditions that allows an electric current to flow?
_________________________________________________________________________________
[Ans]
There should be an electricity supply (e.g. a dry cell) and a complete path for the electricity to flow.
8.2
Electrical Conductors and Insulators
2A080104Q003Eng
The diagram below shows a wire.
rubber cover
(a)
thin metal wires
Explain why the thin metal wires are covered with a rubber cover.
___________________________________________________________________________
(b)
What is the function of the thin metal wires?
___________________________________________________________________________
[Ans]
(a)
Rubber is an electrical insulator. It protects us from an electric shock.
(b)
They are electrical conductors and are used to conduct electricity.
2A080104Q004Eng
Peter: “All non-metals are insulators.”
Mary: “No, copper is a non-metal but it is a good conductor. ”
(a)
Comment on their statements by pointing out whether they are correct and briefly explain your
answer.
___________________________________________________________________________
(b)
What makes metal a good conductor?
___________________________________________________________________________
[Ans]
(a)
Both are incorrect. Graphite is a non-metal that conducts electricity. Copper is a good conductor
but it is a metal.
(b)
Metal has a lot of free electrons that can flow from one atom to another.
2A080104Q005Eng
(a)
What are conductors and insulators?
___________________________________________________________________________
___________________________________________________________________________
(b)
Why is the handle of tools used in electrical technicians made by rubber?
___________________________________________________________________________
___________________________________________________________________________
[Ans]
(a)
Conductors are substances that allow electricity to pass through while insulators do not.
(b)
Since rubber is an insulator, it can protect the technicians from an electric shock if there is a
leakage accidentally.
116
Question Bank (Ch. 8)
8.3
Electric Circuit
2A080104Q006Eng
The diagram below shows an ammeter connected to a circuit.
ammeter
(a)
Consider the ammeter.
(i)
What does the ammeter measure?
_____________________________________________________________________
(ii)
What is the unit of measurement?
_____________________________________________________________________
(b)
In the above diagram, use arrows to show the flow of the free electrons in the circuit.
[Ans]
(a)
(i) The size of an electric current
(ii) Ampere or milliampere
(b)
ammeter
Negative pole of the dry cells circuit outside the dry cells  positive pole of the dry cells
2A080104Q007Eng
What does an atom consist of?
________________________________________________________________________________
[Ans]
An atom consists of a positively charged nucleus surrounded by tiny, negatively charged electrons.
2A080104Q008Eng
What is the major difference between free electrons and “non-free” electrons under electrical energy
supply?
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
117
Question Bank (Ch. 8)
[Ans]
Free electrons are electrons that are able to flow from one atom to another while non-free electrons
surround a particular nucleus. When there is an electrical energy supply, the free electrons are driven to
flow in the same direction and thus electric current is formed.
8.4
Voltage
2A080104Q009Eng
The diagram below shows a voltmeter connected to a circuit.
voltmeter
(a)
(i)
What does a voltmeter measure?
_____________________________________________________________________
(ii)
What is the unit of measurement?
_____________________________________________________________________
(b)
If the number of the dry cells is increased to three (in proper direction), what will happen to
(i)
the reading of the voltmeter?
_____________________________________________________________________
(ii)
the size of the electric current?
_____________________________________________________________________
[Ans]
(a)
(i) Voltage
(ii) Volt
(b)
(i) It will increase.
(ii) It will increase.
2A080104Q010Eng
Why is a torch with 3 dry cells brighter than that with 2 dry cells?
________________________________________________________________________________
________________________________________________________________________________
[Ans]
It is because 3 dry cells provide a larger voltage and thus gives a larger current. A larger current gives
higher brightness.
118
Question Bank (Ch. 8)
8.5
Resistance
2A080204Q011Eng
The diagram below shows a set-up used to study the resistance of two wires, X and Y.
wire X or Y
(a)
(i)
What is the unit of resistance?
_____________________________________________________________________
(ii)
(b)
What is its symbol?
If wire Y has a higher resistance than wire X, compare the following when they are used in the
circuit:
(i)
the size of the electric current
_____________________________________________________________________
(ii)
the brightness of the bulb
_____________________________________________________________________
[Ans]
(a)
(i) Ohm
(ii) 
(b)
(i) The electric current is greater when wire X is used.
(ii) The bulb is brighter when wire X is used.
2A080204Q012Eng
(extension) The table below compares three types of wires.
Wire A
Wire B
Wire C
Length (cm)
20
15
20
Thickness (mm)
5
5
3
copper
copper
nichrome
Material
(a)
Which material is a better conductor, nichrome or copper?
___________________________________________________________________________
(b)
(extension) Which wire has the lowest resistance? Briefly explain.
___________________________________________________________________________
___________________________________________________________________________
119
Question Bank (Ch. 8)
[Ans]
(a)
Copper
(b)
Wire B, because it is shorter than wire A and B and thicker than wire C and it is made of copper,
which is a better conductor than nichrome.
2A080104Q013Eng
The diagram below shows a rheostat connected in a circuit.
rheostat
.
(a)
What is the function of a rheostat?
___________________________________________________________________________
(b)
If the resistance of the rheostat decreases, what will happen to
(i)
the brightness of the bulb?
_____________________________________________________________________
(ii)
the reading of the ammeter?
_____________________________________________________________________
(c)
What is the circuit symbol for a rheostat?
[Ans]
(a)
It varies the size of an electric current flowing through a circuit.
(b)
(i) The bulb will be brighter.
(ii) The reading will increase.
(c)
2A080104Q014Eng
Normally, we use a copper wire to connect a bulb to a dry cell.
(a)
If the copper wire is replaced by a nichrome wire, what will happen to the bulb?
___________________________________________________________________________
(b)
How does the resistance relate to the brightness of a bulb?
___________________________________________________________________________
___________________________________________________________________________
120
Question Bank (Ch. 8)
[Ans]
(a)
The bulb becomes dimmer.
(b)
The resistance of a nichrome wire is higher than that of a copper wire. Higher resistance results in
lower current. The brightness thus decreases.
8.6
Circuit Symbols
2A080104Q015Eng
Draw the circuit symbols of the following components:
(a)
A bulb
(b)
A switch
(c)
A resistor
[Ans]
(a)
(b)
(c)
121
Question Bank (Ch. 8)
2A080104Q016Eng
Draw the circuit diagrams for the following:
(a)
(b)
[Ans]
(a)
(b)
122
Question Bank (Ch. 8)
8.7
Series and Parallel Circuits
2A080104Q017Eng
The diagram below shows two types of circuit.
circuit A
(a)
circuit B
What is the name for the type of circuit in
(i)
circuit A?
_____________________________________________________________________
(ii)
circuit B?
_____________________________________________________________________
(b)
In which circuit are the bulbs brighter?
___________________________________________________________________________
(c)
What happens to the bulbs in these circuits if one of the bulbs in each circuit is removed?
___________________________________________________________________________
___________________________________________________________________________
[Ans]
(a)
(i) Series circuit
(ii) Parallel circuit
(b)
Circuit B
(c)
In circuit A, other bulbs go out. In circuit B, other bulbs remain unaffected.
2A080204Q018Eng
The diagram below shows a circuit. The bulbs are identical.
X
Y
(a)
A2
Z
A1
A3
Compare the brightness between
(i)
bulbs Y and Z.
_____________________________________________________________________
(ii)
bulbs X and Z.
_____________________________________________________________________
123
Question Bank (Ch. 8)
(b)
Compare the readings between ammeter A1 and A2.
___________________________________________________________________________
___________________________________________________________________________
[Ans]
(a)
(i) Their brightness is the same.
(ii) Bulb X is brighter.
(b)
The reading of A1 is greater than that of A2.
2A080104Q019Eng
What is the major difference between a series and a parallel circuit?
________________________________________________________________________________
________________________________________________________________________________
[Ans]
There is only one path for the electrons to flow in a series circuit. In a parallel circuit, there are more than
one branches.
2A080104Q020Eng
Give ONE advantage of a parallel circuit over a series circuit.
________________________________________________________________________________
[Ans]
If one of the electric appliances is broken, others will not be affected.
2A080204Q021Eng
According to the circuit below,
R
S
(a)
P
T
Q
What will happen to the bulbs when the switch P is closed?
___________________________________________________________________________
(b)
What will happen to bulb R when both switches P and Q are closed?
___________________________________________________________________________
[Ans]
(a)
Bulb R lights up.
(b)
It becomes dimmer.
124
Question Bank (Ch. 8)
2A080104Q022Eng
(a)
What is the relation between the current at each branch and that in the main loop in a parallel
circuit?
___________________________________________________________________________
(b)
What is the relation between the currents at different points in a series circuit?
___________________________________________________________________________
[Ans]
(a)
The current in the main loop is equal to the sum of the currents at all branches.
(b)
They are all the same.
8.8
Fuses
2A080104Q023Eng
(a)
What is the use of a fuse?
___________________________________________________________________________
___________________________________________________________________________
(b)
Explain why circuit breakers are used instead of fuse boxes in modern buildings.
___________________________________________________________________________
___________________________________________________________________________
[Ans]
(a)
The thin wire in the fuse will melt and break the circuit when the electric current is greater than a
certain value. This prevents an excessive electric current from flowing through the circuit.
(b)
Circuit breakers have the same function of fuse boxes and will cut off the current when the current
flowing through the circuit exceeds the rating of the circuit breaker. The circuit can be reconnected
by simply turning the switch to the “ON” position. It is more convenient than fuses, which need to
be replaced after burning out.
8.9
Household Electricity
2A080204Q024Eng
(a)
State TWO advantages of a ring circuit.
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
(b)
How does the circuit breaker protect us?
___________________________________________________________________________
___________________________________________________________________________
[Ans]
(a)
(i) A ring circuit is a type of parallel circuit. So each appliance can be turned on or off
independently. Besides, any faulty appliance would not affect the others to function properly.
(ii) A ring circuit provides two paths for electric current to flow through. It reduces the chance of
overloading because each path only carries half of the current.
(b)
Whenever the circuit is overloaded and the current is too large, it breaks the circuit at the live wire
to stop the current flow. It reduces the chance of electric shock and overheat of appliances.
125
Question Bank (Ch. 8)
2A080104Q025Eng
The photo below shows a mains socket.
A
B
(a)
C
What is the mains voltage in Hong Kong?
___________________________________________________________________________
(b)
Consider the wiring of the sockets.
(i)
Which wire does each of the sockets A, B and C connect to?
_____________________________________________________________________
_____________________________________________________________________
(ii)
Suggest ONE function of the wire connected to socket A.
_____________________________________________________________________
_____________________________________________________________________
[Ans]
(a)
220 V
(b)
(i) A – earth wire; B – neutral wire; C – live wire.
(ii) Earth wire is a safety device and connects the metal case or metal part of the electrical
appliance to the ground.
2A080104Q026Eng
(a)
Suggest TWO possible causes which may lead to a very large electric current flowing through
household circuit.
___________________________________________________________________________
(b)
Why is it dangerous to have a very large electric current to flow through the circuit?
___________________________________________________________________________
___________________________________________________________________________
(c)
What devices can be added to the circuit to protect the circuit from an excessive electric current?
___________________________________________________________________________
[Ans]
(a)
A short circuit and overloading the circuit.
(b)
The wire may get too hot and a fire may occur.
(c)
A fuse or a circuit breaker.
2A080104Q027Eng
Give THREE safety precautions when using electricity at home.
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
126
Question Bank (Ch. 8)
[Ans]
 Use only electrical appliances with three-pin plugs.
 Avoid touching any electrical appliances, mains sockets or switches with wet hands.
 Avoid overloading the circuit.
(Accept other reasonable answers)
8.10 Power of an Electrical Appliance
2A080104Q028Eng
(extension) A light bulb (220 V, 40 W) is connected to a 220 V power source.
(a)
Calculate the size of the electric current flowing through the light bulb.
___________________________________________________________________________
(b)
A hair dryer is connected to the same source. The electric current flowing through it is 5 A. What
is its power?
___________________________________________________________________________
[Ans]
(a)
40 W / 220 V = 0.18 A
(b)
220 V  5 A = 1100 W
2A080104Q029Eng
(extension) A 100 W bulb has been switched on for some time. It consumed 5 units of electricity. How
long has it been switched on? Show your calculations.
_________________________________________________________________________________
_________________________________________________________________________________
[Ans]
Note that 5 units = 5 kW h
Let the time be t hours.
100 t = 5000

t = 50
It has been switched on for 50 hours.
8.11
Cost of Electricity
2A080204Q030Eng
(extension) A compact fluorescent lamp is also called energy-saving blub. It claims it can save up to 80%
of energy. A 20 W CFL is claimed to be as bright as a 100W traditional bulb.
(a)
Which form of energy is the electrical energy in a bulb converted into?
___________________________________________________________________________
(b)
Provided that there is no coiled wire in the CPL. Why can CPL save energy?
___________________________________________________________________________
___________________________________________________________________________
[Ans]
(a)
The electrical energy is converted to light energy and heat energy.
(b)
As there is no coiled wire in the CPL, less electrical energy is converted into heat energy.
Therefore it can save energy.
127
Question Bank (Ch. 8)
Long Questions
2A080105Q001Eng
Study the circuit below and answer the questions.
(a)
What is the function of the switch?
___________________________________________________________________________
(b)
What will happen to the bulb when the switch is on? State the energy change for the whole
process.
___________________________________________________________________________
___________________________________________________________________________
(c)
Suggest TWO materials that could be used to make connectors.
___________________________________________________________________________
(d)
What characteristics of the materials in (c) make them to be connectors?
___________________________________________________________________________
[Ans]
(a)
It turns the bulb on and off.
(b)
The bulb lights up and becomes hot. Chemical energy of the dry cell changes into electrical energy,
and the bulb changes electrical energy into light energy and heat energy.
(c)
Copper and iron could be used to make connectors.
(d)
They are metals and have free electrons that can move freely from one atom to another.
2A080105Q002Eng
Answer the questions according to the circuit below.
(a)
What is the advantage to use circuit symbols to represent different electrical components?
___________________________________________________________________________
___________________________________________________________________________
(b)
List the FOUR components of the circuit.
___________________________________________________________________________
(c)
What are the functions of the components in (b)?
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
128
Question Bank (Ch. 8)
(d)
State THREE conditions to allow a current to flow through the circuit.
___________________________________________________________________________
___________________________________________________________________________
[Ans]
(a)
It is more simple and convenient to draw the electrical components and how they are connected in
a circuit.
(b)
The components are a dry cell, a switch, a bulb and wires/connectors.
(c)
(i) The dry cell provides the voltage. It drives the electrons to flow through the circuit. (ii) The
switch opens and closes the circuit. (iii) The bulb converts electrical energy to light energy and
heat energy. (iv) The wires/connectors provide a path for the current to flow.
(d)
Factors include (i) a dry cell that provides a driving force for electrons, (ii) conducting wires that
provide a path for the electrons to flow and (iii) the whole path must be closed and complete.
2A080105Q003Eng
The diagram below shows a circuit.
instrument A
(a)
What are the TWO major criteria to make the bulb light up in this circuit?
___________________________________________________________________________
(b)
(i)
What is instrument A?
_____________________________________________________________________
(ii)
What does it measure?
_____________________________________________________________________
(iii)
What is the unit of measurement?
_____________________________________________________________________
(c)
Draw a circuit diagram for the above circuit.
129
Question Bank (Ch. 8)
(d)
What will happen to the bulb if
(i)
one more dry cell is added (in proper direction) and the switch is closed?
_____________________________________________________________________
(ii)
one more bulb is added and the switch is closed?
_____________________________________________________________________
[Ans]
(a)
The circuit must be closed and there is a source of electrical energy.
(b)
(i) Ammeter
(ii) The size of an electric current
(iii) Ampere or milliampere
(c)
(d)
(i) The bulb will be brighter.
(ii) The bulb will be dimmer.
2A080105Q004Eng
The diagram below shows a circuit.
instrument X
(a)
(i)
Name instrument X.
_____________________________________________________________________
(ii)
What is the purpose of connecting instrument X in this position?
_____________________________________________________________________
(iii)
Are the bulbs connected in series or in parallel to each other?
_____________________________________________________________________
(b)
If one more dry cell is added (in proper direction), what will happen to
(i)
the reading of instrument X?
_____________________________________________________________________
(ii)
the size of the electric current flowing through the circuit?
_____________________________________________________________________
(iii)
the brightness of the bulbs?
_____________________________________________________________________
130
Question Bank (Ch. 8)
(c)
Draw a circuit diagram for the above circuit.
[Ans]
(a)
(i) Voltmeter
(ii) To measure the voltage of the dry cells or battery
(iii) In series
(b)
(i) The reading will increase.
(ii) The size of the electric current will increase.
(iii) The bulbs will be brighter.
(c)
2A080205Q005Eng
Three different wires, made up of materials X, Y and Z respectively, are connected to the circuit one by
one as shown below.
wire X, Y or Z
The ammeter readings are recorded in the following table.
Material
Ammeter reading (A)
(a)
X
Y
Z
1.3
0.6
0
Which material has the highest resistance? Explain briefly.
___________________________________________________________________________
___________________________________________________________________________
(b)
Which material is Y likely to be, a metal or a non-metal? Explain briefly.
___________________________________________________________________________
___________________________________________________________________________
131
Question Bank (Ch. 8)
(c)
Which material is most suitable to be used as a connecting wire? Explain briefly.
___________________________________________________________________________
___________________________________________________________________________
(d)
Arrange the brightness of the light bulb in an ascending order of the materials of the wire used.
___________________________________________________________________________
(e)
If the ammeter is removed, can we still compare the resistance of X, Y and Z from the circuit?
Explain briefly.
___________________________________________________________________________
___________________________________________________________________________
[Ans]
(a)
Material Z. No electric current can flow through it.
(b)
A metal. It is an electrical conductor.
(c)
Material X. It has the lowest resistance and thus allows a larger electric current to flow through.
(d)
Z<Y<X
(e)
Yes. We can compare the brightness of the bulbs.
2A080105Q006Eng
John wants to make a lamp with an adjustable brightness using the following circuit components. The
design should also allow him to monitor the voltage across the dry cell and the current flows through the
lamp.
V
A
(a)
Draw a circuit diagram in the space above to show the circuit.
(b)
When the resistance of the rheostat increases, what will happen to the readings of the voltmeter
and ammeter?
___________________________________________________________________________
(c)
When the resistance of the rheostat increases, what will happen to the brightness of the bulb?
___________________________________________________________________________
(d)
Suggest another use of a rheostat.
___________________________________________________________________________
132
Question Bank (Ch. 8)
[Ans]
(a)
V
A
(b)
The voltmeter reading does not change while the ammeter reading decreases.
(c)
It becomes dimmer.
(d)
To adjust the volume of a speaker
2A080205Q007Eng
Answer the questions according to the circuit below. All the bulbs are identical.
A
R
A1
A3
A
S
T
A2
A
(a)
The reading of A1 is 3 A.
(i)
What is the sum of the readings of A2 and A3?
_____________________________________________________________________
(ii)
If the reading of A2 is x, what is the reading of A3? Is it 0.5x, x or 2x? (Hint: The current
through a branch is inversely proportional to the resistance of the branch.)
_____________________________________________________________________
(iii)
How many amperes of current flow through bulbs R, S and T respectively?
____________________________________________________________________
(b)
Bulb S is now broken and the reading of A1 becomes 2 A.
(i)
What will happen to the bulbs R and T?
_____________________________________________________________________
(ii)
What are the readings of A2 and A3 now?
_____________________________________________________________________
[Ans]
(a)
(i) 3 A
(ii) 2x
(iii) The currents through bulb R, S and T are 2 A, 1 A and 1 A respectively.
(b)
(i) Bulb T goes out and bulb R remains unaffected.
(ii) The reading of A2 becomes zero and that of A3 remains 2 A.
133
Question Bank (Ch. 8)
2A080205Q008Eng
Peter connected the following circuit. After closing the switch, the bulb goes out immediately.
(a)
Suggest ONE reason why the bulb is gone out immediately after the switch is closed.
___________________________________________________________________________
(b)
Peter used another wire to solve the problem. Suggest THREE relevant characteristics that the new
wire used should have.
___________________________________________________________________________
___________________________________________________________________________
(c)
Suggest another TWO ways to solve the problems.
___________________________________________________________________________
(d)
Draw the circuit symbols of a resistor and a rheostat in the space below.
[Ans]
(a)
The voltage and hence the current is too high.
(b)
The new wire should be longer, thinner and made up of material of high resistance such as
nichrome.
(c)
Use fewer dry cells, connect a resistor in series or connect a rheostat in series.
(Or any reasonable answers)
(d)
rheostat:
resistor:
134
Question Bank (Ch. 8)
2A080105Q009Eng
The diagram below shows a circuit.
Q
rheostat
P
ammeter
(a)
What does the ammeter measure?
___________________________________________________________________________
(b)
The sliding contact of the rheostat is initially at end Q.
(i)
As the sliding contact is moved from end Q to end P, what happens to the brightness of the
bulb?
_____________________________________________________________________
(ii)
What happens to the reading of the ammeter at the same time?
_____________________________________________________________________
(c)
A component is added to the circuit in series to the bulb. As the sliding contact is kept on moving
from end Q to end P, the bulb suddenly goes out.
(i)
What would the component be?
_____________________________________________________________________
(ii)
Draw the circuit symbol for this component in the space below.
[Ans]
(a)
The ammeter is used to measure current.
(b)
(i) The bulb becomes dimmer.
(ii) The reading increases.
(c)
(i) It is a fuse.
(ii)
135
Question Bank (Ch. 8)
2A080105Q010Eng
Below is a circuit diagram.
X
Y
A1
A2
Z
A3
The ammeter readings are recorded in the following table.
(a)
Ammeter
A1
A2
A3
Reading (A)
0.9
0.6
data missing
(i)
Are X and A2 connected in series or in parallel?
_____________________________________________________________________
(ii)
What is the size of the electric current flowing through X?
_____________________________________________________________________
(b)
(i)
Are X and Y connected in series or in parallel?
_____________________________________________________________________
(ii)
Are Y and Z connected in series or in parallel?
_____________________________________________________________________
(c)
(i)
What is the reading of A3?
_____________________________________________________________________
(ii)
What is the size of the electric current flowing through Y?
_____________________________________________________________________
(iii)
What is the size of the electric current flowing through Z?
_____________________________________________________________________
(d)
If Z burns out, will the following bulbs still light up?
(i)
X
_____________________________________________________________________
(ii)
Y
_____________________________________________________________________
[Ans]
(a)
(i) They are in series.
(ii) 0.6 A
(b)
(i) They are in parallel.
(ii) They are in series.
(c)
(i) 0.9 A – 0.6 A = 0.3 A
(ii) 0.3 A
(iii) 0.3 A
(d)
(i) Yes, it still lights up.
(ii) No, it will not light up.
136
Question Bank (Ch. 8)
2A080105Q011Eng
(a)
What do the following symbols represent?
(i) ________________
(b)
(c)
(ii) ________________
(iii) ________________
What are their uses?
(i)
________________________________________________________________
(ii)
________________________________________________________________
(iii)
________________________________________________________________
There are four colour bands printed on component (a)(ii). What do they mean?
___________________________________________________________________________
(d)
There is a marking ‘5 A’ printed on the surface of component (a)(iii). What does it mean?
___________________________________________________________________________
[Ans]
(a)
(i) Rheostat
(ii) Resistor
(iii) Fuse
(b)
(i) A rheostat is used to vary the size of an electric current flowing through a circuit.
(ii) A resistor is used to adjust the size of an electric current flowing through a circuit.
(iii) A fuse is used to protect the electrical appliance from being damaged by excessive currents in
electric circuits.
(c)
The colour bands show the resistance of the resistor.
(d)
It means the fuse will burn out if the current flowing through it is larger than 5 A.
2A080205Q012Eng
Study the following circuits and answer the questions.
A.
B.
C.
D.
E.
137
Question Bank (Ch. 8)
(a)
Which circuit(s) has/have no branch?
___________________________________________________________________________
(b)
Which circuit(s) has/have more than two branches?
___________________________________________________________________________
(c)
In which circuit(s) has/have all bulbs same brightness?
___________________________________________________________________________
(d)
In which circuit would all bulbs go out by removing one bulb?
___________________________________________________________________________
(e)
In which circuit do all bulbs not light up? Why?
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
[Ans]
(a)
E
(b)
A, B, C, D
(c)
B, C, E
(d)
E
(e)
C. It is because there is a low-resistance shortcut for the current to bypass all the bulbs.
2A080105Q013Eng
The diagram below shows a circuit.
power supply
fuse
(a)
What is the function of the fuse in the circuit?
___________________________________________________________________________
___________________________________________________________________________
(b)
If the working current of the bulb is 0.75 A and there are fuses with fuse ratings of 0.5 A, 1 A and
2 A, which fuse would you use?
___________________________________________________________________________
(c)
Give TWO characteristics of the wire in the fuse.
___________________________________________________________________________
___________________________________________________________________________
(d)
Name the effect that makes the bulb light up. Also write down the energy changes in this effect.
___________________________________________________________________________
___________________________________________________________________________
138
Question Bank (Ch. 8)
(e)
What will happen to the brightness of the bulb if
(i)
a fuse with the fuse rating of 0.5 A is used?
_____________________________________________________________________
(ii)
the voltage from the power supply is increased?
_____________________________________________________________________
(iii)
one more bulb is added in series?
_____________________________________________________________________
[Ans]
(a)
To prevent an excessive electric current from flowing through the circuit
(b)
1A
(c)
The wire is thin and made from a metal with a low melting point.
(d)
The heating effect of an electric current
Electrical energy is changed into heat energy. And some of the heat energy is changed into light
energy.
(e)
(i) The bulb will go out.
(ii) The bulb will be brighter.
(iii) The bulb will be dimmer.
2A080105Q014Eng
(a)
What is the voltage of the mains electricity in our homes?
___________________________________________________________________________
(b)
(i)
What is the current passing through a 100 W bulb?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
(ii)
How much electrical energy will be consumed if the 100 W bulb is turned on for 10 hours?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
(c)
(i)
What is the current passing through a 20 W compact fluorescent lamp?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
(ii)
How much electrical energy will be consumed if the 20 W CFL is turned on for 10 hours?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
(d)
Comparing the answers in (b)(ii) with (c)(ii), how many percent of electrical energy is saved?
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
139
Question Bank (Ch. 8)
[Ans]
(a)
220 V
(b)
(i) P = 100 W; V = 220 V
I = P/V = 100 W/220 V = 0.45 A
(ii) 100 W=0.1 kW
For 10 hours, the energy consumed = 0.1 kW  10 h = 1 kW h
(c)
(i) P = 20 W; V = 220 V
I = P/V = 20 W/220 V = 0.09 A
(ii) 20 W = 0.02 kW
For 10 hours, the energy consumed = 0.02 kW  10 h = 0.2 kW h
(d)
(1 – 0.2)/1  100% = 80%
Therefore, 80% of energy is saved.
2A080105Q015Eng
The cost of electricity in Hong Kong is calculated as follows:
The first 400 units: $0.86 for each unit
The coming 600 units: $0.93 for each unit
After 1000 units: $0.996 for each unit
(a)
There is an electricity bill which states that a family spent 1380 units of electricity in the past two
months. Calculate the cost of electricity.
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
(b)
The cost of electricity is very expensive. Suggest TWO ways to reduce the consumption of
electricity.
___________________________________________________________________________
___________________________________________________________________________
(c)
How can compact fluorescent lamps save energy?
___________________________________________________________________________
(d)
Why are overloading and short circuits dangerous?
___________________________________________________________________________
___________________________________________________________________________
[Ans]
(a)
1380= 400 + 600 + 380
Cost of electricity:
(400 × $0.86) + (600 × $0.93) + (380 × $0.996)
= $344 + $558 + $378.84
= $1280.84
(b)
Switch off the appliances when they are not in use.
Use compact fluorescent lamps (power saving bulbs) instead of ordinary bulbs.
(c)
Less heat is produced from a CFL lamp, therefore it can save energy.
140
Question Bank (Ch. 8)
(d)
If too many electrical appliances connected to a mains socket are turned on at the same time, the
circuit will be overloaded and a lot of heat will be generated. The large amount of heat generated
may cause an electrical fire.
Since the resistance of a short circuit is very low, the electric current in the circuit becomes very
large. This may lead to a great heating effect and cause a fire.
2A080105Q016Eng
The diagram below shows a three-pin plug.
wire Y
wire Z
fuse
wire X
(a)
(i)
Give the name for wire Y.
_____________________________________________________________________
(ii)
Which part of the electrical appliance is it connected to?
_____________________________________________________________________
(iii)
How does it protect us from an electric shock?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
(b)
(i)
Give the name for wire X.
_____________________________________________________________________
(ii)
What is its colour?
_____________________________________________________________________
(c)
(i)
Give the name for wire Z.
_____________________________________________________________________
(ii)
What happens if the connection of wires Y and Z is interchanged wrongly?
_____________________________________________________________________
_____________________________________________________________________
(d)
What will happen to the fuse and the electrical appliance if there is an excessive electric current
flowing through wire Z?
___________________________________________________________________________
___________________________________________________________________________
(e)
In some countries, only two-pin plugs are used. Which wire is missing in this kind of plugs?
___________________________________________________________________________
141
Question Bank (Ch. 8)
[Ans]
(a)
(i) Earth wire
(ii) Metal case
(iii) If an electric current leaks to the metal case, the electric current will flow through the earth
wire to the ground. This prevents an electric shock if we touch the metal case accidentally.
(b)
(i) Neutral wire
(ii) Blue
(c)
(i) Live wire
(ii) The electrical appliance will not work.
(d)
The fuse will burn out. The electrical appliance will not work
(e)
Earth wire
2A080105Q017Eng
This question is about short circuit and electricity safety.
(a)
Modify the following diagram to show how a short circuit is formed.
appliance
X
(b)
(i)
A short circuit is a danger of using electricity. Suggest another danger of using electricity.
_____________________________________________________________________
(ii)
Why is the case you mentioned in (i) dangerous?
_____________________________________________________________________
_____________________________________________________________________
(c)
Give THREE safety precautions when using electricity.
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
[Ans]
(a)
appliance
X
(b)
(i) Overloading of the circuit
(ii) When the circuit is overloaded, a lot of heat will be generated. The electric cables become so
hot that an electrical fire may occur.
142
Question Bank (Ch. 8)
(c)
 Arrange for a registered electrical technician to replace damaged wires, plugs or mains sockets
immediately.
 Do not use any flammable substances near an operating electrical appliance.
 Avoid using electrical appliances like heaters in bathrooms.
(Or any other three reasonable answers)
2A080105Q018Eng
(extension) The following table shows the electrical appliances that Albert used in one evening. Assume
the mains voltage is 220 V.
Electrical appliance
(kW)
Duration of use
Amount of electrical
energy consumed (kW h)
Electric fan
0.08
4 hours
(i) _________________
Fluorescent tube
0.03
4 hours 15 minutes
(ii) _________________
Television set
0.14
1 hour 30 minutes
(iii) _________________
VCD player
0.02
1 hour
(iv) _________________
0.005
2 hours 45 minutes
(v) _________________
0.14
3 minutes
(vi) _________________
Mobile phone
charger
Fax machine
(a)
Power
Calculate the amount of electrical energy consumed for each electrical appliance. Show your steps
in the space below and complete the above table.
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
(b)
If each unit of electricity costs $0.9, what will be the total cost of electricity?
___________________________________________________________________________
___________________________________________________________________________
(c)
Which electrical appliance has the smallest working current? What is its working current?
(Express the answer in mA.)
___________________________________________________________________________
___________________________________________________________________________
(d)
Suggest TWO ways of reducing the consumption of electricity.
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
143
Question Bank (Ch. 8)
[Ans]
(a)
(i) Electric fan: 0.08 kW  4 h = 0.32 kW h
(ii) Fluorescent tube: 0.03 kW  4.25 h = 0.1275 kW h
(iii) Television set: 0.14 kW  1.5 h = 0.21 kW h
(iv) VCD player: 0.02 kW  1 h = 0.02 kW h
(v) Mobile phone charger: 0.005 kW  2.75 h = 0.0138 kW h
(vi) Fax machine: 0.14 kW  (3/60) h = 0.007 kW h
(b)
Total cost of electricity
= (0.32 + 0.1275 + 0.21 + 0.02 + 0.0138 +0.007)  $0.9
= 0.6983  $0.9
= $0.6284
(c)
Mobile phone charger.
Working current
= power / voltage
= 0.005 kW / 220 V
= 5 W / 220 V
= 0.0227 A
= 22.7 mA
(d)
 Turn off the electrical appliances when not in use.
 Iron clothing in bulk. Handle clothing that requires high heat first. Then turn off the iron and
make use of the residual heat to iron other clothing that requires careful treatment.
(Or other two reasonable answers)
2A080105Q019Eng
(extension) The photos below show an electric iron and a washing machine in Mary’s home.
Electric iron
(a)
Washing machine
Name the working principle for each of the above electrical appliances. For each principle, suggest
ONE electrical appliance other than those shown above which works on the same principle.
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
(b)
Which part of the iron are the live wire and the neutral wire connected to?
___________________________________________________________________________
___________________________________________________________________________
144
Question Bank (Ch. 8)
(c)
What is the name for the connection of the earth wire from the metal case of the iron to the
ground?
___________________________________________________________________________
(d)
Consider Mary’s washing machine.
(i)
Calculate the electric current flowing through the washing machine if the power is 520 W
and it is used in Hong Kong.
_____________________________________________________________________
(ii)
Calculate the amount of electrical energy consumed in December if the washing machine is
operated for 2.5 hours each time and it is used every day.
_____________________________________________________________________
(iii)
Calculate the cost of electricity for using the washing machine in December if the unit cost
of electricity is $0.9.
_____________________________________________________________________
[Ans]
(a)
Electric iron: heating effect of an electric current
Other examples: toasters / ovens / electric heaters (or other reasonable answers)
Washing machine: magnetic effect of an electric current
Other examples: electric door bells / loudspeakers / blenders (or other reasonable answers)
(b)
The heating element
(c)
Earthing
(d)
(i) I = P / V = 520 W / 220 V = 2.36 A
(ii) E = P  t = 0.52 kW  2.5  31 = 40.3 kW h
(iii) Cost of electricity = 40.3 kW h  $0.9 = $36.27
2A080105Q020Eng
Study the following circuit and answer the questions.
(a)
After closing the switch, will the coil get hotter, cooler or remain unchanged?
___________________________________________________________________________
(b)
If iron nails are put near the coil after closing the switch, what will happen?
___________________________________________________________________________
(c)
Name the effect of an electric current shown in (b).
___________________________________________________________________________
(d)
Give TWO examples of electrical appliances that work on the effect mentioned in (c).
___________________________________________________________________________
145
Question Bank (Ch. 8)
[Ans]
(a)
It will get hotter.
(b)
Iron nails will be attracted by the coil if they are put near the coil.
(c)
Magnetic effect of an electric current
(d)
Speakers and washing machines (Or any other reasonable answers)
Miscellaneous Questions
2A080106Q001Eng
Common fuse ratings include 1 A, 3 A, 5 A, 13 A, 15 A and 30 A. Choose a fuse with a correct fuse rating
for the following electrical appliances.
Electrical appliances
Working current (A)
Fuse rating (A)
Light bulb
0.3
(a)
Electric fan
1.1
(b)
Hair dryer
2.5
(c)
Electric iron
4
(d)
Air conditioner
10
(e)
Electric heater
14
(f)
[Ans]
(a) 1
(b) 3
(c) 3
(d) 5
(e) 13
(f) 15
2A080106Q002Eng
Match the objects on the left and the descriptions on the right in the following table. Write your answers
in the blanks below.
Object
Description
(a)
A circuit breaker
(i)
(b)
An electric iron
(c)
An ammeter
(d)
A switch
(e)
A resistor
(iii)
is used to measure the size of an electric current.
(f)
An electric door
(iv)
stops or allows the flow of an electric current.
bell
(v)
is a safety device to protect electrical appliances in our homes.
(vi)
is a component with a fixed resistance used to reduce the size
is an electrical appliance which makes use of the magnetic
effect of an electric current.
(ii)
is an electrical appliance which makes use of the heating
effect of an electric current.
of an electric current flowing through a circuit.
(a) ______
(b) ______
(c) ______
(d) ______
(e) ______
(f) ______
[Ans]
(a) v
(b) ii
(c) iii
(d) iv (e) vi
(f) i
146
Question Bank (Ch. 8)
2A080106Q003Eng
Match the objects on the left and the descriptions on the right in the following table. Write your answers
in the blanks below.
Object
Description
(a)
A closed circuit
(i)
(b)
A rheostat
(c)
A fuse
(d)
An electromagnet
(e)
A kilowatt-hour meter
contains a piece of metal wire that melts when
a current larger than its rating flows through it.
(ii)
behaves like a magnet when an electric current
flows through it.
(iii)
is a complete route which an electric current
can flow through.
(a) ______
(iv)
is used to measure the power consumption.
(v)
has an adjustable resistance.
(b) ______
(c) ______
(d) ______
(e) ______
[Ans]
(a) iii
(b) v
(c) i (d) ii (e) iv
2A080106Q004Eng
Label the following figure:
(a)
(b)
(c)
[Ans]
(a) earth socket
(b) neutral socket
(c) live socket
2A080106Q005Eng
Label the following figure:
(d)
(f)
(e)
[Ans]
(d) live pin
(e) neutral pin
(f) earth pin
147
Question Bank (Ch. 8)
2A080106Q006Eng
Label the following figure:
(g)
(i)
(h)
(j)
[Ans]
(g) earth wire
(h) neutral wire
(i) live wire
(j) fuse
2A080206Q007Eng
There following statements are INCORRECT. Underline the wrong word (s) on the left column and write
the correct words on the right column. There might be more than one mistake in each sentence.
Statement
Correction
(a)
Ampere is the flow of electrons
(b)
Electricity is a form of force. It can be changed into other
forms of force.
(c)
A current is a path for electricity to flow through
(d)
All conductors are metals.
(e)
Open a circuit can light up a bulb
[Ans]
(a)
Ampere  Current
(b)
force  energy (2)
(c)
current  circuit
(d)
All  Most
(e)
Open  Close
2A080206Q008Eng
The following statements are INCORRECT. Circle the wrong word(s) on the left column and write the
correct ones on the right column. There might be more than one mistake in each sentence.
Statement
Correction
(a)
Closing a switch makes the circuit incomplete.
(b)
A substance that allows current to flow through is called
an electrical insulator.
(c)
An atom consists of negatively charged electrons and an
uncharged nucleus.
(d)
Electric current refers to the random flow of free electrons.
(e)
The symbol for the unit of current is I.
148
Question Bank (Ch. 8)
[Ans]
(a)
Closing  Opening
(b)
insulator  conductor
(c)
an uncharged nucleus  a positively charged nucleus
(d)
random  unidirectional
(e)
IA
2A080206Q009Eng
The following statements are INCORRECT. Circle the wrong word(s) on the left column and write the
correct ones on the right column. There might be more than one mistake in each sentence.
Statement
(a)
Correction
Both voltage and the resistance will increase if we connect
more dry cells to the circuit in proper direction.
(b)
The red terminal of a voltmeter should connect to the negative
pole of a dry cell when measuring the voltage of a dry cell.
(c)
The resistance of a wire increases as the thickness of the wire
increases or the length of the wire increases.
(d)
A resistor is a device to measure the size of resistance of a
circuit.
[Ans]
(a)
resistance  current
(b)
negative pole  positive pole
(c)
increasing  decreasing
(d)
measure  control
2A080206Q010Eng
(extension) The following statements are INCORRECT. Circle the wrong word(s) on the left column and
write the correct ones on the right column. There might be more than one mistake in each sentence.
Statement
(a)
Correction
The circuits in our homes are called chained circuit, in which
mains sockets are connected in parallel.
(b)
The colour of earth wire is brown.
(c)
The power of a bulb represents the amount of electrical energy
consumed by the bulb.
(d)
The energy consumed in our homes is measured by wattmeter.
(e)
The two major working principles of common electrical
appliances are the shocking effect and shaking effect of an
electric current.
149
Question Bank (Ch. 8)
[Ans]
(a)
The circuits in our homes are called chained (ring) circuit, in which mains sockets are connected in
parallel.
(b)
The colour of earth wire is brown (yellow and green).
(c)
The power of a bulb represents the amount of electrical energy consumed (electrical energy
consumed per second) by the bulb.
(d)
The energy consumed in our homes is measured by wattmeter (kilowatt-hour meter).
(e)
The two major working principles of common electrical appliances are the shocking (heating)
effect and shaking (magnetic) effect of an electric current.
2A080106Q011Eng
What is wrong with the following sentences? Underline the words and rewrite the correct sentences.
(a)
A fuse is rated in ohms.
___________________________________________________________________________
(b)
A fuse wire has a high melting point.
___________________________________________________________________________
(c)
A fuse makes use of the magnetic effect of an electric current.
___________________________________________________________________________
(d)
The fuse rating of a fuse should be lower than the working current of the electrical appliance.
___________________________________________________________________________
(e)
The fuse is connected to the neutral wire of a three-pin plug.
___________________________________________________________________________
[Ans]
(a)
A fuse is rated in ohms (amperes).
(b)
A fuse wire has a high (low) melting point.
(c)
A fuse makes use of the magnetic (heating) effect of an electric current.
(d)
The fuse rating of a fuse should be lower (higher) than the working current of the electrical
appliance.
(e)
The fuse is connected to the neutral (live) wire of a three-pin plug.
2A080206Q012Eng
Match the symbols and the devices. Write down the usage of the devices.
A.
(a) fuse: ______
________________________________________
________________________________________
B.
(b) rheostat: ______
________________________________________
V
________________________________________
150
Question Bank (Ch. 8)
C.
(c) switch: ______
________________________________________
________________________________________
D.
(d) ammeter: ______
________________________________________
A
________________________________________
E.
(e) voltmeter: ______
________________________________________
________________________________________
[Ans]
(a)
E: A device burns out under excessive current to protect the appliance from being damaged.
(b)
A: A device that control the resistance of a circuit.
(c)
C: To open or close a circuit.
(d)
D: To measure the size of electric current flow.
(e)
B: To measure the size of voltage.
2A080206Q013Eng
Mary is going to make a Christmas lighting. She is thinking how to connect the bulbs, i.e. in series or in
parallel. Help her by complete the following table with suitable words
Series circuit
Effect on current
Parallel circuit
Current
Current in main loop
(a)________________ when
(b)____________ when
number of bulbs increases
number of branch increases
The circuit
Current
(c)_______________ and no
(d)_________________ to
current flows
other branches.
Chances of overloading
(e)
(f)
Advantage
(g)
(h)
Disadvantage
(i)
(j)
Effect of a broken bulb
[Ans]
(a) decreases
(b) increases
(g) Simple and easy to install
(c) breaks
(d) flows
(e) No
(f) Yes
(h) Able to control each appliance independently
(i) Unable to control each appliance independently
(j) Easy to overload the main loop
151
Question Bank (Ch. 8)
2A080106Q014Eng
Complete the following table with suitable words.
(i) Voltage
(a)
Measured by
(b)
Unit
(c)
Unit symbol
(d)
Affected by if the circuit is broken?
(ii) Current
[Ans]
(a)
(i) voltmeter
(b)
(i) volt
(c)
(i) V
(d)
(i) No
(ii) ammeter
(ii) ampere
(ii) A
(ii) Yes
2A080206Q015Eng
With the electrical components provided, design a circuit by drawing a circuit diagram to study the
relation between voltage, resistance and current in a parallel circuit.
Component
Number
Voltmeter
1
Ammeter
3
Rheostat
2
Dry cell
1
Wires
many
152
Question Bank (Ch. 8)
[Ans]
V
A
A
A
2A080106Q016Eng
Draw the circuit diagram for the following circuit.
[Ans]
153
Question Bank (Ch. 8)
2A080106Q017Eng
Draw the circuit diagram for the following circuit.
[Ans]
2A080206Q018Eng
Draw the circuit diagram for the following circuit.
154
Question Bank (Ch. 8)
[Ans]
2A080206Q019Eng
Write a short paragraph with the words provided below to explain the difference between a conductor and
an insulator.
conductor, insulator, free electrons, voltage, current
(a)
In a conductor, ______________________________________________________________
(b)
When a voltage is applied to a conductor, _________________________________________
___________________________________________________________________________
(c)
In an insulator, ______________________________________________________________
(d)
When a voltage is applied to an insulator, _________________________________________
___________________________________________________________________________
[Ans]
(a)
In a conductor, there are a lot of free electrons.
(b)
When a voltage is applied to it, free electrons flows in one direction and form a current.
(c)
In an insulator, there is almost no free electron.
(d)
When a voltage is applied to it, no current can be formed.
2A080206Q020Eng
Write a short paragraph about home electricity safety with the words provided below.
accidents, fire, overloading, short circuit, fuse, circuit breaker
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
[Ans]
Overloading and short circuit are two common accidents in using electrical appliances in home. Serious
cases result in a fire. To prevent this, a fuse should be installed to the live wire in every plug and circuit
breakers should be installed in the mains circuit.
155