Resistors & I-V characteristics

A student investigated how the current in an LED varies with the potential difference across the LED.

Figure 18 shows the circuit used.

Figure 19 shows the results.

Give one way the student could have varied the potential difference across the LED.

Use the Physics Equations Sheet to answer questions 10.2 and 10.3.

Which of the following equations links current (I), potential difference (V) and resistance (R)?

Tick () one box.

Determine the resistance of the LED when the potential difference across the LED was 3.0 V.

Use Figure 19.

The student reversed the connections to the power supply and varied the potential difference across the LED.

Explain why the ammeter displayed a value of 0.0 A for all the values of potential difference the student used.

A student investigated how the current in an LED varies with the potential difference across the LED.

Figure 5 shows the circuit used.

Figure 6 shows the results.

Give one way the student could have varied the potential difference across the LED.

Use the Physics Equations Sheet to answer questions 03.2 and 03.3.

Which of the following equations links current (I), potential difference (V) and resistance (R)?

Tick () one box.

Determine the resistance of the LED when the potential difference across the LED was 3.0 V.

Use Figure 6.

The student reversed the connections to the power supply and varied the potential difference across the LED.

Explain why the ammeter displayed a value of 0.0 A for all the values of potential difference the student used.

Figure 4 shows a student putting a coin into a vending machine that sells food.

The vending machine is connected to the mains electricity supply.

What is the frequency of the mains electricity supply in the UK?

Tick () one box.

What is the potential difference of the mains electricity supply in the UK?

Tick () one box.

The vending machine identifies the value of the coin by measuring the resistance of the coin.

The machine applies a potential difference of 0.45 V across the coin.

The current in the coin is 0.75 A.

Calculate the resistance of the coin.

Use the equation:

The temperature inside the vending machine is monitored using an electrical circuit.

Figure 5 shows part of the circuit.

The circuit symbol for the thermistor is wrong.

What is the circuit symbol for a thermistor?

Tick () one box.

How could the potential difference (pd) across the resistor be calculated?

Tick () one box.

At one temperature, the thermistor in Figure 5 has a resistance of 200 Ω.

What is the potential difference across the thermistor at this temperature?

Give a reason for your answer.

Tick () one box.

Figure 6 shows how the resistance of the thermistor varies with temperature.

When the temperature of the thermistor is 10 °C, the resistance of the thermistor is 600 Ω.

Calculate the change in resistance when the temperature increased from 10 °C to 15 °C.

A student had an unknown electrical component inside a sealed box.

Figure 14 shows the circuit the student used to identify the component.

The student varied the potential difference across the component and measured the current in the component.

Table 3 shows the results when the potential difference across the component was 6.0 V.

Calculate value X in Table 3.

Figure 15 shows the results.

Calculate the power of the component when the potential difference across the component is 3.0 V.

Use Figure 15 and the equation:

power = potential difference × current

Complete the sentence.

Choose the answer from the box.

As the potential difference across the component increases, the gradient of

What is the component in the sealed box?

Tick () one box.

A student investigated how the length of a wire affects the resistance of the wire at constant temperature.

Figure 3 shows the circuit used.

The student plotted a graph of resistance against the length of wire.

Describe a method the student could have used to collect the data needed to plot the graph.

Which graph shows the relationship between the resistance of a wire at constant temperature and its length?

Tick (✓) one box.

The student used a cell that had a potential difference of 1.50 V.

Explain why the cell was not an electrical hazard to the student in the investigation.

Figure 7 shows a student putting a coin into a vending machine that sells food.

The vending machine is connected to the mains electricity supply.

What is the frequency and the potential difference of the mains electricity supply in the UK?

The vending machine identifies the value of the coin by measuring the resistance of the coin.

The power dissipated by the coin is 340 mW when the current in the coin is 0.75 A.

Calculate the resistance of the coin.

Use the Physics Equations Sheet.

Coins that are dirty are not recognised by the vending machine.

Suggest one reason why.

Figure 8 shows part of a different circuit that is used to monitor the temperature inside

the vending machine.

The circuit symbol for a thermistor has not been included.

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

Figure 9 shows how the resistance of the thermistor varies with temperature.

The cooling system inside the vending machine turns on when the temperature of the thermistor is above 20 °C.

Determine the potential difference across the thermistor when the temperature is 20 °C.

Use the Physics Equations Sheet.

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

Figure 1 shows the circuit used.

What is component P ?

Complete the sentences.

Choose answers from the box.

The ammeter in the circuit measures.

The voltmeter in the circuit measures.

How will increasing the resistance of the variable resistor in Figure 1 affect each of the following quantities?

Tick (✓) one box in each row.

A charge flow of 15 coulombs passed through the filament lamp in a time of 60 seconds.

Calculate the current in the lamp.

Use the equation:

When the current in the filament lamp is 0.12 A, the potential difference across the lamp is 6.0 V.

Calculate the resistance of the filament lamp.

Use the equation:

The student repeated the investigation after replacing the lamp with a resistor at constant temperature and then a diode.

The student plotted a graph for each component.

Draw one line from each component to its graph.

Figure 2 shows an ammeter.

The ammeter is not connected to a circuit.

What type of error does the ammeter display?

Tick (✓) one box.

A student investigated how the current in a filament lamp varies with the potential difference across the filament lamp. Figure 6 shows the results.

Describe a method the student could use to obtain these results. You should include a circuit diagram.

Determine the resistance of the filament lamp when the potential difference across it is +3.0 V. Use the Physics Equations Sheet. Use Figure 6 on page 18.

The current in the lamp is 0.21 A when the potential difference across the lamp is 6.0 V. Calculate the energy transferred by the filament lamp in 30 minutes. Use the Physics Equations Sheet.

The power output of the lamp is 1.0 W when the potential difference across the lamp is 5.0 V. A student predicts that the power output would be 4.0 W if the potential difference was doubled. Explain why the student is not correct.

Student A investigated how the current in resistor R at constant temperature varied with the potential difference across the resistor.

Student A recorded both positive and negative values of current.

Figure 14 shows the circuit Student A used.

Describe a method that Student A could use for this investigation.

Student B repeated the investigation.

During Student B ’s investigation the temperature of resistor R increased.

Explain how the increased temperature of resistor R would have affected Student B ’s results.

Figure 15 shows the scale on a moving coil ammeter at one time in the investigation.

What is the resolution of the moving coil ammeter?

Student B replaced the moving coil ammeter with a digital ammeter.

Figure 16 shows the reading on the digital ammeter.

The digital ammeter has a higher resolution than the moving coil ammeter.

Give one other reason why it would have been better to use the digital ammeter throughout this investigation.

Student A investigated how the current in resistor R at constant temperature varied with the potential difference across the resistor. Student A recorded both positive and negative values of current. Figure 2 shows the circuit Student A used.

Describe a method that Student A could use for this investigation.

Student B repeated the investigation. During Student B ’s investigation the temperature of resistor R increased. Explain how the increased temperature of resistor R would have affected Student B ’s results.

Figure 3 shows the scale on a moving coil ammeter at one time in the investigation.

What is the resolution of the moving coil ammeter?

Student B replaced the moving coil ammeter with a digital ammeter. Figure 4 shows the reading on the digital ammeter.

The digital ammeter has a higher resolution than the moving coil ammeter. Give one other reason why it would have been better to use the digital ammeter throughout this investigation.

A student heated water in an electric kettle.

Water has a high specific heat capacity. Complete the sentence. Choose answers from the box.

The specific heat capacity of a substance is the energy needed to raise the

The kettle circuit contains a thermistor which is used to switch the kettle off when the water reaches 100 °C. What is the correct symbol for a thermistor? Tick (✓) one box.

The resistance of the heating element in the kettle is 15 Ω. The current in the heating element is 12 A. Calculate the power of the heating element. Use the equation: power = (current)² resistance

The student investigated how quickly the kettle could increase the temperature of 0.50 kg of water. Figure 10 shows the results of the investigation.

The temperature of the water did not start to increase until 10 seconds after the kettle was switched on. What is the reason for this? Tick (✓) one box.

Describe a method the student could have used to obtain the results shown in Figure 10.

The mass of water in the kettle was 0.50 kg. The temperature of the water increased from 20 °C to 100 °C. specific heat capacity of water = 4200 J/kg °C Calculate the energy transferred to the water. Use the Physics Equations Sheet.

The water in the kettle boiled for a short time before the kettle switched off. During this time 5.0 g of water changed to steam. specific latent heat of vaporisation of water = 2 260 000 J/kg Calculate the energy transferred to change the water to steam. Use the Physics Equations Sheet.

A student investigated how the current in a filament lamp varied with the potential difference across the filament lamp. Figure 11 shows part of the circuit used.

Figure 11

Complete Figure 11 by adding an ammeter and a voltmeter. Use the correct circuit symbols.

Figure 12 shows some of the results.

The student reversed the connections to the power supply and obtained negative values for the current and potential difference. Draw a line on Figure 12 to show the relationship between the negative values of current and potential difference.

Write down the equation which links current (I), potential difference (V) and resistance (R).

Determine the resistance of the filament lamp when the potential difference across it is 1.0 V. Use data from Figure 12.

A second student did the same investigation. The ammeter used had a zero error. What is meant by a zero error?

A student investigated how the current in a filament lamp varied with the potential difference across the filament lamp. Figure 1 shows part of the circuit used.

Figure 1

Complete Figure 1 by adding an ammeter and a voltmeter. Use the correct circuit symbols.

Figure 2 shows some of the results.

The student reversed the connections to the power supply and obtained negative values for the current and potential difference. Draw a line on Figure 2 to show the relationship between the negative values of current and potential difference.

Write down the equation which links current (I), potential difference (V) and resistance (R).

Determine the resistance of the filament lamp when the potential difference across it is 1.0 V. Use data from Figure 2.

A second student did the same investigation. The ammeter used had a zero error. What is meant by a zero error?

Figure 6 shows how much electricity was generated using coal-fired and gas-fired power stations in January for 5 years in the UK.

Determine the percentage increase in electricity generated using gas-fired power stations from 2014 to 2018.

Give two environmental advantages of using a gas-fired power station to generate electricity compared with using a coal-fired power station.

The mean surface temperature of the sea changes throughout the year.

A change in the mean surface temperature from year to year indicates climate change. Figure 7 shows how the mean surface temperature changed between 1988 and 2016.

A student does not believe that climate change is occurring. Explain how the data in Figure 7 suggests the student is wrong.

A thermistor can be used to measure temperature. Figure 8 shows how the resistance of four different thermistors A, B, C and D, varies with temperature.

Which of the four thermistors would be the most suitable to measure the surface temperature of the sea? Tick (✓) one box. Explain your answer.

Figure 2 shows how the current through a filament lamp changes after the lamp is switched on.

The normal current through the filament lamp is 1.5 A.

For how many seconds is the current through the filament lamp greater than 1.5 A?

Tick one box.

Why might the filament inside a lamp melt when the lamp is first switched on?

The lamp is connected to a 24 V power supply. The current through the lamp is 1.5 A.

Calculate the power of the lamp.

Use the equation: power = potential difference × current

LED lamps are much more efficient than filament lamps.

What does this statement mean?

Tick one box.

A student investigated how the resistance of a piece of nichrome wire varies with length.

Figure 17 shows part of the circuit the student used.

Figure 17

Complete Figure 17 by adding an ammeter and a voltmeter.

Use the correct circuit symbols.

Describe how the student would obtain the data needed for the investigation.

Your answer should include a risk assessment for one hazard in the investigation.

Why would switching off the circuit between readings have improved the accuracy of the student’s investigation?

Tick one box.

A student investigated how the resistance of a piece of nichrome wire varies with length.

Figure 3 shows part of the circuit that the student used.

Complete Figure 3 by adding an ammeter and a voltmeter.

Use the correct circuit symbols.

Describe how the student would obtain the data needed for the investigation.

Your answer should include a risk assessment for one hazard in the investigation.

Why would switching off the circuit between readings have improved the accuracy of the student’s investigation?

Tick one box.

Complete the sentence. Choose answers from the box.

The current through an ohmic conductor is directly proportional to the

that the
remains constant.

Figure 7 shows a current – potential difference graph for a filament lamp.

Explain how the resistance of a filament lamp changes as the potential difference across it increases.

Many householders are replacing their filament lamps with LED lamps which are more energy efficient.

What does more energy efficient mean?

A Light Dependent Resistor (LDR) is used to turn on an outside lamp when it gets dark.

Part of the circuit is shown in Figure 8.

The light intensity decreases.

What happens to the potential difference across the LDR and the current in the LDR?

Potential difference

What is the resistance of the LDR when the potential difference across it is 4 V?

Give a reason for your answer.

Calculate the current through the LDR when the resistance of the LDR is 5000 Ω.

Give your answer to 2 significant figures.