Energy Transfers (AQA GCSE Physics)

Exam Questions

2 hours13 questions
1a1 mark

Figure 2 shows a toaster. The toaster uses electric current to heat bread.

Figure 2

fig-2-2-3-easy-aqa-gcse-physics

The toaster has a metal case.

Why would it be dangerous for the live wire from the electric cable to touch the case of the toaster?

1b3 marks

The toaster uses mains power to function.

A label on the toaster says that the power output of the toaster is 1.5 kW.

Calculate the current in the toaster.

1c3 marks
Calculate the resistance of the toaster.

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2a1 mark

Electrical power is supplied to homes and businesses via the National Grid.

What is the National Grid?

Tick (✓) one box.

A system of cables and transformers linking power stations to consumers begin mathsize 36px style square end style
A system of cables and pylons linking power stations to consumers size 36px square
A system of cables linking power stations to consumers  size 36px square
2b3 marks

Figure 1 shows a simplified diagram of the National Grid.

Figure 1

2-3-e-2b-national-grid

Write the names of the components labelled X, Y and Z.

2c2 marks

Which statements are true about the use of a step-up transformer in transmitting power through the cables of the National Grid?

Tick (✓) two boxes.

   

Higher potential difference means lower current begin mathsize 36px style square end style
Higher potential difference means less wasted energy size 36px square
Lower potential difference means lower current  size 36px square
Lower potential difference means less wasted energy size 36px square

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3a1 mark

Which are the correct units for power?

Tick (✓) one box.

   

 J begin mathsize 36px style square end style
C  size 36px square
W size 36px square
A size 36px square
V size 36px square
3b1 mark

State the equation linking power, current and potential difference.

3c2 marks

Calculate the power rating of an electric heater that plugs into the mains supply and draws a current of 13 A.

   

   

Power = .................................... W

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4a1 mark

Which arrangement is correct for the equation linking power, current and resistance?

Tick (✓) one box.

   

P space equals space I R begin mathsize 36px style square end style
P space equals space I over R size 36px square
P space equals space I R squared size 36px square
P space equals space I squared R  size 36px square
4b3 marks

A current of 3.6 A passes through a 20 Ω resistor.

Calculate the power transferred to the resistor.

Give your answer to 2 significant figures.

   

   

Power (2 significant figures) = .................................... W
4c3 marks

Complete the sentences. 

Choose answers from the box. 

Each answer can be used once, more than once or not at all.

chemical

gravitational

electrons

protons

magnetic

thermal

 

     

When charge flows through a resistor, the .............................. collide with the metal ions of the resistor.

   

Energy is transferred to the .............................. store of the metal ions and they vibrate faster.

   

Energy in the  .............................. store of the cell decreases as work is done to move the charge around the circuit.

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5a6 marks

A homeowner buys an electrical heater with a maximum power rating of 2000 W.

She wants to know if it uses more energy to put the heater on full power for 1 hour or to put it on half power for 2 hours.

Show that the energy transferred in both cases will be the same.

5b3 marks

Complete the sentences describing the energy transfers taking place in the electric heater. 

Choose answers from the box. 

Each answer can be used once, more than once or not at all.

thermal

magnetic

electrically

mechanically

gravitational

nuclear

     

Energy is transferred .............................. from the mains supply.

   

Energy is transferred to the  .............................. store of the heating element.

   

Energy is transferred to the  .............................. store of the surrounding air in the room.

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1a2 marks

Figure 3 shows a battery powered drone.

Figure 3

fig-3-2-3-medium-aqa-gcse-physics

The battery for the drone is marked as 1300 mAh. 

This means that it could supply a current of 1300 mA for 1 hour.

Battery voltage = 14.8 V

Show that the energy stored in the battery is about 70 kJ.
1b1 mark

The drone can fly for 20 minutes before it needs to be recharged.

State the equation linking power (P), energy (E) and time (t).
1c2 marks
Calculate the power of the drone.
1d3 marks
Calculate the current that flows through the drone while it is flying.
1e3 marks
Calculate the resistance of the drone.

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2a2 marks

The electric kettle in Figure 4 below uses the ac mains electricity supply.

Figure 4

fig-4-2-3-medium-aqa-gcse-physics

Explain what is meant by the term ‘ac’.
2b2 marks

The graph in Figure 5 below shows how the energy transferred by the kettle changes with time.

Figure 5

fig-5-2-3-medium-aqa-gcse-physics

The gradient of the graph gives the power output of the kettle.

Calculate the power output of the kettle.

2c1 mark
State the equation that links current (I), charge flow (Q) and time (t).
2d3 marks
Calculate the current through the kettle when 417 coulombs of charge flow through the kettle in 1 minute.
2e4 marks

Calculate the resistance of the kettle.

Give your answer to 2 significant figures.

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3a3 marks

A wind turbine converts kinetic energy in the wind to electrical energy, which it then transfers to the National Grid.

The wind farm in Figure 5 below contains 5 wind turbines, each with an average power output of 3 MW.


Figure 6

fig-6-2-3-medium-aqa-gcse-physics

Calculate the total energy generated by the wind farm in 30 minutes.

Show all your working.

3b3 marks

In a single turbine, the current through the generator is 450 A.

Calculate the output voltage of one turbine.

3c4 marks

A step up transformer is used to increase the output voltage to 132 kV for transmission.

Explain why the voltage is stepped up in this way.

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4a4 marks

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

Table 1

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

 

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

Give your answers to 2 significant figures.

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

   

   

Work done = .................................... J
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 (2 significant figures) = .................................... C

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5a1 mark

The National Grid is a system of transformers and cables that connects power stations to consumers. 

Figure 1 shows a simplified diagram of the National Grid.


Figure 1

2-3-e-2b-national-grid

State which transformer, X or Y, is the step-up transformer.

5b3 marks

The transmission cables in Figure 1 have a current of 63.2 A at a potential difference of 400 000 V when travelling between the two transformers.

The resistance of the cable is 200 Ω.

Calculate the power transferred in heating up the cable.

   

   

Power = .................................... W
5c3 marks

Which statements are true about step-down transformers?

Tick (✓) three boxes.

   

Have more turns on the primary coil begin mathsize 36px style square end style
Have more turns on the secondary coil size 36px square
Used to decrease the potential difference  size 36px square
Used to increase the potential difference size 36px square
Used to reduce wasted energy in transmission size 36px square
Used to make energy supplied to houses safer size 36px square

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1a2 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
1b3 marks
Determine the maximum potential power leaving the step-up transformer.

   

   

Power = .................................... W
1c2 marks

Determine the percentage efficiency of the cables.

Give your answer to the nearest whole percent.

   

   

Efficiency = .................................... %

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2a4 marks

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

Table 1

Appliance Power rating
Washing machine 2200 W
55 inch LED TV 125 W
Kettle 2500 W
Microwave 1000 W

 

Calculate the total resistance of the circuit in the washing machine.
2b4 marks

The kettle in Table 1 takes two minutes to boil a mug of cold water from the tap. 

Determine how long it would take to boil a mug of tap water in the microwave.

   

   

Time taken = .................................... s
2c3 marks

The cost of electricity is 37 p per kilowatt hour (kW hr)

Calculate the cost of using the TV in Table 1 for 4 hours.

   

   

Cost = .................................... p

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3a4 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
3b5 marks
Some houses use solar cells to generate electricity.

When the energy generated by the solar cells is not needed, the energy is stored in a battery. 

A house has solar cells on the roof. 31 000 C of charge flows through the cable from the solar cells to the battery in a 24 hour period.

The potential difference in the circuit is 3.3 V.

Determine the power lost due to heating in the cable.

Give your answer to 2 significant figures.

   

   

Power = .................................... W

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