Energy Transfers (AQA GCSE Physics): Exam Questions

Figure 3 shows a battery powered drone.

Figure 3

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.

The drone can fly for 22 minutes before it needs to be recharged.

Write the equation linking power (P), energy (E) and time (t).

Calculate the power of the drone.

Calculate the current through the drone while it is flying.

Calculate the resistance of the drone.

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

Figure 4

Explain what is meant by the term ‘ac’.

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

Figure 5

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

Calculate the power output of the kettle.

Write the equation that links current (I), charge flow (Q) and time (t).

Calculate the current through the kettle when 417 coulombs of charge flow through the kettle in 1.0 minute.

Calculate the resistance of the kettle.

Give your answer to 2 significant figures.

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

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

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

Calculate the output voltage of one turbine.

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.

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

Table 1

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

Give your answers to 2 significant figures.

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

   Work done = .................................... J

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

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

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

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

Which statements are true about step-down transformers?

Tick (✓) three boxes.   

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

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

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

Determine the percentage efficiency of the cables.

Give your answer to the nearest whole percent.

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

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

Table 1

Calculate the total resistance of the circuit in the washing machine.

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

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

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

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