Resistors and I-V characteristics

A student connects a resistor across the terminals of a 9 V battery.

There is a current of 6 mA in the resistor.

Calculate the resistance of the resistor.

Describe how an additional component could be used to vary the current in the resistor.

A voltmeter has four different scales.

Which one of these scales would be most suitable to measure a voltage of 0.85 V?

*(c) The table in Figure 14 gives some information about series and parallel circuits.

Describe how a student can use ammeters and voltmeters to investigate the information given in Figure 14.

Your answer should include

• circuit diagrams showing how the currents and voltages can be measured

• a comparison of the results that would be expected

Space for circuit diagrams

Answer lines for this question are on page 27.

A student investigates how current varies with potential difference across a filament lamp.

The student uses a power supply, a variable resistor, the filament lamp and two meters.

Part of the circuit diagram is shown in Figure 10.

Complete the circuit diagram needed for this investigation.

Figure 10

Another student repeats the investigation in part (a) using a data logger.

The data logger records observations using sensors instead of meters. The sensors are connected to a computer to collect and display the observations.

The data logger collects 555 pairs of data in 2 minutes.

The results are shown in Figure 11.

Suggest one advantage of using a data logger instead of meters in this investigation.

Describe how current varies with potential difference in the graph in Figure 11.

Use data from the graph in Figure 11 to show how the resistance changes with potential difference for the filament lamp.

Which of these equations is correct?

The unit of work is the joule.

Starting with the meaning of work, we may obtain an equivalent unit of work as Nm.

Using work F d

unit of work unit of force unit of distance Nm

The unit of potential difference is the volt.

Explain how, starting with the meaning of potential difference, we may obtain an equivalent unit of potential difference.

Figure 9 shows a lamp connected to a d.c. power supply.

The power supply provides a potential difference (voltage) of 4.5 V.

The current in the lamp is 0.30 A.

Calculate the resistance of the lamp.

Use the equation

resistance =_........ Ω

Calculate the power supplied to the lamp.

power =_........ W

Another identical lamp is added to the circuit, as shown in Figure 10.

The power supply provides the same potential difference as it provided in the circuit in Figure 9.

State and explain the difference between the brightness of the lamp in Figure 9 and the brightness of a lamp in Figure 10.

A student is given a low voltage power supply and 1 m of resistance wire.

The student uses these and other pieces of equipment to measure the resistance of just 50 cm of the resistance wire.

Draw a diagram of the circuit that the student should use.

Your circuit diagram should identify the pieces of equipment that the student uses.

Describe the difference between direct current (d.c.) and alternating current (a.c.) in electrical circuits.

Figure 1 shows a lamp connected to a d.c. power supply.

The power supply provides a potential difference (voltage) of 4.5 V.

The current in the lamp is 0.30 A.

Calculate the resistance of the lamp.

Use the equation

resistance =_........ Ω

Calculate the power supplied to the lamp.

power =_........ W

Another identical lamp is added to the circuit, as shown in Figure 2.

The power supply provides the same potential difference as it provided in the circuit in Figure 1.

State and explain the difference between the brightness of the lamp in Figure 1 and the brightness of a lamp in Figure 2.

A student is given a low voltage power supply and 1 m of resistance wire.

The student uses these and other pieces of equipment to measure the resistance of just 50 cm of the resistance wire.

Draw a diagram of the circuit that the student should use.

Your circuit diagram should identify the pieces of equipment that the student uses.

Which of these shows the correct circuit symbol for a thermistor?

A student investigates how the resistance of a thermistor varies with temperature.

Figure 7 shows a graph of the results of this investigation.

Describe how the resistance of this thermistor varies with temperature.

Draw the tangent to the curve at a temperature of 30 °C, to find the rate of change of resistance with temperature at 30 °C.

State the unit.

rate of change of resistance with temperature at 30 °C =_........ unit_........

Figure 8 shows the apparatus used for this investigation.

Explain one improvement in measurement that the student could make in the investigation.

In this investigation, the resistance can be measured in two ways.

Method 1 – use an ohmmeter.

Method 2 – use an ammeter and a voltmeter.

Method 1
Method 2

using an ohmmeter
using an ammeter and voltmeter

Figure 9

Explain why method 2 gives more precise results than method 1.

Figure 10 shows two different types of the same circuit component.

What is the name of this circuit component?

Which row in the table describes the way that ammeters and voltmeters should be connected with a component in a circuit?

Figure 11 shows the results from an experiment where the potential difference (voltage) across a filament lamp was varied.

The current and voltage were measured.

Describe the relationship between the current and the voltage as shown in the graph in Figure 11.

Use the values of the voltage and current at point P and at point Q on the graph in Figure 11 to complete the table in Figure 12.

Calculate the resistance of the filament lamp when the voltage is 4.5 V and the current is 51 mA.

Use the equation

resistance =_........ Ω

Explain why the resistance of the filament lamp changes as the voltage across it increases.

Figure 1 shows the results from an experiment where the potential difference (voltage) across a filament lamp was varied.

The current and voltage were measured.

Describe the relationship between the current and the voltage as shown in the graph in Figure 1.

Use the values of the voltage and current at point P and at point Q on the graph in Figure 1 to complete the table in Figure 2.

Calculate the resistance of the filament lamp when the voltage is 4.5 V and the current is 51 mA.

Use the equation

resistance =_........ Ω

Explain why the resistance of the filament lamp changes as the voltage across it increases.

A student investigates resistors connected in parallel using a number of resistors. Each resistor has the same resistance.

Figure 10 shows a circuit diagram with one resistor, R.

Add to Figure 10:

a voltmeter to find the potential difference across resistor R

another resistor in parallel with resistor R.

State the measurements that the student must take to find the overall resistance of the resistors in parallel.

The student investigates how the overall resistance of the circuit changes when additional resistors are added in parallel to R.

Each resistor has the same resistance.

Figure 11 shows the results of the student’s investigation.

State the resistance of a single resistor.

resistance =_........ Ω

Comment on the relationship between the overall resistance of the circuit and the number of resistors in parallel.

Use information from Figure 11 to support your answer.

A different circuit is then set up with two resistors as shown in Figure 12.

Calculate the potential difference across the 15 Ω resistor.

potential difference =_........ V

Calculate the total power dissipated when there is a current of 0.20 A in the two resistors.

Use the equation

power produced_........ W

Which of these symbols is used to represent a thermistor in an electrical circuit?

A student investigates how the current in a lamp changes with the potential difference across the lamp.

The student uses the results to calculate the resistance of the lamp.

The results are shown in the table in Figure 9.

One value of resistance is missing from the table in Figure 9.

Calculate the value of resistance that is missing from the table.

missing resistance =_........ Ω

The student writes this conclusion:

‘The resistance of the lamp is directly proportional to the potential difference.’

Comment on the student’s conclusion. Use information from Figure 9 in your answer.

*(c) Figure 10 shows a battery connected to a filament lamp.

Explain, in terms of the movement of charged particles, how energy is transferred from the battery, through the lamp, to the surroundings.

Which of these symbols is used to represent a thermistor in an electrical circuit?

A student investigates how the current in a lamp changes with the potential difference across the lamp.

The student uses the results to calculate the resistance of the lamp.

The results are shown in the table in Figure 2.

One value of resistance is missing from the table in Figure 2.

Calculate the value of resistance that is missing from the table.

missing resistance =_........ Ω

The student writes this conclusion:

‘The resistance of the lamp is directly proportional to the potential difference.’

Comment on the student’s conclusion. Use information from Figure 2 in your answer.

The student used a power supply that had fixed output voltage settings. Each of these outputs was a whole number of volts.

Describe how the student could add a component to the circuit that would provide a continuously variable voltage across the lamp.

Figure 6 shows a graph of current against potential difference for an electrical component.

Which electrical component will show this variation of current with potential difference?

A lamp is connected to a potential difference of 0.24 V.

The current in the lamp is 0.12 A.

Calculate the power of the lamp.

Use the equation

P = I × V

power of the lamp =_........ W

The potential difference is changed to 0.30 V. The current in the lamp is now 0.13 A.

The lamp is switched on for 35 s.

Calculate the energy that is transferred in this time. Select an equation from the list of equations at the end of this paper.

energy transferred =_........ J

The current in the lamp stays at 0.13 A.

Calculate the charge that flows through the lamp in 35 s. Use the equation

Q = I × t

charge =_........ C

A student measures the current in the lamp for several values of potential difference across the lamp.

Figure 7 shows the student’s results.

The student uses the results in Figure 7 to write this conclusion.

‘ As the potential difference across the lamp increases, the current in the lamp increases and the relationship is directly proportional.’

Comment on the student’s conclusion.

Figure 8 shows identical filament lamps connected together to a 12 V power supply.

Calculate the potential difference across each lamp.

potential difference =_........ V

The power output of each lamp is 0.75 W

Calculate the resistance of each lamp.

resistance =_........ Ω

*(b) Explain, with the aid of a circuit diagram, the method a student could use to investigate how the resistance of a single lamp changes with the potential difference across the lamp.