Components in Series & Parallel Circuits (Edexcel IGCSE Physics)

A student is given an unknown electrical component, X. He uses a circuit to investigate how the current in X varies with the voltage across it.

Which of these circuits is correct for his investigation?

This diagram shows another circuit the student is investigating.

(i) Complete the table by putting a tick (✓) in the box if the lamp is lit and a cross (х) in the box if the lamp is not lit.

(ii) Suggest where this circuit would be useful in a house.

A student uses voltmeter and ammeter readings to find the resistance at different temperatures. One set of readings is show below.

(i) State the equation linking voltage, current and resistance.

(ii) Show that the resistance of the thermistor at 80 °C is about 5000 Ω.

A student uses voltmeter and ammeter readings to find the resistance at different temperatures for two different components, A and B.

The graphs show the results.

Compare the results for component A and component B.

An LED needs a minimum voltage to make it emit light.

The student investigates this minimum voltage using the circuit shown.

The student uses a voltmeter to measure the voltage across the LED.

Add this voltmeter to the circuit diagram.

The student gradually increases the voltage across the LED and records the minimum voltage at which the LED emits light. The results for some different LEDs are shown in the table.

Plot the results of the student's investigation on the grid.

The student concludes:

Evaluate the student's conclusion.

The diagram shows part of an electric circuit.

Complete the circuit diagram by adding:

• a resistor in series with the lamp and battery

  • a second lamp in parallel with the first lamp

  • a voltmeter that measures the voltage across the resistor

  • an ammeter that measures the current in the resistor

The current in a resistor is measured for different voltages.

The table shows the results.

(i) Plot a graph of this data on the grid.

(ii) Circle the anomalous point on the graph.

(iii) Draw a line of best fit.

(i) State the equation linking voltage current and resistance.

(ii) Use your graph to find a value for the resistance of the resistor.

resistance = ............................................... Ω

The graph shows how current and voltage vary for a filament lamp.

Draw a circuit diagram to show how you should connect the equipment needed to make the measurements needed to plot the graph.

The resistance of the filament lamp changes as the voltage is increased.

(i) How can you tell this from the graph?

(ii) Explain these changes in resistance.

A student investigates how the resistance of a piece of wire changes with voltage across the wire.

The student connects an ammeter, a voltmeter, a battery, a variable resistor and the wire in an electrical circuit.

(i) Complete the diagram to show how the student should connect the circuit.

(ii) Describe what she should do to obtain a set of results for her investigation.

The student keeps the temperature of the wire constant during the investigation.

Suggest why she does this.

When the student looks at her results, she notices that the voltage across the wire is directly proportion to the current in it.

(i) State the relationship linking voltage, current and resistance.

(ii) The student calculates the resistance and then plots a graph of resistance against voltage.

On the axes, sketch the shape of her graph. 

A student plans to measure the resistance of a piece of wire. He sets up this circuit and finds that it does not work.

Identify the three errors in the student’s circuit.

The student uses a correct circuit to obtain these results.

Plot a graph to show the relationship between current and voltage for the wire.

(i) Find the current when the voltage is 2.5 V.

(ii) Suggest why the line on the graph curves.

Describe what else the student should do to find an accurate value for the resistance of the piece of wire at a constant temperature.

A student is given an unknown electrical component, X. He uses a circuit to investigate how the current in X varies with the voltage across it.

The table shows the student’s results.

Plot a graph of these results and draw a curve of best fit.

(i) State the equation linking voltage, current and resistance.

(ii) Calculate the resistance of component X when the voltage across it is 10.0 V.

Give the unit.

Resistance = ................................ unit ......................

(i) Describe the pattern shown by the graph from part (a).

(ii) Suggest a conclusion for the investigation

A student uses a circuit that contains an ammeter, a battery, a light emitting diode (LED) and a voltmeter.

He notices there is no current in the diode when the battery is reversed. 

He replaces the battery with an a.c. supply.

Which graph shows how the current in the diode varies with time?

The student shines light on the LDR through a circular hole in a piece of black card, as shown in the diagram.

The student repeats the experiment using cards with holes of different diameter. The distance from the card to the LDR is always 5 cm.

The student varies the current in the circuit by adjusting the variable resistor.

The independent variable in this experiment is:

A student uses this apparatus to investigate how the resistance of a thermistor changes with temperature.

(i) Draw a circuit diagram for this investigation.

(ii) The student wants to measure the voltage across the thermistor.

On your diagram, add a symbol to show how she should connect the voltmeter to the circuit.

(iii) Explain how the student can use the apparatus to investigate how the resistance of the thermistor varies with temperature between 0 °C and 100 °C.

The graph shows the student’s results.

Two students discuss the line of best fit for this graph. One student thinks it is the curved line A. The other student thinks that it is the straight line B.

(i) Suggest which line is better, giving a reason for your choice. 

(ii) Suggest why measuring the resistance of the thermistor at 10 °C could help to decide which line is better.

These graphs show the voltage (V) changes with the current (I) for three components.

The components are a metal wire at a constant temperature, a diode and a filament lamp.

Which letter represents the correct graph for each component?

(i) Metal wire at constant temperature

(ii) Diode

(iii) Filament lamp

A student uses the following apparatus to investigate how the resistance of a thermistor changes with temperature.

Explain why the student places the thermistor in a beaker of water.

The table shows the student's results.

(i) Plot a graph of these results on the grid.

(ii) Circle the anomalous point on the graph.

(iii) Draw a curve of best fit.

(i) Why is the maximum temperature in the student’s investigation limited to 100°C?

(ii) Suggest how the student obtains readings below room temperature.

The resistance of a Light Dependent Resistor (LDR) is affected by the amount of light that shines on it. 

A student investigates this relationship using the circuit shown.

(i) The student uses a voltmeter to measure the voltage across the LDR.

Add this voltmeter to the circuit diagram.

(ii) Explain how the student can work out the resistance of the LDR using this circuit.

The student shines light on the LDR through a circular hole in a piece of black card, as shown in the diagram. The student repeats the experiment using cards with holes of different diameter. The distance from the card to the LDR is always 5 cm. The student varies the current in the circuit by adjusting the variable resistor.

The photograph shows how the student places a metal ruler to measure the diameter of one of the holes.

Suggest how the student can improve this technique while still using the same ruler.

The table shows the student’s results.

(i) Plot the student’s results on the grid.

(ii) Draw a curve of best fit on the graph.

(iii) Describe the relationship between the resistance of the LDR and the diameter of the hole.

A student investigates the current in a thermistor at different temperatures using the circuit shown in the diagram.

The student uses a voltmeter to check that the voltage across the thermistor stays constant throughout the investigation.

(i) Add this voltmeter to the circuit diagram.

(ii) Give a reason for keeping the voltage across the thermistor constant.

(iii) Give a reason for including the variable resistor in the circuit.

The student increases the temperature of the thermistor and records the current and temperature readings. The graph shows the student's results.

The student plans the use his circuit to make an electronic thermometer, He notices that both the scales on the graph go up to 100.

He thinks that the current reading, measured in mA, gives a direct indication of the temperature measured in °C. He labels the ammeter's scale 'temperature in °C'.

Give three reasons why the student's electronic thermometer is unlikely to show the correct temperature.

You may use information from the circuit and the graph to support your answer.