Resistors and I-V characteristics

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.

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 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.

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

Figure 6 shows an incomplete diagram of the circuit used.

The student measured the potential difference across the diode.

Complete Figure 6 by adding the symbol for a voltmeter in the correct position.

Which component should the student adjust to change the potential difference across the diode?

Tick (✓) one box.

The student measured the current three times for each value of potential difference.

Complete the sentence.

Choose the answer from the box.

When the potential difference was 1.50 V the current measurements varied between

Figure 7 shows some of the results.

Table 2 shows the results when the potential difference was greater than 1.00 V.

Complete Figure 7.

You should:

• plot the results from Table 2

• draw a line of best fit.

Complete the sentence.

Choose the answer from the box.

Figure 7 shows that the relationship between potential difference and current for the

diode is.

The student adjusted the circuit so that the current in the diode was 1.00 A.

The student then reversed the connections to the diode.

What happened to the current in the diode when the connections were reversed?

Tick (✓) one box.

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

Figure 3 shows an incomplete diagram of the circuit used.

Complete Figure 3 to show how the student should have connected a voltmeter and an ammeter into the circuit.

Use the correct circuit symbols.

The potential difference across the battery was +2.6 V.

The student varied the potential difference across the LED between –2.6 V and +2.6 V.

Describe how the student should have adjusted the circuit to vary the potential difference across this range.

Table 1 shows the results when the potential difference across the LED had positive values.

Figure 4 shows a graph of current against potential difference.

Complete Figure 4.

You should:

• plot the remaining points from Table 1

• draw a line of best fit.

Explain what happens to the current in the LED when the potential difference across the LED is negative.

A second student did the investigation using a blue LED.

The results for both the red LED and the blue LED showed the same pattern.

What conclusion can be made about the investigation?

Tick () one box.

The relationship between current and potential difference for an LED is non-linear.

Which of the following always shows a linear relationship between current and potential difference?

Tick () one box.

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.

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 piece of wire varies with its length.

Figure 2 shows the circuit used.

Explain why the student needed to adjust the variable resistor each time she changed the length of the wire.

The student recorded three measurements of the potential difference across a 0.10 m length of wire. Table 1 shows the results.

Calculate X in Table 1.

Figure 3 shows the results for five different lengths of the wire.

Describe the relationship between the length of the wire and the resistance of the wire.

A glucometer uses the resistance of a blood sample to calculate the glucose concentration in a person’s blood. A blood sample is put into a small tube, which is put inside the glucometer. The blood then acts like a resistance wire. Figure 4 shows the relationship between the resistance of a blood sample and the glucose concentration.

The glucometer applies a potential difference of 0.90 volts across a blood sample. The glucose concentration of the blood sample is 0.98 grams/litre. Determine the current in the blood sample.

A new tube is used each time a blood sample is tested. Explain why valid results are only obtained if each tube is identical.

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

Figure 8 shows part of the circuit used.

The student connected an ammeter and a voltmeter into the circuit.

What is the correct way to connect the ammeter and the voltmeter into the circuit?

The student increased the resistance of the variable resistor.

How did increasing the resistance affect the current in the circuit?

How should the student change the circuit to give negative values for current and potential difference?

Name the type of relationship between current and potential difference for a resistor at constant temperature.

Write the equation which links current, potential difference and resistance.

The current in the resistor was 0.12 A when the potential difference across the resistor was 3.0 V

Calculate the resistance of the resistor.

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

The student connected an ammeter and a voltmeter into the circuit. What is the correct way to connect the ammeter and the voltmeter into the circuit?

The student increased the resistance of the variable resistor. How did increasing the resistance affect the current in the circuit?

How should the student change the circuit to give negative values for current and potential difference?

Name the type of relationship between current and potential difference for a resistor at constant temperature.

Write the equation which links current, potential difference and resistance.

The current in the resistor was 0.12 A when the potential difference across the resistor was 3.0 V Calculate the resistance of the resistor.

Figure 2 shows a circuit that a student built.

The lamp has a resistance of 10 Ω Each resistor has a resistance of 10 Ω What is the total resistance of the circuit?

Tick (✓) one box.

Explain your answer to Question 04.1

The student replaced one of the resistors with a thermistor.

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

The student increased the temperature of the thermistor. Explain how the current in the thermistor changed.

Figure 3 shows another circuit the student built.

Explain how the potential difference across the resistor and the lamp will change when the switch is closed.

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.