Intermediate 1
Physics
Practical Electricity
Questions
and
Answers
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Intermediate 1
Physics
Practical Electricity
Questions 1 to 10
Questions 11 to 20
Questions 21 to 30
Questions 31 to 40
Questions 41 to 46
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1.
Draw the circuit symbols for, a voltmeter; an electric
motor; a switch and a fuse.
voltmeter =
V
electric motor =
M
switch =
fuse =
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2. Beside each of the following symbols write the name
of the component and state what it does.
battery
supplies energy
lamp
changes electrical energy
to light energy
fixed resistor
opposes current and
produces heat
variable resistor controls current
A
ammeter
measures current
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3. Draw circuit diagrams showing:
(a) a battery, a lamp and two resistors all in series
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3. Draw circuit diagrams showing:
(b) a battery, two lamps, a switch and an ammeter all
in series
A
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3. Draw circuit diagrams showing:
(c) a battery and three lamps in parallel
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3. Draw circuit diagrams showing:
(d) a battery and switch in series, connected to three
resistors in parallel with each other.
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4. Redraw the circuit below showing how to measure the
current through the lamp.
A
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5. Redraw the circuit of question 4 showing how to
measure the voltage across the lamp.
V
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6. Write the reading of the ammeters beside each
ammeter symbol.
0.9 A
A
A
0.9 A
A
0.9 A
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7. Redraw the circuit of question 6 without the
ammeters and show how you would connect a
voltmeter to measure the supply voltage
V
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8. In the circuit below, the lamps are identical and the
current through each lamp is 0.6 A.
Mark beside each component the value of the current
through it.
0.6 A
0.6 A
1.2 A
1.2 A
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9. In the circuit below the ammeter reads 0.6 amperes.
What is the value of the current through the lamp?.
0.6 A
A
0.6 A
because the
current is the
same everywhere
in a series circuit
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10. In the circuit below, ammeter A1 reads 0.2 amperes
and ammeter A2 reads 0.5 amperes.
Beside each component, write its name and the value
of the current through it.
battery
0.5 A
0.5 A
lamp
0.5 A
A2
resistor
0.2 A
0.2 A
A1
heater
0.3 A
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11. Redraw the circuit of question 10 and show how the
voltage across the lamp can be measured.
A2
V
A1
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12. In this circuit, the lamps are different.
The voltmeter reads 3 volts.
What is the voltage across the other lamp L2?
8.0 V
L2
reading = Vsupply – Vlamp1
V
3.0 V
= 8.0 V – 3.0 V
= 5.0 V
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13. In the circuit below, the voltmeter reads 4 volts.
What is the voltage across the resistor R?
the voltage is the same across
components which are in
R
parallel.
the voltage across R = 4 volts
V
4 volts
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14. In the circuit below, the voltages are as shown.
What is the voltage of the supply?
Vsupply = 4 V + 6 V = 10 V
V
V
4V
6V
voltages in a series circuit add up to the
supply voltage.
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15. In the circuit below, the voltages are shown. What is
the voltage across the second resistor?
24 V
V
8V
V
Vresistor = 24 V - 8 V = 16 V
voltages in a series circuit add up to the
supply voltage.
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16. This diagram shows a 6 V bulb working correctly off a
24 V supply. What must be the voltage across the
resistor?
24 V
Vresistor = 24 V - 6 V
6V
= 18 V
voltages in a series circuit add up to the
supply voltage.
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17. The diagram shows the circuit of the courtesy light in
a two-door car.
A car courtesy light
operates when either door
of the car is opened.
S1
courtesy
light
S2
(a) What happens to a switch when a door is opened?
The switch closes (and completes the circuit).
(b) Explain why the switches are in parallel rather than in series.
This means that when either door is opened, the circuit
is completed and so the courtesy lamp lights.
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18. A resistor has a voltage across it of 12 volts and a
current through it of 2 amperes.
Calculate the resistance of the resistor.
resistance =
voltage
current
12
=
2
= 6W
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19. A voltage of 6 volts is across a resistor where the
current is 0.5 amperes.
What is the value of the resistor?
resistance =
voltage
current
6
=
0.5
= 12 W
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20. Calculate the resistance of a component when a
voltage of 24 V causes a current of 0.1 amperes.
resistance =
voltage
current
24
=
0.1
= 240 W
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21. If a current of 2 amperes exists through a lamp when
it has 12 volts across it, what is the resistance of the
lamp?
resistance =
voltage
current
12
=
2
= 6W
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22. A torch bulb is marked "6 V, 0.25 A".
Calculate the resistance of the bulb.
resistance =
voltage
current
6
=
0.25
= 24 W
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23. A resistor is placed in a circuit. The voltage across it
and current through it are measured as 12 volts and
0.02 amperes.
The resistor is now removed from the circuit and an
ohmmeter connected across it.
What is the reading on the ohmmeter?
resistance =
voltage
current
12
=
0.02
= 600 W
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24. (a) Find the values of the resistors in the circuit
below.
2V
3V
5V
V
V
V
R1
R2
R3
0.25 A
V
2
R1 =
=
= 8W
I
0.25
R2
R3
V
3
=
=
= 12 W
I
0.25
V
5
=
=
= 20 W
I
0.25
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24. (b) Calculate the value of the supply voltage.
2V
3V
5V
V
V
V
R1
R2
R3
0.25 A
voltages in a series circuit add up to the supply voltage.
so, Vsupply = 2 V + 3 V + 5 V
= 10 V
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25. Explain why it is dangerous to operate mains switches
with wet hands.
The human body conducts better when wet.
It is therefore more likely that you could be
electrocuted,
and mains voltage can cause a current large
enough to kill you.
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26. Describe an experiment to show the change in
conductivity of the human body when it is dry or wet.
Hold the terminals of an ohmmeter in separate
hands.
Take a reading of the resistance of your body.
Wet your hands and repeat the experiment.
Your resistance will have reduced showing that
your body is a better conductor when it is wet.
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27. Draw a sketch of a domestic three-pin plug.
Label the wires; live, neutral and earth and state the
colours of their insulation.
Label the fuse and describe how it works.
e_ a_ _r _t _h pin
Earth wire
l l_ o_ w_ )
(Green/ y
_ e
_ _
Live wire
r _o w
n)
(b
_ _
_ _
s _e
Fu
_ _
Neutral wire
l u_ e_ )
(b
_ _
cable grip
n_ e
u _t _r _a _l
_ _
pin
l i_ v_ e_
_
pin
The fuse is a wire which melts and breaks the
circuit if too high a current flows.
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28. Draw the symbol for a double insulated appliance.
Describe what is meant by "double insulated".
A double insulated appliance has an insulated
casing which cannot become ‘live’.
You cannot be electrocuted touching its casing and
so it does not need an earth wire.
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29. What are the advantages of using a circuit breaker
instead of a fuse?
•A circuit breaker is faster in switching off a
circuit than a fuse is
•A circuit breaker is easier to reset than
rewiring a fuse
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30. Which fuse value is required for an appliance with a
power of 1150 watts?
current =
power
voltage
=
1150
230
= 5A
Therefore a 13 ampere fuse is required.
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31. A mains appliance has a power rating of 820 watts.
How much current does it require?
current =
power
voltage
=
820
230
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= 3.6 A
37
32. How much current will a 2 kilowatt mains heater
require?
current =
power
voltage
=
2000
230
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= 8.7 A
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33. Mains plugs can have a choice of two values; 3 A and
13 A.
Which fuse should be inserted in a plug attached to a
750 watt appliance?
current =
power
voltage
=
750
230
= 3.3 A
A 3 A fuse would be too low as it would
be melted by a current of 3.3 A.
Therefore a 13 ampere fuse is required.
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34. A lighting circuit in a house serves 6 rooms. If each
room can have a maximum of 150 watts per ceiling
lamp, what value of fuse should be used to protect
the circuit?
current =
power
voltage
=
6 x 150
230
=
900
230
= 3.9 A
Therefore a 5 ampere fuse is suitable
for this lighting circuit.
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35. Complete the following sentences to make 4 important
safety rules for mains electricity.
(a) Never use worn or damaged
could get a shock from an exposed
flexes
live
: you
wire.
extensions
(b) Avoid the use of
if possible: too
many appliances connected to an adaptor could
produce overheating at the socket.
(c) Always use the correct flex: a flex which is
thin
too
could overheat.
fuse
(d) Always use the correct plug
: if
high and a fault develops,
the fuse rating is too
the flex could overheat.
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36. Describe how to use a multimeter to detect an open
circuit. Make sure you include how to set the
multimeter to the correct setting and what you would
expect to see for this fault.
Set the multimeter to be an ohmmeter
(i.e. a resistance meter).
Connect the ohmmeter to the circuit.
The circuit is broken (i.e. an open circuit)
if the reading is “off scale” (i.e. 1 .
).
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37. The circuit shown below contains a battery, lamp, 1 A
fuse and a variable resistor.
(a) Is this a series or a parallel circuit?
series ; because there is only one path for current.
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37. (b)The variable resistor is set so that a current of
2 A flows.
(i)
What happens to the fuse when
there is a current of 2 A?
It melts/breaks/blows.
(This is because it allows a maximum
current of 1 A.)
(ii)
What happens to the lamp when
there is a current of 2 A in the
fuse? Explain your answer.
The lamp stops lighting/goes off.
This is because, when the fuse melts, the
circuit is broken and so the current stops.
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38. A group of pupils investigate the time various
appliances are switched on for during a day.
The appliances are all rated at 100 W.
Their results are presented in the bar chart below.
8
7
6
5
4
3
2
1
0
Lamp
Mixer
Stereo
Electric Knif e
Alarm
(a) Which of the appliances is switched on for the
longest time? The lamp,
because its bar is the highest.
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38. (b) All of the appliances have a power rating of 100 W.
Explain which of the appliances is most costly to
use in one day.
The lamp,
because, being on for longer, it uses more
electrical energy than the other appliances.
You should note that a higher powered
appliance (like a heater) can cost more to use
even if it is on for a shorter time.
This is because it is using electrical energy at a
faster rate.
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39. The following table gives details about various
household appliances.
Name of
Table Lamp
Kettle
Appliance
Washing
Curling
Machine
Tongs
Power
60W
2kW
1.8kW
300W
Voltage
230V
230V
230V
230V
Current
0.26 A
8.7 A
7.8 A
1.3 A
(a) Complete the table shown above.
(b) List all the appliances in the table which should
have a 3 A fuse fitted in their plug.
The table lamp and the curling tongs.
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40. Shown below is a parallel circuit containing a battery,
resistor, lamp and two ammeters.
The following readings are
taken from the ammeters:
Reading on A1 = 0.05 A
Reading on A2 = 0.42 A
A1
A2
(a) State the current through the lamp. 0.42 A
(b) Which component, the resistor or the lamp, has
the larger resistance? Explain your answer. the resistor
It has a smaller current through it.
The current has split with most of it taking the
easier path through the lamp.
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41. The adverts shown below give information on two music
systems.
PONY
VMJ
Mains
4 Watts
ORDER 684-209
£99.99
Mains
5 Watts
ORDER 1214-7821
£129.99
(a) Explain which music system is the more expensive to
operate. The VMJ one as it has a higher power rating.
(b) Both of these systems need to be connected to the
mains supply. State the voltage across these systems when
connected to the mains.
230 V
(c) Calculate the current in the ‘Pony’ music system.
power
current =
voltage
=
4
230
= 0.017 A
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42. A continuity tester is shown.
(a) A piece of bare copper wire is connected to both
metal probes. Will the lamp light?
Yes,
because the thick copper has a very low
resistance and completes the circuit.
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42. (b) The circuit below contains 2 copper wires covered
in plastic and a heater.
Copper w i re covered i n plasti c i nsulati on
A test engineer suspects that there is an open circuit
fault.
Describe how the continuity tester can be used to
test if there is an open circuit.
Set the multimeter to be an ohmmeter (i.e. a
resistance meter).
Connect the ohmmeter to the two terminals.
The circuit is an open circuit if the reading is 1 .
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42. (c) The continuity tester is connected to the L and N
pins of the plug of the appliance shown below.
The lamp does not light.
Complete the following sentences:
Since the lamp does not light this must be an open
circuit.
This could be because there is a broken
wire
off
or the on/off switch is in the
position.
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43. A car accessory shop sells a hand held search lamp which
works with a car battery.
A motorist buys the hand held search lamp and decides to
check its resistance.
(a) Complete the diagram below to show how this could
be done using an ammeter and voltmeter.
V
XPOWER
battery
A
(b) How would the motorist use the readings to find
the resistance of the search lamp? (SEB 1990)
resistance =
voltage reading
current reading
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44. The diagram shows the wire of a food processor
correctly connected to a three pin plug.
(a) Complete the table below naming the colour of the
insulation on the wires connected to pins L and N.
Pin
Colour of insulation
L
brown
N
blue
(b) One pin of the plug has not been used because the
food processor is double insulated.
(i) What name is given to the pin which has not
been used? earth
(ii) Draw the double insulation symbol. (SEB 1990)
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45. The circuit shown is used to investigate the effect of a
variable resistor in a circuit.
V
A
The variable resistor setting is gradually changed.
The readings taken from the meters are shown in the table
below.
Set 1 was the first set of readings, set 2 the second, etc.
The readings were taken in the order shown.
Voltage
(volts)
Current
(amperes)
Set 1
Set 2
Set 3
Set 4
6
6
6
6
0.1
0.2
0.3
0.4
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45. (a) Was the resistance of the variable resistor
increased or decreased during the experiment?
Explain your answer.
Its resistance was decreased;
the current was increasing showing that it was
becoming easier for current to flow.
(b) Calculate the resistance at the lowest setting of
the variable resistor in this experiment.
voltage
resistance =
current
6
=
0.4
= 15 W
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46. Various appliances and the value of the fuse they need are
listed below.
Computer: 3 A, Toaster: 13 A, Hair dryer: 13 A, CD player:
3 A, Coffee percolator: 3 A, Vacuum cleaner: 13 A.
Construct a table, with suitable headings, which lists the
appliances in two groups. One group should contain those
appliances requiring a 3 A fuse. The second group should
contain those appliances requiring a 13 A fuse.
Appliances using 3 A fuse
Appliances using 13 A fuse
Computer
Toaster
CD player
Hair dryer
Coffee percolator
Vacuum cleaner
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Intermediate 1
Physics
Practical Electricity
End of
Questions and
Answers
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