OCR GCSE Combined Science
A 40 V power supply transfers 10 C of charge.
What is the energy transferred?
Use the equation: energy transferred = charge × potential difference
A 0.25 J
B 4.00 J
C 400 J
D 4000 J
The diagram shows a power station connected to a town by the national grid.
Power Station Transformer Pylons and Wires Transformer
Town
The national grid uses alternating voltage.
A simple circuit powered by a battery uses direct voltage.
Explain the difference between alternating voltage and direct voltage.
The table shows the current in one of the wires in the national grid at two different voltages.
| Voltage across wire (V) | Current in wire (A) |
| 11 000 | 730 |
| 400 000 | 20 |
The wire has a resistance of 2.0 
.
Calculate how much power is dissipated from the wire at 11 000 V.
Use the equation: power = current2 
resistance
Give your answer to 2 significant figures and in MW.
The national grid transfers 8 000 kJ of energy from the power station every second.
When the voltage across the wires is 400 000 V, the transformers and wires dissipate 160 kJ of this energy every second.
Calculate the efficiency of the energy transfer at 400 000 V.
Explain how step-up transformers allow the national grid to transfer energy more efficiently.
A UK mains plug has 3 wires: live, neutral and earth.
Describe the function of the neutral wire.
A 2 V power supply is connected to a motor. 250 C passes in 50 s.
How much energy is transferred?
Use the equation: energy transferred = charge × potential difference
A 5 J
B 100 J
C 125 J
D 500 J
The national grid uses alternating voltage.
A simple circuit powered by a battery uses direct voltage.
Explain the difference between alternating voltage and direct voltage.
The table shows the current in one of the wires in the national grid at two different voltages.
| Voltage across wire (V) | Current in wire (A) |
| 11 000 | 730 |
| 400 000 | 20 |
The wire has a resistance of 2.0 .
Calculate how much power is dissipated from the wire at 11 000 V.
Use the equation: power = current2 
resistance
Give your answer to 2 significant figures and in MW.
The national grid transfers 8 000 kJ of energy from the power station every second.
When the voltage across the wires is 400 000 V, the transformers and wires dissipate 160 kJ of this energy every second.
Calculate the efficiency of the energy transfer at 400 000 V.
Explain how step-up transformers allow the national grid to transfer energy more efficiently.
A UK mains plug has 3 wires: live, neutral and earth.
Describe the function of the neutral wire.
This is a diagram of a transformer.
Calculate the power output from the secondary coil.
Use the equation: power = potential difference 
current
Name the type of transformer shown in the diagram.
Where can this type of transformer be used in the national grid?
Tick (✓) one box.
The energy input to the primary coil is 200 kJ.
The energy output from the secondary coil is 180 kJ.
Calculate the efficiency of the transformer.
This question is about transformers.
Complete the sentences to describe how transformers are used in the national grid.
A step‑up / step‑down transformer increases current / potential difference at the power station.
A step‑up / step‑down transformer increases / decreases potential difference locally for domestic use.
A student researches three different transformers A, B and C.
Transformer A is used to decrease a potential difference from 240 V to 20 V.
The current in the primary coil is 0.8 A.
Calculate the current in the secondary coil.
Use the Equation Sheet.
Transformer B is used in a lighting circuit.
The energy input to the primary coil is 175 J.
The energy output from the secondary coil is 140 J.
Calculate the efficiency of the transformer.
Use the Equation Sheet.
A lamp is connected to the secondary coil of transformer C.
The current in the lamp is 0.25 A. The resistance of the lamp is 800 
.
The lamp is at its normal brightness.
Calculate the output power of transformer C.
Use the Equation Sheet.
A transformer has an output potential difference of 24 V.
The output current is 5 A.
What is the power output of the transformer?
Use the Equation Sheet.
A 0.21 W
B 4.8 W
C 120 W
D 240 W
A student builds the circuit shown in the diagram. W, X, Y and Z are points in the circuit.
Calculate the potential difference between Y and Z.
Use the Equation Sheet.
The resistance of the circuit between Y and Z must be less than 10 .
Explain why.
Calculate the current at W.
Which statement describes the values of the current at W and X ?
Tick (✓) one box.
Calculate the power dissipated by one of the 10 
resistors.
Use the Equation Sheet.
A 6 V battery provides a current of 0.4 A in a circuit for 20 seconds.
How much energy is transferred by the battery?
Use the equations: charge flow = current × time
energy transferred = charge × potential difference
A 0.12 J
B 0.75 J
C 15 J
D 48 J
A 1.5 V cell transfers 18 mC of charge in a circuit.
What is the amount of energy transferred by the cell? Use the Data Sheet.
A 0.027 mJ
B 0.27 J
C 27 mJ
D 27 J
A filament lamp has a resistance of 1000 
and a current of 0.25 A.
What is the power of the filament lamp?
Use the equation: power = (current)2 × resistance
A 62.5 W
B 250 W
C 4000 W
D 250 000 W
A battery in a circuit has a potential difference of 6 V.
How much energy is transferred when 4 C of charge flows?
A 0.4 J
B 0.67 J
C 1.5 J
D 24 J
A 6 V battery transfers 1860 J of energy.
Calculate the charge transferred by the battery.
Use the equation: energy transferred = charge × potential difference
A 0.31 C
B 11.16 C
C 310 C
D 11 160 C
A student wants to check the electrical power of a mains filament lamp.
He sets up the circuit in Fig. 11.1.
Complete the table to describe how he sets up the equipment in Fig. 11.1.
| What is being measured? | Name of meter | Connected in |
| Potential difference | Meter 2 = ………………………. | Parallel |
| ………………………. | Meter 1 = Ammeter | ………………………. |
The student reads the meters in the circuit in Fig. 11.1.
• The value of the potential difference is 230 V.
• The value on the ammeter is 0.5 A.
Calculate the actual power of the mains filament lamp.
Use the equation: power = potential difference × current
Another lamp has a power of 100 W. 1 kW = 1000 W
What is the power of the lamp in kilowatts (kW)?
0.1 kW 1 kW 100 kW 100 000 kW
Suggest how the student can make his readings more precise.
Fig. 11.2 shows a night-light. It contains a 1.0 W lamp and a 3.0 V battery.
The student compares the mains filament lamp with the night-light. They are both used for the same amount of time.
Fig. 11.2
Use these words to complete the sentences.
You can use each word once, more than once, or not at all.
more than less than equal to
The energy transferred by the night-light is …………………………… the energy transferred by the mains filament lamp.
The power of the night-light is …………………………… the power of the mains filament lamp.
This question is about the way electricity is used in the home.
The national grid transfers electrical power from power stations.
The table shows information for different types of power line.
| Power line 1 | Power line 2 | Power line 3 | |
| Voltage (V) | 400 000 | 200 000 | 100 000 |
| Current (A) | 125 | 250 | |
| Power loss (W) | 46 875 | 187 500 | 750 000 |
The resistance of each power line is 3 
.
Calculate the current in power line 3.
Use the equation: power = current2 × resistance
Explain how power loss is reduced in the national grid.
Use the values for power line 1 and power line 2 to help you.
In Fig. 14.1, an electrician wires an electrical socket next to a sink.
The switch on the socket is open. Explain why this situation is dangerous if water enters the socket.
Write about the live wire and earth wire in your answer.
This question is about electrical devices.
The diagram shows two different electrical devices.
Write down the source of electrical energy for each device.
torch........
Describe how energy is dissipated in the electric fan.
The electric fan is rated 230 V, 0.3 A.
Calculate the power of the electric fan.
Use the equation: power = potential difference × current
*(b) Here is a diagram of a tumble dryer and an electric drill. Each appliance is wired differently.
Explain whether the tumble dryer and electric drill are both safe to use.
Include the function of the earth, live and neutral wires in your answer.
An electron is accelerated through a potential difference of 12 000 V. The charge on an electron is 1.60 × 10–19 C.
Calculate the energy transferred to the electron.
Use the equation: energy transferred = charge × potential difference
A 1.33 × 10–23 J
B 1.92 × 10–15 J
C 1.20 × 104 J
D 7.50 × 1022 J
A scientist does an experiment to measure the energy transferred to water.
She uses an immersion heater to increase the temperature of the water.
The scientist uses this apparatus:
• A beaker
• An immersion heater
• A stirring rod
• A 12 V battery and wires.
What two other pieces of apparatus does the scientist need for this experiment?
Explain how the scientist could reduce energy transfer to the surroundings.
The immersion heater is placed at the bottom of the beaker.
Suggest why.
The heater is connected to a battery. When the heater is turned on, energy is transferred.
Describe this energy transfer.
Use ideas about energy stores.
The current through the heater is 3.8 A. The potential difference across the heater is 9.0 V.
Use the equation: Power = Potential difference × Current
Calculate the power of the immersion heater.
The scientist writes down more information about her experiment.
• Mass of water = 150 g
• Specific heat capacity of water = 4200 J / kg °C
• Temperature increase of water = 10 °C
Calculate the change in thermal energy of the water.
Two students investigate how the resistance of a thermistor varies with temperature.
The students place the thermistor in a beaker of water and measure the resistance of the thermistor for 5 different temperatures. They repeat the experiment three times at each temperature in order to calculate a mean.
| Temperature | Resistance ( |  ) | ||
| (°C) | 1 | 2 | 3 | Mean |
| 10 | 1900 | 1870 | 1930 | 1900 |
| 15 | 980 | 1000 | 990 | 990 |
| 20 | 770 | 760 | 760 | 763.3 |
| 25 | 610 | 720 | 610 | 647 |
| 30 | 540 | 540 | 530 | 536 |
Describe the pattern shown by these results.
The students have made mistakes when recording their results.
Identify two mistakes and explain what they should have done.
Suggest one way the experiment could be improved.
At 10 °C the thermistor had a resistance of 1900 
. The thermistor has a power rating of 75 × 10–3 W.
Calculate the maximum current in this thermistor at 10 °C.
Use the equation: Power = Current2 × Resistance
The table shows some information about electrical appliances in the home.
| Appliance | Power (W) | Current (A) | Resistance ( ) |
| Electric drill | 800 | 3.48 | 66.1 |
| Iron | 2000 | 8.69 | 26.5 |
| Kettle | 2500 | 10.86 | 21.1 |
| Security light | 500 | 2.17 | 105.8 |
| Toaster | 1650 | 7.17 | 32.1 |
Use the table to describe the relationship between power and resistance.
Explain this relationship. Use ideas about resistance in your answer.
The security light is switched on for 45 minutes every day for 7 days.
Use the equation: Energy transferred = Power × Time
Calculate the energy transferred in kWh.
Give your answer to 2 significant figures.
Explain the difference between direct voltage and alternating voltage.
The electric drill does not need an earth wire.
Explain why.
Mains electricity can be produced in a power station that burns coal.
An electric iron is plugged into the mains and switched on. The temperature of the iron increases.
Describe this process.
Use ideas about energy stores in your answer.
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