Electrical power & energy transfers

Energy resources are renewable or non-renewable.

Which two of the following energy resources are renewable?

Tick (✓) two boxes.

Biofuel

Coal

Nuclear

Oil

Wind

Figure 5 shows wind turbines in the countryside.

What are two effects on the environment of using wind turbines to generate electricity?

Tick (✓) two boxes.

Some birds are killed by wind turbines.

There is no fuel cost when using wind turbines.

Wind is an unreliable energy resource.

Wind turbines generate lots of electricity in windy conditions.

Wind turbines produce low frequency noise.

Figure 6 shows a wind turbine.

The useful power output of the generator in the wind turbine is 144 000 W.

The efficiency of the wind turbine is 0.30

Calculate the total power input to the wind turbine.

Use the equation:

Use the Physics Equations Sheet to answer Questions 05.4 and 05.5.

Which equation links current, potential difference and power?

Tick (✓) one box.

power = potential difference × current

The power output of the generator in the wind turbine is 144 000 W.

The potential difference across the generator is 960 V.

Calculate the current in the generator.

Figure 7 shows how the National Grid links the wind turbine to consumers.

The step-up transformer increases the potential difference and decreases the current.

What effect does decreasing the current have on the energy loss from the power cables?

Tick (✓) one box.

The energy loss decreases.

The energy loss is not affected.

The energy loss increases.

What is the function of the step-down transformer in Figure 7 ?

Tick (✓) one box.

To decrease the current.

To decrease the potential difference.

To decrease the power input.

A hairdryer contains a heating element and a motor.

The motor is connected to a fan.

Figure 2 shows part of the electrical circuit inside the hairdryer.

How does the current in the motor compare with the current in the heating element?

Give a reason for your answer.

Tick (✓) one box.

The current is greater in the motor.

The current in both components is the same.

The current is less in the motor.

The potential difference across the motor is 20 V.

What is the potential difference across the heating element?

Give a reason for your answer.

Tick (✓) one box.

20 V 50 V
210 V
230 V

The hairdryer transfers 460 000 J of energy in 250 seconds.

Calculate the power of the hairdryer.

Use the equation:

The current in the hairdryer is 8.0 A.

Calculate the time taken for 1200 C of charge to flow past a point in the hairdryer circuit.

Use the equation:

The hairdryer is connected to the mains electricity supply.

What is the frequency of the UK mains electricity supply?

Tick (✓) one box.

50 Hz 60 Hz
100 Hz
230 Hz

A cordless hairdryer contains a heating element and a fan.

The hairdryer is powered by a rechargeable battery.

Figure 10 shows the cordless hairdryer.

The power output of the heating element is 0.24 kW when the potential difference across the heating element is 16 V.

Calculate the current in the heating element.

Use the Physics Equations Sheet.

The battery of the hairdryer can be recharged from 0 to 100% in 6.0 hours.

The power input to the battery is 18 W.

The potential difference across the battery is 24 V.

Calculate the charge flow through the battery in 6.0 hours.

Use the Physics Equations Sheet.

A student investigated resistance in a circuit.

The student measured: the current in the resistor with an ammeter the potential difference across the resistor with a voltmeter.

Figure 3 shows a circuit diagram.

Which letter on Figure 3 shows the correct position for the ammeter to measure the current in the resistor?

Tick (✓) one box.

J K L

Draw the circuit symbol for a voltmeter in the box below.

The student changed the number of identical resistors in the circuit.

The student calculated the total resistance of the resistors.

Figure 4 shows the results.

Draw a line of best fit on Figure 4.

Predict the total resistance when 5 resistors were connected in the circuit.

You should extend your line of best fit.

How were the identical resistors connected in the student’s circuit?

Use Figure 4.

Tick (✓) one box.

The resistors were connected in parallel.

The resistors were connected in series.

The resistors were connected in series and in parallel.

Give a reason for your answer.

The potential difference across the battery was 3.0 V.

The maximum current in the circuit in the student’s investigation was 0.25 A.

Calculate the maximum power output of the battery in the student’s investigation.

Use the equation:

power = potential difference × current

A normal bicycle can be converted into an electric bicycle.

Figure 1 shows a converted bicycle.

Figure 2 shows the circuit diagram for the bicycle.

The circuit symbol for a motor is: M

The potential difference across the motor is 36 V.

The power output of the motor is 252 W.

Calculate the current in the motor.

Use the equation:

The bicycle battery can be recharged using the mains electricity supply.

A battery supplies direct current.

Mains electricity supplies alternating current.

Which graph shows an alternating current?

Tick (✓) one box.

A diode is used to change the alternating current to a direct current.

Which graph shows how the current in a diode varies with potential difference?

Tick (✓) one box.

The mean charging current from the mains is 5.0 A for 7200 seconds.

Calculate the charge flow to the battery.

Use the equation:

charge flow = current × time

Choose the unit from the box.

Calculate the work done in charging the battery when the power input is 1150 W for 7200 seconds.

Use the equation:

work done = power × time

A normal bicycle can be converted into an electric bicycle.

Figure 9 shows a converted bicycle.

Figure 10 shows the circuit diagram for the bicycle.

The circuit symbol for a motor is: M

The switch is used to turn the motor on or off.

Explain how the variable resistor is used to control the speed of the motor.

The battery can be recharged using the mains electricity supply.

The mains supply is alternating current.

Figure 11 shows a simplified version of the circuit that is used to recharge the battery.

Explain why charge only passes in one direction through the circuit.

The mains supply fully recharged the battery in 2 hours.

The mean charging current was 5.0 A.

The resistance of the battery was 0.18 Ω.

Calculate the energy dissipated due to the resistance of the battery in 2 hours.

Use the Physics Equations Sheet.

The cable connecting the kettle to the socket is a three-core cable.

The insulation on each wire is a different colour.

Draw one line from each wire to the colour of insulation.

Use the Physics Equations Sheet to answer questions 06.3 and 06.4.

Which equation links charge flow (Q), energy (E) and potential difference (V)?

Tick (✓) one box.

The kettle is switched on to heat some water.

The energy transferred to the heating element in the kettle is 260 000 J.

The potential difference across the heating element is 1.3 V.

Calculate the charge flow in the heating element.

Figure 17 shows a desk lamp connected to the mains electricity supply.

The desk lamp is fitted with a high-efficiency LED bulb.

What does ‘high-efficiency’ mean?

Tick (✓) one box.

A large proportion of the total energy input is destroyed.

A large proportion of the total energy input is usefully transferred.

A large proportion of the total energy input is wasted.

The LED bulb wastes energy as thermal energy.

How does the thermal energy affect the temperature of its surroundings?

The output power of the lamp is 2.8 W.

Calculate the energy transferred by the lamp in 60 seconds.

Use the equation:

energy transferred = power × time

Mains electricity can be dangerous.

Table 2 shows information about the effects of different electrical supplies on the human body.

ac is alternating current.

Compare the effects on the human body of 50 Hz ac with 10 000 Hz ac.

Use data from Table 2.

An oven is connected to the mains electricity supply using a three-core cable.

Figure 3 shows the three-core cable.

The insulation covering the earth wire has green and yellow stripes.

Give the colours of the insulation covering the live wire and the neutral wire.

A thermistor is used as part of a temperature sensor in the oven.

What is the circuit symbol for a thermistor?

Tick (✓) one box.

Figure 4 shows how the resistance of the thermistor in the oven varies with temperature.

Which statement describes the relationship shown in Figure 4 ?

Tick (✓) one box.

As temperature increases, resistance decreases.

As temperature increases, resistance stays the same.

As temperature increases, resistance increases.

Which temperature range shows the greatest decrease in the resistance of the thermistor?

Tick (✓) one box.

Between 50 and 100 °C

Between 100 and 150 °C

Between 150 and 200 °C

Between 200 and 250 °C

The resistance of the heating element in the oven is 5.0 Ω.

The current in the heating element is 12 A.

Calculate the power output of the heating element.

Use the equation:

power = (current)² × resistance

Calculate the energy transferred by the oven when 8000 C of charge flows through the heating element.

The potential difference across the heating element is 230 V.

Use the equation:

energy transferred = charge flow × potential difference

An LED on the oven is connected to an alternating current supply.

When the supply is switched on, the LED flashes on and off continuously.

Explain why.

A thermistor is used in an oven as part of a temperature sensor.

Draw the circuit symbol for a thermistor.

Figure 11 shows how the resistance of the thermistor varies with temperature.

Identify the temperature range when the thermistor is most sensitive to temperature change.

Tick (✓) one box.

Between 50 and 100 °C

Between 100 and 150 °C

Between 150 and 200 °C

Between 200 and 250 °C

The potential difference across the thermistor is 15 V.

The current in the thermistor is 0.015 A.

Calculate the energy transferred by the thermistor in 20 minutes.

The power output of the heating element in the oven is 0.72 kW.

The current in the heating element in the oven is 12 A.

Calculate the resistance of the heating element.

Ten-pin bowling is a game where a ball is rolled along the floor to knock over some wooden pins.

Figure 1 shows a person ten-pin bowling.

The speed of the ball was 8.0 m/s just after leaving the person’s hand.

The mass of the ball was 5.5 kg.

Calculate the kinetic energy of the ball.

Use the equation:

kinetic energy = 0.5 × mass × (speed)²

When the ball collides with the pins, energy is conserved.

What is meant by ‘conservation of energy’ when the ball collides with the pins?

Tick (✓) one box.

The gravitational potential energy of the pins is the same before and after the collision.

The kinetic energy of the ball is the same before and after the collision.

The total energy of the ball and pins is the same before and after the collision.

A machine returns the ball to the person.

The machine takes 25.0 s to return the ball to the person.

The useful power output of the machine is 660 W.

Calculate the work done by the machine in returning the ball to the person.

Use the equation:

work done = power × time

The machine has an efficiency of 0.60

The useful power output of the machine is 660 W.

Calculate the total power input to the machine.

Use the equation:

The machine has several moving parts.

What is the name of the force caused by the moving parts rubbing together?

What happens to the wasted energy from the machine?

Tick (✓) one box.

The wasted energy cools the surroundings.

The wasted energy heats the surroundings.

The wasted energy is destroyed.

Figure 11 shows a steam engine pulling a train.

One type of steam engine burns coal as the fuel source.

The energy from the coal is used to accelerate a train.

Describe how the energy stores of the coal and the train change as the train accelerates.

Which equation links energy (E), power (P) and time (t)?

Tick (✓) one box.

A steam engine has a power output of 8000 W.

Calculate the energy output of the steam engine in 3600 seconds.

In the 18th century the power output of steam engines was measured in a unit called ‘horsepower’.

Suggest why the unit of horsepower was used.

Figure 1 shows a steam engine pulling a train.

One type of steam engine burns coal as the fuel source.

The energy from the coal is used to accelerate a train.

Describe how the energy stores of the coal and the train change as the train accelerates.

Which equation links energy (E), power (P) and time (t)?

Tick (✓) one box.

A steam engine has a power output of 8000 W.

Calculate the energy output of the steam engine in 3600 seconds.

In the 18th century the power output of steam engines was measured in a unit called ‘horsepower’.

Suggest why the unit of horsepower was used.

A student investigated how the power output of a filament lamp varied with the current in the lamp.

Figure 15 shows part of the circuit the student used.

To calculate power output the student measured the current in the lamp and the potential difference across the lamp.

Complete Figure 15 by adding an ammeter and a voltmeter to make the measurements.

Use the correct circuit symbols.

Which energy store in the battery decreases when the lamp is switched on?

What happens to the energy transferred by the lamp?

Figure 16 shows the results.

Describe how varying the current affects the power output of the filament lamp.

Write down the equation which links current (I), power (P) and resistance (R).

Determine the resistance of the lamp when the current in the lamp is 0.22 A

A student investigated how the power output of a filament lamp varied with the current in the lamp.

Figure 1 shows part of the circuit the student used.

To calculate power output the student measured the current in the lamp and the potential difference across the lamp.

Complete Figure 1 by adding an ammeter and a voltmeter to make the measurements.

Use the correct circuit symbols.

Which energy store in the battery decreases when the lamp is switched on?

What happens to the energy transferred by the lamp?

Figure 2 shows the results.

Describe how varying the current affects the power output of the filament lamp.

Write down the equation which links current (I), power (P) and resistance (R).

Determine the resistance of the lamp when the current in the lamp is 0.22 A

Figure 3 shows how a power station supplies electricity to consumers.

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

Complete the sentences.

Choose answers from the box.

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

The step-up transformer causes the potential difference to increase and

the current to.

The use of the step-up transformer causes the energy transferred by heating

of the cables to.

The step-down transformer causes the potential difference to decrease and

the current to.

A nuclear power station has a power output of 350 000 000 W

Calculate the energy transferred by the power station in 60 seconds.

Use the equation:

energy transferred = power × time

Table 1 shows some of the waste products produced by three different types of power station.

Which type of power station contributes least to global warming?

Give a reason for your answer.

Which type of power station produces waste products that cause acid rain?

Give a reason for your answer.

Figure 9 shows how the National Grid connects power stations to consumers.

Explain how transformers are used in the National Grid.

A gas-fired power station has a power output of 50 MW

Calculate the energy transferred during 24 hours.

Table 5 shows some of the waste products produced by three different types of power station.

Evaluate the environmental impact of the power stations in Table 5.

Figure 9 shows a toaster.

A three-core cable connects the toaster to the mains electricity supply.

Which material could be used for the wires in the three-core cable?

Tick (✓) one box.

What is the potential of the earth wire?

Tick (✓) one box.

The wires and the cable are covered with a plastic material.

The plastic material covering each wire is a different colour.

Draw one line from each wire to the colour of the plastic material.

The plastic material covering the wires and cable is a type of polymer.

Explain how the plastic material acts as a safety feature if a person touches the cable.

When the toaster is switched on the current is 4.0 A

The resistance of the toaster is 60 Ω

Calculate the power of the toaster.

Use the equation:

power = (current)² × resistance

Give the unit.

Choose the unit from the box.

A student investigated the motor effect.

Figure 9 shows the apparatus used.

The student closed the switch and the wire moved.

Explain why.

Give two ways of reversing the direction of the movement of the wire.

Electric motors use the motor effect.

Energy is supplied to the electric motor by a battery.

The battery is charged using a charger.

When the charger is connected to the battery, the potential difference across the battery is 15.0 V

The total energy stored when the battery is fully charged is 0.81 MJ

The average current used to charge the battery is 3.00 A

Calculate the time taken to fully charge the battery.

The charger is plugged into the mains electricity supply.

This is an alternating supply.

Give two other properties of the UK mains electricity supply.

An energy input of 1.3 × 10¹⁸ J is supplied each year by power stations to the National Grid.

Not all of this energy is supplied to consumers. Some of the energy is wasted in the distribution process.

Write the equation which links efficiency, total input energy transfer and useful output energy transfer.

The energy supplied each year to consumers is 1.2 × 10¹⁸ J

Calculate the efficiency of the distribution process.

How is electrical power transmitted across the National Grid to make the process as efficient as possible?

Tick one box.

Write the equation which links energy transferred, power and time.

A wind turbine supplies a power output of 8000 kW for 1200 seconds.

Calculate the energy transferred by the wind turbine in kJ

Describe the environmental advantages and disadvantages of using wind turbines to generate electricity in the UK.

An energy input of 1.3 × 10¹⁸ J is supplied each year by power stations to the National Grid.

Not all of this energy is supplied to consumers. Some of the energy is wasted in the distribution process.

Write the equation which links efficiency, total input energy transfer and useful output energy transfer.

The energy supplied each year to consumers is 1.2 × 10¹⁸ J

Calculate the efficiency of the distribution process.

How is electrical power transmitted across the National Grid to make the process as efficient as possible?

Tick one box.

Write the equation which links energy transferred, power and time.

A wind turbine supplies a power output of 8000 kW for 1200 seconds.

Calculate the energy transferred by the wind turbine in kJ

Describe the environmental advantages and disadvantages of using wind turbines to generate electricity in the UK.