Resistors and I-V characteristics

A thermistor has a resistance which changes with temperature.

Which symbol is a thermistor?

Tick (✓) one box.

A student determines the resistance of a thermistor using an ammeter and a voltmeter.

Complete the diagram to show a circuit they can use.

Diagram

The student finds the resistance of the thermistor at several different temperatures.

The graph shows their results.

Describe the trend between temperature and resistance. Include data from the graph to support your answer.

A thermistor is to be used in the range 20 °C to 40 °C.

Its resistance must change by at least 10 k over this range.

Explain why this thermistor is not suitable? Include data from the graph.

What component changes resistance when there is a change in light level ?

Student A is investigating the question:

‘How does the potential difference across a diode affect the current through it?’

They set up this circuit.

One component is missing from the circuit.

State the name of this component.

Which position should this component be added?

Tick (✓) one box.

A variable resistor is placed next to the battery.

Why is it used in this investigation?

Which potential difference shows an anomalous result?

Tick (✓) one box.

Use the graph to find the current when the potential difference is 2.75 V.

State the maximum potential difference before the diode conducts.

Use the graph.

This question is about how electrical circuits work.

A student builds three different electrical circuits.

Explain why the lamp does not light in each circuit.

Fig. 12.1 shows the first circuit.

Fig. 12.1

The lamp does not light because........

Fig. 12.2 shows the second circuit.

Fig. 12.2

The lamp does not light because........

Fig. 12.3 shows the third circuit.

Fig. 12.3

The lamp does not light because........

The student uses the meters in the circuit in Fig. 12.4 to determine the resistance of a resistor.

Fig. 12.4

The student uses the circuit to take several readings of current and potential difference. The graph shows the student’s results.

Complete the sentence about the graph to explain the relationship between potential difference and current. Use words from the list.

decreases increases stays the same

As the potential difference increases, the current........

The ratio of potential difference: current at 3 V is 15: 1.

Calculate the ratio of potential difference: current at 6 V. Use the graph.

Complete the sentence about the graph. Use a word from the list.

elastic linear non-linear plastic

The graph of current against potential difference for the resistor is........

This diagram shows a cell connected in series with a resistor.

Calculate the potential difference of the cell in the diagram.

Use the equation: potential difference = current × resistance

A student uses the circuit shown in the diagram to measure the resistance of a resistor. M1 and M2 are meters.

Explain the purpose of the variable resistor in the diagram.

Explain why meter M1 in the diagram must be an ammeter.

When meter M1 in the diagram is replaced by a voltmeter, no current flows.

Suggest why.

The graph shows the student’s results from using the circuit.

Calculate the resistance of the resistor. Use the graph.

Complete the sentence about the graph to explain the relationship between potential difference and resistance.

Use words from the list.

decreases increases stays the same

As the potential difference increases, the resistance........

Draw lines to connect each circuit component with its correct symbol.

Circuit component
Symbol

The potential difference across a 3 resistor is 4.5 V.

Calculate the current in the resistor.

Use the Equation Sheet.

A teacher connects the circuit in Fig. 11.2. Fig. 11.2

Both lamps are lit. The teacher then removes lamp A from its holder but leaves the rest of the circuit unchanged.

Describe what happens. Give a reason for your answer.

The teacher connects the circuit in Fig. 11.3. Fig. 11.3

Both lamps are lit. The teacher then removes lamp A.

Describe what happens. Give a reason for your answer.

The graph shows how the current in a resistor changes when the potential difference across the resistor changes.

Which two statements about the graph are correct?

Tick (✓) two boxes.

14* A student investigates if a length of resistance wire has linear or non-linear behaviour.

They use the circuit shown in Fig. 14.1. Fig. 14.1

This is their method:

• Turn on the power supply.

• Measure the p.d. and current.

• Move slider on variable resistor.

• Take repeat measurements of p.d. and current.

Fig. 14.2 shows the student’s results.

Fig. 14.2

The student says, ‘I think my results are linear.’

Evaluate the student’s graph (Fig. 14.2) and conclusion.

Suggest how their method could be improved.

15* (a) A student investigates if resistance changes as current changes.

The student can use this equipment:

Describe the method the student should follow to work out if the resistance of the 10 cm wire changes as current changes and describe how to use the results to calculate resistance.

You can include a diagram in your answer.

The student writes a risk assessment for the investigation.

Suggest a possible hazard for this investigation.

How can the student reduce the risk from the hazard?

A student makes a ‘component tester’. He connects a diode to a small filament lamp.

This is a diagram of the component tester.

Describe how the student could use the component tester to find the positive (+) terminal of a cell.

Here is a graph of current against potential difference for a diode.

The diode is not a fixed resistor.

Describe two ways the graph shows this.

Calculate the resistance of the diode at + 0.8 V.

Use the graph and the equation: potential difference = current resistance

Resistance =........

The manufacturer of the diode gives the following warning:

The supply voltage must not exceed 1 V.

Use the graph in 16(b) to explain why.

Sketch a graph of current against potential difference for a filament lamp. Use the axes below.

A student makes a ‘component tester’. He connects a diode to a small filament lamp.

This is a diagram of the component tester.

Describe how the student could use the component tester to find the positive (+) terminal of a cell.

Here is a graph of current against potential difference for a diode.

The diode is not a fixed resistor.

Describe two ways the graph shows this.

Calculate the resistance of the diode at + 0.8 V.

Use the graph and the equation: potential difference = current × resistance

The manufacturer of the diode gives the following warning:

The supply voltage must not exceed 1 V.

Use the graph in 11(b) to explain why.

Sketch a graph of current against potential difference for a filament lamp. Use the axes below.

A student has one cell and two lamps. She wishes to connect them so that both lamps have maximum brightness.

Draw a complete circuit diagram to show how she can achieve this.

The student then investigates an unknown component. She records values for current through the component and the potential difference across the component.

Plot a graph of the data and draw a line of best fit.

One of the points has already been completed for you.

Describe what these results show.

Calculate the resistance of the unknown component.

Use the equation: Resistance = Potential difference ÷ Current

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