P2.3a Matching symbols
The cards show different parts of a circuit. Match up the pictures to the circuit symbols,
the names and the descriptions of what they do.
© Pearson Education 2011. Edexcel GCSE Additional Science Activity Pack
This document may have been altered from the original.
P2.3b Currents and calculations
A cell pushes electrons around a circuit. The movement of charged electrons that it produces is a direct
current.
The relationship between charge, current and time can be written as:
charge (in coulombs, C) = current (in amps, A) × time (in seconds, s)
The equation can be rearranged to give these versions:
current =
charge
time
time =
charge
current
Example
800 C of charge passes through a resistor. The current is 4 A. How long does it take for the charge to
pass?
Choose the equation you need. You are asked to calculate time, so use the equation that starts with
time:
time =
charge
current
Put the numbers in:
time =
800 C
4A
= 200 s
1
What is the difference between a direct current and an alternating current?
2
A bulb has a current of 4 A flowing through it. It is switched on for 20 s. How much charge flows
through it?
3
A hairdryer has a current of 3.6 A flowing through it. It is switched on for 60 s. How much charge
flows through it?
4
What is the current when 750 C of charge flows through an electric fire in 1 minute? (Hint: remember
that 1 minute = 60 s).
5
How long does it take for 4000 C of charge to flow through a light bulb if the current is 2 A?
© Pearson Education 2011. Edexcel GCSE Additional Science Activity Pack
This document may have been altered from the original.
P2.3c Charges and currents
The relationship between charge, current and time can be expressed as:
charge (Q)
= current (I)
×
time (t)
(in coulombs, C) (in amps, A) (in seconds, s)
1
Find the charge that passes through each of the following devices:
a a bulb that has a 4.5 A current flowing through it for 20 s
b a hairdryer that has a current of 3.6 A flowing through it for 1 minute
c an oven that has a current of 22 A flowing through it for 30 minutes.
2
A current of 4 A flows through a component so that 800 C passes through it. For how many seconds
must the current be flowing for this to be true?
3
What is the current in the following cases?
a 90 000 C of charge flows through an electric fire in 2 hours.
b 9000 C of charge flows through a light bulb in 5 hours.
4
These students are thinking about how
fast electrons move in a wire.
Read the description of Jenny watering
the garden. This can be used as a model
to help you to think about how fast
electrons travel.
The light comes on as soon
as you press the switch.
The electrons must be
travelling really fast to
get from the switch to
the bulb so quickly!
Surely they can’t
travel that quickly?
Jenny was
watering the garden. She unrolled the hosepipe, and got her little brother to
turn the tap on for her. It seemed to take ages for the water to come out!
She had watered half of the garden when the phone rang, so she turned the
tap off and went indoors. When she started watering again, the water came
out of the hosepipe as soon as she turned the tap on.
a Why didn’t water come out of the end of the hosepipe as soon as her brother turned the tap on?
b Why did it come out as soon as the tap was turned on the second time?
5
Use the story of Jenny as a model to help you to explain why a light comes on as soon as you press
the switch, without the electrons having to move very fast.
6
Electrons in a wire actually move at a speed of around 1 mm per second. Calculate how many
minutes it would take for an electron in a direct current to travel from a switch to a light bulb that is
3 metres away.
Extra challenge
7
An electronic component uses a current of 1.5 A when it is working, and 20 nA when it is on
standby. How long does it take for 1 C of charge to flow through the component:
a when it is operating
b when it is on standby?
(1 A = 1 microamp = 10–6 A and 1 nA = 1 nanoamp = 10–9 A).
© Pearson Education 2011. Edexcel GCSE Additional Science Activity Pack
This document may have been altered from the original.