OCR GCSE Combined Science
Topic questions Electricity Electrical charge & current
17 questions · 69 marks · about 1.5 hours
A lamp is turned on for 100 s.
The charge flowing is 12 C.
The current is then doubled. The time the lamp is turned on is doubled.
What is the charge flowing now?
Use the equation: charge flow = current × time
A 6 C
B 12 C
C 24 C
D 48 C
A mobile phone is charged for 3 hours. The mean charging current is 0.15 A.
What is the charge transferred to the mobile phone in this time?
Use the equation: charge flow = current × time
A 0.45 C
B 27 C
C 540 C
D 1620 C
A student does a practical investigation to find the charge transferred when a laptop is charged.
Which equipment must they use?
A Ammeter only
B Ammeter and stopwatch
C Voltmeter only
D Voltmeter and stopwatch
This question is about how electrical circuits work.
A student builds three different electrical circuits.
Explain why the lamp does not light in each circuit.
Fig. 12.1 shows the first circuit.
Fig. 12.1
The lamp does not light because........
Fig. 12.2 shows the second circuit.
Fig. 12.2
The lamp does not light because........
Fig. 12.3 shows the third circuit.
Fig. 12.3
The lamp does not light because........
The student uses the meters in the circuit in Fig. 12.4 to determine the resistance of a resistor.
Fig. 12.4
The student uses the circuit to take several readings of current and potential difference. The graph shows the student’s results.
Complete the sentence about the graph to explain the relationship between potential difference and current. Use words from the list.
decreases increases stays the same
As the potential difference increases, the current........
The ratio of potential difference: current at 3 V is 15: 1.
Calculate the ratio of potential difference: current at 6 V. Use the graph.
Complete the sentence about the graph. Use a word from the list.
elastic linear non-linear plastic
The graph of current against potential difference for the resistor is........
This diagram shows a cell connected in series with a resistor.
Calculate the potential difference of the cell in the diagram.
Use the equation: potential difference = current × resistance
Fig. 16.1 shows a heater plugged into an electrical socket.
Fig. 16.1
The heater is operating normally.
What are the names of the two wires in the plug that carry a current?
Tick (✓) one box.
A live wire is accidentally connected to the earth wire in the house. This causes a large current to flow in the earth wire.
This can cause electrocution.
Suggest another reason why this is dangerous.
A 2.4 kW heater is used for 2.5 hours each day for 1 week.
Calculate the energy transferred in kW h by the heater in 1 week.
Use the equation: energy transferred = power 
time
Energy transferred in 1 week =........ kW h
A residual current device (RCD) is a safety feature found in homes.
The RCD turns off the electricity quickly if it detects a fault due to a difference between the current in the live wire and the current in the neutral wire.
Fig. 16.2 shows the effects that mains current has on a human body.
Fig. 16.2
Current passing through a human body (mA)
Describe one trend shown by Fig. 16.2.
A current of 10 mA is passing through a human body.
How long can the current pass through the body before the person has difficulty breathing?
Calculate the charge flowing when 150 mA is in the human body for 0.3 s.
Use the equation: charge flow = current 
time
Sensitive RCDs are designed to shut off the electricity supply within 40 ms.
Suggest why this is an important feature for currents below 200 mA. Use Fig. 16.2.
An electrician has a choice of two different RCDs, A and B, to use in a house.
| RCD A | RCD B | |
| Minimum difference in current needed between the live wire and neutral wire before electricity turns off (mA) | 10 | 30 |
| Time taken to turn off electricity (ms) | 100 | 40 |
Suggest which RCD the electrician should use in the house.
Give two reasons. Use Fig. 16.2.
Fig. 11.1 shows a heater plugged into an electrical socket.
Fig. 11.1
The heater is operating normally.
What are the names of the two wires in the plug that carry a current?
Tick (✓) one box.
A live wire is accidentally connected to the earth wire in the house. This causes a large current to flow in the earth wire.
This can cause electrocution.
Suggest another reason why this is dangerous.
A 2.4 kW heater is used for 2.5 hours each day for 1 week.
Calculate the energy transferred in kW h by the heater in 1 week.
Use the equation: energy transferred = power time
Energy transferred in 1 week =........ kW h
A residual current device (RCD) is a safety feature found in homes.
The RCD turns off the electricity quickly if it detects a fault due to a difference between the current in the live wire and the current in the neutral wire.
Fig. 11.2 shows the effects that mains current has on a human body.
Fig. 11.2
Current passing through a human body (mA)
Describe one trend shown by Fig. 11.2.
A current of 10 mA is passing through a human body.
How long can the current pass through the body before the person has difficulty breathing?
Calculate the charge flowing when 150 mA is in the human body for 0.3 s.
Use the equation: charge flow = current time
Sensitive RCDs are designed to shut off the electricity supply within 40 ms.
Suggest why this is an important feature for a current of 200 mA. Use Fig. 11.2.
An electrician has a choice of two different RCDs, A and B, to use in a house.
| RCD A | RCD B | |
| Minimum difference in current needed between the live wire and neutral wire before electricity turns off (mA) | 10 | 30 |
| Time taken to turn off electricity (ms) | 100 | 40 |
Suggest which RCD the electrician should use in the house.
Give two reasons. Use Fig. 11.2.
A student builds the circuit shown in the diagram. W, X, Y and Z are points in the circuit.
Calculate the potential difference between Y and Z.
Use the Equation Sheet.
The resistance of the circuit between Y and Z must be less than 10 
.
Explain why.
Calculate the current at W.
Which statement describes the values of the current at W and X ?
Tick (✓) one box.
Calculate the power dissipated by one of the 10 
resistors.
Use the Equation Sheet.
A 6 V battery provides a current of 0.4 A in a circuit for 20 seconds.
How much energy is transferred by the battery?
Use the equations: charge flow = current × time
energy transferred = charge × potential difference
A 0.12 J
B 0.75 J
C 15 J
D 48 J
In an electrical circuit, a current of 1.2 A flows for 25 seconds.
How much charge is transferred?
A 0.048 C
B 20.8 C
C 30 C
D 1800 C
Which row of the table describes charge and current?
| Charge | Current | |
| A | A property of all matter | The energy supplied per coulomb |
| B | A property of all matter | The rate of flow of charge |
| C | Resistance to current flow | The energy supplied per coulomb |
| D | Resistance to current flow | The rate of flow of charge |
Which row of the table is correct?
Use the equation: charge flow = current 
time
| Current (A) | Time (s) | Charge flow (C) | |
| A | 1.0 | 2.0 | 0.5 |
| B | 1.0 | 2.0 | 2.0 |
| C | 3.0 | 1.5 | 2.0 |
| D | 3.0 | 2.0 | 0.6 |
Which circuit gives a flow of charge?
A student connects this electrical circuit. The resistors are identical.
Ammeter A1 reads 1.6 A when the switch S is open.
What does ammeter A2 read when switch S is closed?
A 0.0 A
B 0.8 A
C 1.6 A
D 3.2 A
A current of 2.5 A flows for 1 minute through a circuit.
Calculate the charge flowing.
Use the equation: charge flow = current × time
A 0.04 C
B 2.5 C
C 24 C
D 150 C
What is the current at point Q in the circuit?
A teacher demonstrates static electricity using a Van de Graaff generator.
She places 3 metal foil containers on top of the dome of the Van de Graaff generator. When the Van de Graaff generator is turned on, the foil containers fly off the dome one by one.
Explain why this happens.
Use ideas about charge in your answer.
Calculate how long it would take for a charge of 5.0 C to flow with a current of 25 mA.
Use the equation: Charge flow = Current × Time
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