Electrical power & energy transfers

Figure 2 shows circuit symbols for some electrical components.

A student connects a circuit to measure the current in a filament lamp.

The student uses:

• an ammeter

• a cell

• a filament lamp.

Draw a circuit diagram for a circuit the student could use to measure the current in a filament lamp.

You should use three of the circuit symbols from Figure 2.

Which component is the source of energy for the circuit?

Tick () one box.

There is a current of 1.5 A in the filament lamp for a time of 30 s.

Calculate the charge flow in the filament lamp.

Use the equation:

charge flow = current × time

The current in the filament lamp is 1.5 A when the potential difference across the filament lamp is 12 V.

Calculate the resistance of the filament lamp.

Use the equation:

Choose the unit from the box.

Figure 3 shows how the current varies with potential difference for the filament lamp.

Describe the relationship between potential difference and current for the filament lamp.

As the current in the filament lamp increases, the temperature of the filament lamp increases.

What happens to the resistance of the filament lamp as the temperature increases?

In most homes, filament lamps have been replaced with LED bulbs.

Table 1 shows information about a filament lamp and an LED bulb.

Explain the advantages of using LED bulbs instead of filament lamps.

You should include a calculation in your answer.

Figure 5 shows a plastic kettle.

The kettle is connected to the mains electricity supply.

What is the frequency of the UK mains electricity supply?

Tick () one box.

The cable that connects the kettle to the plug contains two insulated wires.

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

Use the Physics Equations Sheet to answer questions 04.3 and 04.4.

Write down the equation that links current (I), potential difference (V) and power (P).

The power of the heating element in the kettle is 2100 W.

The potential difference across the heating element is 230 V.

Calculate the current in the heating element.

Give your answer to 2 significant figures.

The kettle is designed to switch off when the water reaches boiling point.

Before the kettle switches off, 0.0080 kg of water changes state.

The energy transferred to change the state of the water is 18 000 J.

Calculate the specific latent heat of vaporisation of the water.

Use the Physics Equations Sheet.

Specific latent heat of vaporisation = J/kg

A different kettle is used to heat some water.

The useful output energy transferred to the water is 75 600 J.

The total input energy transferred by the kettle is 84 000 J.

Calculate the efficiency of the kettle.

Use the equation:

Explain one advantage of electrical appliances having a high efficiency.

A student investigated the resistance of a resistor.

The student used:

• the resistor

• a cell

• a switch

• an ammeter

• a voltmeter.

Draw a circuit diagram for a circuit the student could use to measure the resistance of the resistor.

The student:

• added a variable resistor to the circuit

• used the variable resistor to change the readings on the ammeter and the voltmeter

• recorded several different pairs of readings from the ammeter and the voltmeter.

When the reading on the ammeter was 450 mA, the reading on the voltmeter was 2.7 V.

Calculate the resistance of the resistor.

Use the Physics Equations Sheet.

The student plotted a graph of current against potential difference for the fixed resistor.

Complete Figure 2 to show a sketch graph for a fixed resistor at a constant temperature.

Figure 2

Figure 3 shows five resistors with the same resistance but different power ratings.

The power rating of a resistor is the maximum energy the resistor can transfer each second without overheating.

Each resistor has a resistance of 2.2 kΩ.

Determine which resistors in Figure 3 are suitable to be used in a circuit that has a maximum current of 0.012 A.

Use the Physics Equations Sheet.

Figure 5 shows a laptop computer, and a charger plugged into the mains supply.

Give the potential difference and frequency of the UK mains electricity supply.

The cable that connects the charger to the plug contains two wires that have coloured insulation.

The cable does not contain an earth wire.

Name each wire in the cable.

Give the colour of the insulation covering each wire.

Name of wire Colour of insulation

The input to the charger is an alternating potential difference.

The output from the charger is a direct potential difference.

Describe the difference between an alternating potential difference and a direct potential difference.

A student is using the laptop computer.

The student notices that the battery has no stored energy.

The student quickly plugs the charger into the laptop and continues to use the laptop.

The laptop charger provides a constant power to the laptop.

The laptop takes longer to charge when the student uses the laptop than when the laptop is not used.

Explain why.

The potential difference across the laptop circuit is 15 V.

The average current in the laptop circuit when it is being used is 4.8 A.

The laptop charger provides a constant power of 97 W.

The maximum energy that the battery can store is 225 kJ.

Calculate the time taken to fully charge the battery from zero when the laptop is used continuously.

Use the Physics Equations Sheet.

Give your answer in hours.

Figure 1 shows a circuit diagram. The circuit contains a battery and two lamps, X and Y.

How does the current in lamp X compare with the current in lamp Y ?

Tick (✓) one box.

Lamp X and lamp Y are not identical.

The potential difference across the battery is 4.5 V.

The potential difference across lamp X is 1.5 V.

Calculate the potential difference across lamp Y.

The current in lamp X is 1.2 A.

The potential difference across lamp X is 1.5 V.

Calculate the power of lamp X.

Use the equation:

power = potential difference × current

Calculate the resistance of lamp X.

Use the equation:

The current in lamp X is 1.2 A.

Calculate the charge flow through lamp X in 40 seconds.

Use the equation:

charge flow = current × time

The switch can be used to turn the lamps on and off.

Immediately after the lamps are switched on, the resistance of each lamp increases.

Why does the resistance of each lamp increase?

Tick (✓) one box.

Figure 1 is repeated below.

Lamp Y breaks.

What happens to lamp X ?

Give a reason for your answer.

Tick (✓) one box.

Figure 10 shows an electric whisk that plugs into the mains electricity supply.

The whisk can mix food by spinning a beater.

Give two energy stores that increase when the whisk is switched on.

Use the Physics Equations Sheet to answer questions 06.2 and 06.3.

Work is done by the whisk when it is used to mix food.

Write down the equation that links power (P), time (t) and work done (W).

The power output of the whisk is 92 W.

Calculate the time for the whisk to do 23 000 J of work.

Use the Physics Equations Sheet to answer questions 06.4 and 06.5.

Which equation links current (I), power (P) and resistance (R)?

Tick (✓) one box.

The current in the whisk is 500 mA.

The resistance of the whisk is 640 Ω.

Calculate the power of the whisk.

The whisk has several settings that allow the beater to spin at different speeds.

A faster beater speed needs a greater power input from the mains electricity supply.

What is the potential difference between the live wire and neutral wire in the mains electricity supply?

Changing the beater speed does not change the potential difference between the live wire and neutral wire.

The power input to the whisk changes because the current in the whisk changes.

Complete the sentence.

When the beater speed increases, the current in the whisk increases because the

Figure 1 shows an electric whisk that plugs into the mains electricity supply.

The whisk can mix food by spinning a beater.

Give two energy stores that increase when the whisk is switched on.

Use the Physics Equations Sheet to answer questions 01.2 and 01.3.

Work is done by the whisk when it is used to mix food.

Write down the equation that links power (P), time (t) and work done (W).

The power output of the whisk is 92 W.

Calculate the time for the whisk to do 23 000 J of work.

Use the Physics Equations Sheet to answer questions 01.4 and 01.5.

Which equation links current (I), power (P) and resistance (R)?

Tick () one box.

The current in the whisk is 500 mA.

The resistance of the whisk is 640 Ω.

Calculate the power of the whisk.

The whisk has several settings that allow the beater to spin at different speeds.

A faster beater speed needs a greater power input from the mains electricity supply.

What is the potential difference between the live wire and neutral wire in the mains electricity supply?

Changing the beater speed does not change the potential difference between the live wire and neutral wire.

The power input to the whisk changes because the current in the whisk changes.

Complete the sentence.

When the beater speed increases, the current in the whisk increases because the

A gardener wanted to build an electrical circuit to monitor the temperature in a greenhouse.

Which symbol represents an electrical component with a resistance that decreases as its temperature increases?

Tick (✓) one box.

When the resistance of an electrical circuit decreases, the current in the circuit increases.

Complete the sentence.

Choose the answer from the box.

Electrical current is a flow of.

The gardener wanted to find how the resistance of the component varies with temperature.

Figure 4 shows the equipment used by the gardener.

The resistance meter displays the resistance of the component.

Plan a method the gardener could use to find how the resistance of the component varies with temperature.

Figure 5 shows how the resistance of the component varies with temperature.

Complete the sentence.

Choose the answer from the box.

The relationship between the temperature and the resistance of the component

is.

The temperature in the greenhouse changed from 10 °C to 30 °C.

Determine the change in resistance of the component between these temperatures.

Use Figure 5.

The gardener builds a circuit that switches a heater on when the greenhouse gets

too cold.

Use the Physics Equations Sheet to answer questions 04.6 and 04.7.

Write down the equation that links current (I), potential difference (V) and power (P).

The power of the heater is 2900 W.

The potential difference across the heater is 230 V.

Calculate the current in the heater.

Figure 7 shows how the National Grid transfers energy from a power station to some street lamps.

Explain how transformer X increases the efficiency of the National Grid.

The potential difference across the primary coil in transformer Y is 400 000 V. The potential difference across the secondary coil is 11 000 V. The current in the primary coil is 660 A. Calculate the current in the secondary coil of transformer Y. Use the Physics Equations Sheet.

Why is the current in each street lamp less than the current in the secondary coil in transformer Y ? Tick (✓) one box.

Figure 8 shows the top of a street lamp.

The light sensor detects if it is day or night. Figure 9 shows part of the circuit in the light sensor.

Explain what happens to the potential difference across resistor R as the light intensity decreases.

When the current in resistor R is 20 mA, the power transferred by resistor R is 6.0 W. Calculate the resistance of resistor R. Use the Physics Equations Sheet.

A student investigated how the potential difference across a filament lamp affects the current in the lamp.

Figure 1 shows the circuit the student used.

Figure 2 shows a circuit symbol.

What component does the symbol represent?

Tick (✓) one box.

Which component from Figure 1 did the student use to adjust the potential difference across the lamp?

When the voltmeter was not connected to the circuit it gave a reading of 0.4 volts.

How can the student correct all the readings taken from the voltmeter?

Tick (✓) one box.

The student recorded three values of current for each potential difference.

Table 1 shows the results for 2.5 volts.

Calculate the mean current in the lamp.

Calculate the power of the lamp when the potential difference across the lamp was 4.8 V

The current in the lamp was 0.75 A

Use the equation:

power = potential difference × current

Calculate the resistance of the lamp when the potential difference across the lamp was 4.8 V

The current in the lamp was 0.75 A

Use the equation:

Complete the sentence.

Choose answers from the box.

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

Increasing the current in a filament lamp makes the temperature

Which graph shows the relationship between potential difference and current for a filament lamp?

Tick (✓) one box.

A student made measurements to determine the specific heat capacity of vegetable oil.

Figure 10 shows the equipment used.

Describe how the student could use the equipment shown in Figure 10 to determine the specific heat capacity of vegetable oil.

Give one risk when using the equipment in Figure 10.

A different student did not have a joulemeter and calculated the energy transferred by the electric heater.

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

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

The electric heater had a power output of 50 watts.

Calculate the time taken for the electric element to transfer 4750 joules of energy to the vegetable oil.

In a deep fryer, vegetable oil is heated by an electric heating element. Food is then cooked in the hot vegetable oil.

The deep fryer contains an electrical component to monitor the temperature of the vegetable oil.

Figure 11 shows how the resistance of this electrical component changes with temperature.

What electrical component is used to monitor the temperature of the vegetable oil?

The electric heating element in the deep fryer automatically switches off when the vegetable oil reaches a certain temperature.

Figure 12 shows how the temperature of the vegetable oil changed after the deep fryer was switched on.

Determine the resistance of the electrical component when the electric heating element automatically switched off.

Use Figure 11 and Figure 12.

Some chips were put in the deep fryer.

In the deep fryer, water in the chips underwent a physical change and became steam.

Why is this a physical change?

Tick (✓) one box.

A student made measurements to determine the specific heat capacity of vegetable oil. Figure 2 shows the equipment used.

Describe how the student could use the equipment shown in Figure 2 to determine the specific heat capacity of vegetable oil.

Give one risk when using the equipment in Figure 2.

A different student did not have a joulemeter and calculated the energy transferred by the electric heater.

Use the Physics Equations Sheet to answer questions 02.3 and 02.4.

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

The electric heater had a power output of 50 watts. Calculate the time taken for the electric element to transfer 4750 joules of energy to the vegetable oil.

In a deep fryer, vegetable oil is heated by an electric heating element. Food is then cooked in the hot vegetable oil. The deep fryer contains an electrical component to monitor the temperature of the vegetable oil. Figure 3 shows how the resistance of this electrical component changes with temperature.

What electrical component is used to monitor the temperature of the vegetable oil?

The electric heating element in the deep fryer automatically switches off when the vegetable oil reaches a certain temperature. Figure 4 shows how the temperature of the vegetable oil changed after the deep fryer was switched on.

Determine the resistance of the electrical component when the electric heating element automatically switched off. Use Figure 3 and Figure 4.

Some chips were put in the deep fryer. In the deep fryer, water in the chips underwent a physical change and became steam. Why is this a physical change? Tick (✓) one box.

The camera in a mobile phone uses an LED to provide light when taking a photograph. A student investigated how the potential difference across an LED varies with the current in it. Figure 9 shows the circuit used.

The student closed the switch. The voltmeter gave a reading of 5.0 V The ammeter gave a reading of 0 mA The LED did not emit any light. Explain how the student should have changed the circuit to make the LED emit light.

The student changed the circuit so that the LED emitted light. The current in the circuit was 290 mA The power of the LED was 0.98 W Calculate the potential difference across the LED. Use the Physics Equations Sheet. Give your answer to 2 significant figures.

A traditional camera uses a flash unit to provide light. Figure 10 shows a flash unit on a traditional camera.

The flash unit emits light from xenon gas in a fluorescent tube. What happens when a xenon atom emits light? Tick (✓) one box.

When the flash unit is used there is a mean potential difference of 200 V across the fluorescent tube. The flash of light lasts for 2.8 × 10^–4 s 1.4 J of energy is transferred. Calculate the mean current. Use the Physics Equations Sheet.

A filament lamp breaks if the electric current in the filament becomes too big.

What is the correct symbol for a filament lamp?

Tick (✓) one box.

What is meant by an electric current?

Tick (✓) one box.

A manufacturer investigated the maximum current value of some filament lamps.

Figure 6 shows the symbols for an ammeter, a battery and a variable resistor.

The manufacturer connected an ammeter, battery, filament lamp and variable resistor in series.

Draw a circuit diagram to show the manufacturer’s circuit.

Include the symbol for a filament lamp from Question 03.1

How could the manufacturer increase the current in the filament lamp?

Tick (✓) one box.

When the potential difference across a filament lamp was 0.75 V, the current in the filament lamp was 0.16 A.

Calculate the power of the filament lamp.

Use the equation:

power = potential difference × current

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

The manufacturer increased the current in the filament lamp to 200 mA.

Calculate the charge flow through the filament lamp in 15 s.

The manufacturer increased the current in the filament lamp from 200 mA.

The filament in the lamp broke when the current reached 320 mA.

How many times greater than 200 mA was the current at which the filament broke?

The manufacturer tested lots of filament lamps.

The current at which the filament lamps broke was 320 ± 60 mA.

What is the range of currents at which the filament lamps broke?

Tick (✓) one box.

Figure 9 shows a mobile phone with its battery removed.

A student measured the potential difference across the battery and then put the battery into the phone.

What is the equation linking current (I), potential difference (V) and resistance (R)?

Tick (✓) one box.

The current in the electronic circuit in the mobile phone was 0.12 A.

The potential difference across the battery was 3.9 V.

Calculate the resistance of the electronic circuit in the mobile phone.

Write down the equation which links energy (E), power (P) and time (t).

The battery was fully charged when it was put into the mobile phone.

The battery discharged when the mobile phone was switched on.

The average power output of the battery as it discharged was 0.46 watts.

The time taken to fully discharge the battery was 2500 minutes.

Calculate the energy transferred by the battery.

The mobile phone includes a sensor to monitor the temperature of the battery.

Figure 10 shows the circuit symbol for a component used in the sensor.

What component does the circuit symbol shown in Figure 10 represent?

The temperature of the component in Figure 10 increases.

The potential difference across the component remains constant.

Explain what happens to the current in the component.

Figure 1 shows a mobile phone with its battery removed.

A student measured the potential difference across the battery and then put the battery into the phone.

What is the equation linking current (I), potential difference (V) and resistance (R)? Tick (✓) one box.

The current in the electronic circuit in the mobile phone was 0.12 A. The potential difference across the battery was 3.9 V. Calculate the resistance of the electronic circuit in the mobile phone.

Write down the equation which links energy (E), power (P) and time (t).

The battery was fully charged when it was put into the mobile phone. The battery discharged when the mobile phone was switched on. The average power output of the battery as it discharged was 0.46 watts. The time taken to fully discharge the battery was 2500 minutes. Calculate the energy transferred by the battery.

The mobile phone includes a sensor to monitor the temperature of the battery.

Figure 2 shows the circuit symbol for a component used in the sensor.

What component does the circuit symbol shown in Figure 2 represent?

The temperature of the component in Figure 2 increases. The potential difference across the component remains constant. Explain what happens to the current in the component.

A TENS machine uses an electrical current to relieve pain. Figure 8 shows the electrodes of a TENS machine connected across an ankle.

The maximum power of the TENS machine is 240 mW. The potential difference across the battery in the TENS machine is 2.5 V. Calculate the maximum current from the battery.

Figure 9 is a sketch graph showing how the potential difference across the electrodes varies with time.

A student concluded that there was an alternating potential difference across the electrodes. How does Figure 9 show that the student was not correct?

Figure 10 shows a circuit the student built using the battery from the TENS machine.

The student recorded how the current in the resistor varied with the potential difference across the resistor. Figure 11 shows a sketch graph of the results.

What relationship does Figure 11 show?

Figure 12 shows two more circuits that the student built using the battery from the TENS machine.

The resistors all have the same resistance. Compare the readings on the voltmeter and ammeter in circuit A and circuit B.

A student investigated how the resistance of a wire varies with the length of the wire. Figure 1 shows the circuit used.

The symbols for the voltmeter and ammeter in Figure 1 are not complete. Complete the symbols for the voltmeter and ammeter in Figure 1.

Which variable is the independent variable? Tick (✓) one box.

Which variable is the dependent variable? Tick (✓) one box.

The student took repeat readings of potential difference for a 30 cm length of the wire. The readings were: 0.16 V 0.17 V 0.15 V

Calculate the mean potential difference.

The length of the wire was increased to 60 cm The current in the wire was 0.50 A The mean potential difference across the wire was 0.32 V

Calculate the resistance of the 60 cm length of wire. Use the equation:

Calculate the power dissipated in the 60 cm length of wire. Use the equation: power = potential difference × current

Calculate the charge flow when there is a current of 0.50 A in the wire for 17 s Use the equation: charge flow = current × time

Figure 2 is a sketch graph of the results.

The student repeated the investigation using a thicker wire made from the same metal. For the same length, the thicker wire has a lower resistance. Draw a line on Figure 2 to show how the resistance of the thicker wire varies

A designer made some shoes that have lights in them.

Each shoe has a switch which closes when a person puts their foot on the floor.

Figure 1 shows the circuit.

What is component X ?

Tick (✓) one box.

Complete the sentence.

Choose the answer from the box.

When the switch was closed, the current in component X was

the current in the resistor.

The designer tested how the number of cells affected the number of steps that could be taken before the lights stopped working.

Figure 2 shows the results.

Determine how many more steps could be taken when the number of cells was increased from 3 to 5

How could the designer check the repeatability of the results?

Tick (✓) one box.

When the potential difference across the resistor was 0.80 V, the current in the resistor was 0.020 A

Calculate the power dissipated by the resistor.

Use the equation: power = potential difference × current

Which other equation can be used to calculate the power dissipated by a resistor?

Tick (✓) one box.

What happens to the temperature of the resistor when there is a current in it?

There was a current of 0.020 A in the resistor for 180 seconds.

Calculate the charge flow through the resistor.

Use the equation:

charge flow = current × time

A student investigated how the area of a solar panel affected the output potential difference of the solar panel.

The student placed different sized solar panels under a lamp.

Figure 3 shows a solar panel under a lamp.

Which variable should be controlled?

Tick (✓) one box.

The student measured the output potential difference using a voltmeter.

When the voltmeter was not connected, the reading on the voltmeter was 0.7 V

What name is given to this type of error?

Tick (✓) one box.

Table 1 shows the results of the investigation.

The readings for which solar panel show an anomalous result?

Tick (✓) one box.

The student did not have a solar panel with an area of 40 cm²

Determine the most likely value for the mean output potential difference of a 40 cm² solar cell.

The total input energy transfer to one of the solar panels was 8.0 joules.

The useful output energy transfer was 0.96 joules.

Calculate the efficiency of the solar panel.

Use the equation:

Solar power is a renewable energy resource.

Complete the sentence.

Choose the answer from the box.

Some homes have solar panels which generate electricity.

On a sunny day the potential difference across a solar panel is 31 volts.

A charge of 490 coulombs flows through the solar panel.

Calculate the energy transferred by the solar panel.

Use the equation:

energy transferred = charge flow × potential difference

Give your answer to 2 significant figures.

Why do solar panels on homes help reduce the environmental impact of using electrical devices?

Tick (✓) one box.

Figure 7 shows a toaster.

The toaster is connected to the mains supply using a three-core cable.

What is the function of the earth wire inside the cable?

Tick (✓) one box.

Complete the sentences.

Choose answers from the box.

The toaster is switched on for 120 seconds.

The power of the toaster is 850 watts.

Calculate the energy transferred by the toaster.

Use the equation:

energy transferred = power × time

Complete the sentences.

Choose answers from the box.

When bread is lowered into the toaster, a spring is stretched. The stretched spring

After the bread is toasted, the spring makes the toast move upwards. As the

the toast increases.

Write the equation which links gravitational field strength, gravitational potential energy, height and mass.

The toast was moved upwards by the spring.

The change in gravitational potential energy of the toast was 0.049 J

The mass of the toast was 0.050 kg

gravitational field strength = 9.8 N/kg

Calculate the change in height of the toast.

A hybrid car has an electric motor and a petrol engine.

Petrol is a non-renewable energy resource. What is meant by a non-renewable energy resource?

The electric motor in the car is powered by a battery. To charge the battery, the car is plugged into the mains supply at 230 V The power used to charge the battery is 6.9 kW Calculate the current used to charge the battery.

Mains electricity is an ac supply. Explain the difference between direct and alternating potential difference.

The cable used to connect the car to the mains electricity supply has a low resistance. Explain why it is better to use a cable with a low resistance than to use a cable with a high resistance.

A student investigated how the mass of water in an electric kettle affected the time taken for the water to reach boiling point. The kettle switched off when the water reached boiling point. Figure 4 shows the kettle.

The heating element of the kettle was connected to the mains supply. Explain why the temperature of the heating element increased.

Give one variable that the student should have controlled.

Figure 5 shows how the mass of water in the kettle affected the time taken for the kettle to switch off.

Suggest why the line on Figure 5 does not go through the origin.

Suggest why the results give a non-linear pattern.

The power of the kettle was 2.6 kW The kettle took 120 seconds to heat 0.80 kg of water from 18 °C to 100 °C Calculate the specific heat capacity of water using this information. Give your answer to 2 significant figures.

Figure 3 shows a mobile phone being recharged by a portable power source.

Why does the battery in the phone need recharging?

Tick one box.

The power source provides a current of 1.86 A at a potential difference of 3.90 V

Calculate the power of the power source.

Use the equation:

power = potential difference × current

Choose the correct unit from the box.

A student needs a new power source.

Figure 4 shows three different sized power sources.

Table 1 gives data about the different power sources.

The student chose the large power source.

Suggest why the student chose the large power source.

A student built a circuit using filament lamps.

Sketch a current potential difference graph for a filament lamp on Figure 9

Figure 10 shows the circuit with two identical filament lamps.

Compare the currents I₁, I₂ and I₃

Calculate the charge that flows through the cell in 1 minute. Each filament lamp has a power of 3 W and a resistance of 12 Ω Write any equations that you use. Give the unit.

The student builds a different circuit. Figure 11 shows the circuit.

Explain how the readings on both meters change when the environmental conditions change.