Year 10 Syllabus Revision– Suggested Answers 6-9
ELECTRICITY
6. Design, construct and draw circuits containing a number of components.
When drawing electrical circuits, standard symbols are used to represent the components
of the circuit. These symbols are:
connecting wire resistor -
fuse OR
(two cells in series – battery)
electric cell or power supply -
closed switch -
light globe ammeter
voltmeter 
open
switch -
-
Draw the following circuits:
a) An electric cell is connected to a closed switch.
b) A battery is connected to an open
switch,
The switch is connected to a light globe, which
which is followed by two light globes in
is followed by an ammeter, then the circuit is
series. The second globe has a voltmeter
completed.
around it. The globes are followed by an
ammeter and the circuit is completed.
c) A powers supply is connected to two
fuses in parallel with each other. Each
fuse is controlled by its own switch.
One switch is open and the other is
closed. The circuit is completed and the
power source has a voltmeter around it
to measure the supplied voltage.
7. Describe voltage, resistance and current using analogies.
Provide an outline of voltage, resistance and current using analogies.




Voltage (V) – a measure of how much electrical energy is supplied to electrical particles
(electrons) moving through the circuit. It is correctly known as potential difference because it
measures a change in the potential (stored) energy of charge as it moves from one place to
another or through an electrical component. It can also be thought of as the pushing force on
charge. It is measured with a voltmeter and the standard unit it the volt (V).
Resistance (R) – a measure of a substances’ opposition to the flow of electric charge. All
substances have resistance, although some substances are more resistant than others. Substances
with relatively low resistances are known as conductors while those with fairly high resistances
are called insulators. The standard unit is the ohm (Ω) named after Georg Ohm.
Current (I) – a measure of the amount of electric charge passing a particular point in a circuit
every second. The direction of current flow in a circuit is defined as the direction a positive
charge would move (+ to -). It is measured with an ammeter and the standard unit is the Ampere
(A) named after Andre Ampere. (1 A = 6,000,000,000,000,000,000 electrons per second).
(Even though we know today that electric current is the flow of negative particles, scientists
many years ago believed it to be the flow of positive particles, however, the direction of current
is still for a positive particle. This is known as Conventional Current.)
The best analogy to use to describe these properties in relation to an electric circuit is to liken a
circuit to a water pump, ie.
Gauge to measure
difference in
pressure (voltmeter)
Water flow
Meter to measure
rate of flow
(ammeter)
Tap
Pump
-
The flow of water through the pipes is like the flow of electric charge in a
circuit.
The pump supplies the energy or pressure to force the water through the
pipes like a power supply to the electric charges.
The smaller section of pipes slows the flow of water and creates a pressure
difference (high to low) like an electrical resistor.
The tap controls flow like a switch.
The gauge measures the pressure difference just like a voltmeter measures
potential difference.
-
The meter measures the amount of water passing per unit time like an
ammeter measures the flow of electric charges.
8. Describe qualitatively the relationship between voltage, resistance and current.
Provide an outline of the relationship between voltage, resistance and current using descriptive
explanations.
The three variables voltage, resistance and current are all linked by a simple equation, ie.
V = IR

where: V = voltage (v)
I = current (A)
R = resistance (Ω)
This equation forms the basis of a physical law known as Ohm’s Law, which states: “the current
flowing through a conductor is proportional to the voltage difference between its ends”.
 Relating current to voltage and resistance shows that:
a) Current is directly proportional to voltage (similar effect).
b) Current is inversely proportional to resistance (opposite effect).

This can be shown mathematically as follows:
Say a voltage of 10V was
applied to a resistor of 5Ω,
then current flow would be:
I=
=
V
R
I=
V
R
I=
V
R
10
5
=
20
5
=
5
5
= 2A
The current is 2A.

Now suppose the voltage
This time the voltage is
was doubled while the
halved while the resistance
resistance was kept constant: is kept constant:
= 4A
The current is doubled.
= 1A
The current is halved.
Similarly it can be shown that the current is inversely proportional to the resistance of a conductor,
ie. Doubling the resistance halves the current and halving the resistance doubles the current.
Say a voltage of 10V was
applied to a resistor of 5Ω,
then current flow would be:
I=
=
Now suppose the resistance
was doubled while the
voltage was kept constant:
This time the resistance is
halved while the voltage
is kept constant:
V
R
I=
V
R
I=
10
5
=
10
10
=
= 2A
The current is 2A.
= 1A
The current is halved.
V
R
10
2 .5
= 4A
The current is doubled.
9. Compare advantages and disadvantages of series and parallel circuits
Select appropriate and relevant characteristics and describe ways in which the advantages and
disadvantages of series and parallel circuits are similar or different.
A series circuit is one in which all of the components are connected in line so that there is only
one pathway for the electric charges to flow. Eg.
One pathway for electricity

A parallel circuit is one in which all of the components are connected along separate pathways so
that the electric charges have more than one-way they can go. Eg.
Three pathways for electricity

These two types of circuits have advantages and disadvantages, ie. (the table below relates to the
two diagrams above with all globes being identical):
SERIES CIRCUITS
ADVANTAGES
The same amount of current flows through all
components.
Less wires are needed to connect all the
components.
PARALLEL CIRCUITS
ADVANTAGES
If one component breaks the others will still (if
one globe blows the others still glow).
Each component gets the same voltage (energy)
each glows with the same brightness.
Each globe can be operated by itself.
DISADVANTAGES
If one component breaks the whole circuit is cut,
thus if one globe blows none of them glow.
Each component uses some of the total voltage
(energy) thus the more globes added the dimmer
they become.
All components (globes) work at the same time.
DISADVANTAGES
Many more wires are needed to connect all the
components.
More current is needed each time a new
component (globe) is added due to more
pathways for the current to flow along.