Edexcel GCSE Physics

Topic Questions

GCSEPhysicsEdexcelTopic Questions10. Electricity & Circuits10.3 Energy Transfers in Circuits

10.3 Energy Transfers in Circuits

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1a
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State the definition of power and its unit.

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1b
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State the equation linking power, current and potential difference.

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1c
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An electric kettle is connected to a mains voltage of 230 V.

The power of the kettle is 2860 W.

 

Calculate the current in the kettle.

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1d
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The kettle boils for 2.5 minutes.

 

Calculate the energy transferred to the kettle during this time.

 

Use an equation selected from the list of equations given on your exam paper.

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2a
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An immersion heater is an electrical device used to heat up water.

A resistor is in the immersion heater shown in Figure 1 with a resistance of 0.68 Ω.

10-3-e-2a-immersion-heater-and-battery

Figure 1

The power of the immersion heater is 142 W. 

Calculate the current through the element in the immersion heater.

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2b
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The resistor becomes warm while there is current in it.

Explain, in terms of particles in the wire, why the resistor becomes warm.

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2c
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State the energy transfers in the resistor when it becomes warm.

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2d
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State the dangers of overheating the resistor and explain how this can be reduced.

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3a
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State the equation linking power, energy transferred and time.

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3b
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What is the unit Watts (W) equivalent to?

square   A   J/A

square   B   J/s2

square   C   J/s 

square   D   J/V

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3c
Sme Calculator2 marks

Table 1 shows the power rating for some domestic electrical appliances.

Table 1

Electrical Appliance Power (W)
Kettle 2400
Clock 10
Lamp 50
Iron 1250

i)
State which appliance transfers stored energy to other types of energy at the fastest rate.

[1]

ii)
State which appliance transfers stored energy to other types of energy at the slowest rate.
[1]

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1a4 marks

This question is about using the mains electricity supply.

(i)
An electric kettle is used to boil some water.
The mains supply voltage is 230 V.
The power supplied to the kettle is 1.9 kW.

Calculate the current in the kettle.
Use the equation

straight I space equals space straight P over straight V

[2]

current supplied to the kettle = .............................................................. A

(ii)
A coffee machine takes 120 s to heat some water.

Mains supply voltage = 230 V.
Current in this coffee machine = 7.4 A

Calculate the energy transferred to the coffee machine in 120 s.

Use an equation selected from the list of equations at the end of the paper.

[2]

energy transferred to coffee machine = .............................................................. J

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1b3 marks

Figure 10 shows the inside of a mains plug.

The neutral wire is labelled.

fig-10-paper2f-oct2021-edexcel-gcse-physics

Figure 10

(i)
State the name of wire X and the name of wire Y.

[2]
wire X ..............................................................
wire Y ..............................................................

(ii)
State the name of component Z.

[1]
component Z ..............................................................

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1c3 marks

A transformer is used to connect a laptop computer to the mains electricity supply.


The input voltage to the transformer is 230 V.

The output current from the transformer is 2.37 A.

The transformer has an output voltage of 19.0 V.

Calculate the input current to the transformer.

Use the equation

input current × input voltage = output current × output voltage

input current = .............................................................. A

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2a6 marks

A technician investigates different electrical devices that are used in a car.

The technician connects a device to the 12 V car battery.

The technician measures the current in the circuit and the potential difference (voltage) across the device.

Figure 17 shows the car battery and the device that is being tested.

fig-17-paper2h-oct2021-edexcel-gcse-physics

Figure 17

(i)
Draw on Figure 17 to show how the circuit should be completed so that the current in the circuit and voltage across the device can be measured.

[2]

(ii)
The technician tests a headlamp.

The current in the headlamp is 4.8 A when connected to the 12 V battery.
 
Calculate the power supplied to the headlamp.

[2]

power = .............................................................. W

(iii)
The technician tests an interior light.

The current in the interior light is 600 mA when connected to the 12 V battery.

Calculate the energy transferred to the interior light in 7 minutes.

Use an equation selected from the list of equations at the end of the paper.

[2]

energy transferred = .............................................................. J

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2b5 marks

The technician connects four devices to the car battery.

Each device is connected to its own switch and its own fuse.

Figure 18 shows how the four devices, fuses and switches are connected.

The current in each device is shown next to the device.

fig-18-paper2h-oct2021-edexcel-gcse-physics

Figure 18

(i)
Calculate the current in the wires to the battery when all the devices are switched on.

[1]

current = .............................................................. A

(ii)
State how the overall resistance of the circuit changes when any one of the devices is switched off.

[1]

(iii)
There is a current of 2.3 A in the radio when the radio is working correctly.

Which of these should the technician choose to protect the radio circuit?

[1]
  ☐ A 2 A fuse
  ☐ B 5 A fuse
  ☐ C 10 A fuse
  ☐ D 13 A fuse

(iv)
Explain why the wires to the battery in a car are thicker than the wires that connect each device to its switch and its fuse.

[2]

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3a1 mark

Figure 12 shows a graph of current against potential difference for an electrical component.


fig-12-paper2f-june2018-edexcel-gcse-physics
Figure 12

Which electrical component will show this variation of current with potential difference?


  ☐ A thermistor
  ☐ B low value resistor at constant temperature
  ☐ C high value resistor at constant temperature
  ☐ D diode

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3b6 marks

A lamp is connected to a potential difference of 0.24 V.

The current in the lamp is 0.12 A.

 
(i)
Calculate the power of the lamp.
Use the equation

      P = I × V
[2]


power of the lamp = ............................................... W
 
(ii)
The potential difference is changed to 0.30 V.
The current in the lamp is now 0.13 A.

The lamp is switched on for 35 s.

Calculate the energy that is transferred in this time.
Select an equation from the list of equations at the end of this paper.

[2]


energy transferred = ............................................... J

(iii)
The current in the lamp stays at 0.13 A.

Calculate the charge that flows through the lamp in 35 s.
Use the equation

    Q = I × t
[2]

charge = ............................................... C

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3c3 marks

A student measures the current in the lamp for several values of potential difference across the lamp.

Figure 13 shows the student’s results.

potential difference across
the lamp in volts (V)		 current through the lamp
in amps (A)
0.06 0.05
0.12 0.08
0.18 0.10
0.24 0.12
0.30 0.13
0.36 0.13


Figure 13

The student uses the results in Figure 13 to write this conclusion.

‘As the potential difference across the lamp increases, the current in the lamp increases and the relationship is directly proportional.’

Comment on the student’s conclusion.

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4a4 marks

Table 1 shows a range of household appliances and their power ratings.

Appliance Power rating Current drawn
Desk lamp 14 W  
55 inch OLED TV 125 W  
Toaster  480 W  
Microwave 900 W  

Table 1 

Complete Table 1 by adding the values for the current drawn for each appliance.

Give your answers to 2 significant figures.

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4b3 marks
Calculate the electrical work done by using the toaster on full power for 3 minutes.

   

   

work done = .................................... J

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4c3 marks

Calculate the amount of charge that flowed through the toaster circuit during the 3 minutes of use.

Give your answer to 2 significant figures.

   

   

charge = .................................... C

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4d2 marks

The toaster is not 100% efficient. 

Using the idea of energy transfers, explain why the toaster is not 100% efficient and state where this wasted energy is transferred to.

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5a4 marks

During one year, 2.42 × 1019 J of energy was transferred from National Grid.

Calculate the power rating of the National Grid.

Give your answer in kW to 1 significant figure.

   

power = .................................... kW

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5b2 marks

A step-up transformer sends a current of 63 A at a potential difference of 400 000 V through the transmission cables of the National Grid.

The transmission cables have a resistance of 200 Ω.

Calculate the power dissipated from the heating of the cables.

   

power dissipated = .................................... W

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5c3 marks

Determine the maximum potential power leaving the step-up transformer.

   

   

power = .................................... W

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5d2 marks

Determine the percentage efficiency of the cables.

Give your answer to the nearest whole percent.

   

   

efficiency = .................................... %

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