### 1 - Maths and Science at Al Siraat

```Unit 7.3
Using circuits
Questions
Revision questions
Series circuits
1. Two globes are in series. What is the same and what is shared between
them?
1
The current is the same and the voltage is shared between them.
2 When a globe in a series circuit blows, the
others will:
A go out
B get brighter
C go duller
D stay the same.
2
A go out
Parallel circuits
3 Two globes are in parallel. What is the same and what is
shared between them?
3
Voltage is the same and the current is shared between them.
4 When a globe in a parallel circuit blows, the
others will:
A go out
B get brighter
C go duller
D stay the same.
4
D stay the same
Fairy lights
5 What is the effect of one globe blowing in a set of fairy lights wired in:
a parallel
b series?
5
a
parallel: no change
b
series: all will go out
6 How many 12-volt globes can operate at full power in a 240-volt series
circuit of fairy lights?
6
Twenty 12 V globes can operate at full power in a 240 V series
circuit of fairy lights (20 × 12 = 240).
More complex circuits
7 Does more current take the easy or hard path in a circuit?
7
More current takes the easy path in a circuit.
Household circuits
8 What voltage is household power?
8
Household power is 240 V.
9 Are the circuits in a house series or parallel?
9
Household circuits are parallel circuits.
10 Is household electricity AC or DC? Explain why.
10
Household electricity is AC because it is easier to generate and
transmit than DC.
When something goes wrong
11 What is a fuse and what does it do?
11
A fuse is a thin metal wire designed to melt when excessive current
flows through it, protecting the circuit.
12 List three ways of protecting a circuit and you from
damage.
12
fuses, circuit breakers, residual current detector (RCD)
13 When does an RCD cut the current to a circuit?
13
An RCD measures the current going into a circuit and the current
coming out of the circuit. If the circuit is ‘good’, then the current in and out will
be the same. If less current is coming out, then there is a current leak probably
caused by a short-circuit. The RCD then cuts the current to the circuit.
14 How does electrocution kill?
14
Electrocution kills by damaging your tissues and interfering with the
electrical signals that drive your heart.
15 List what you should do if you find a person who has
collapsed from electric shock.
15
Turn off the power. If this is not possible, do not touch the person directly.
Perhaps use an insulator such as a plastic rope or garden hose to move them away
from the source of electrocution. Then give first aid. Phone 000.
16 What is the emergency phone number from:
a a landline phone
b a mobile phone?
16
The emergency phone number is 000.
```