Components in Series & Parallel Circuits (Edexcel GCSE Physics)

A student investigates resistors connected in parallel using a number of resistors.

Each resistor has the same resistance.

Figure 19 shows a circuit diagram with one resistor, R.

Figure 19

(i) Add to Figure 19:

• a voltmeter to find the potential difference across resistor R

• another resistor in parallel with resistor R.

[2]

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

[2]

(iii) 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 20 shows the results of the student’s investigation.

Figure 20

State the resistance of a single resistor.

resistance = .............................................................. Ω[1]

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

Use information from Figure 20 to support your answer.

[3]

A different circuit is then set up with two resistors as shown in Figure 21.

Figure 21

i) Calculate the potential difference across the 15 Ω resistor.

potential difference = ......................................... V[2]

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

Use the equation

P = I² × R

power produced ............................................ W[2]

Figure 18 shows identical filament lamps connected together to a 12V power supply.

Figure 18

(i) Calculate the potential difference across each lamp.

potential difference = ............................................... V[1]

(ii) The power output of each lamp is 0.75W

Calculate the resistance of each lamp.

resistance = ............................................... Ω[4]

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.

A student is investigating the I-V characteristic of a filament bulb. Figure 1 shows the circuit they set up to conduct the investigation.

Figure 1

The circuit shown in Figure 1 will not provide valid results. 

Identify one error the student has made and state how to rectify it.

The student plotted the graph shown in Figure 2 from her data.

Figure 2

Use words from the box to complete the following sentences.

As the potential difference increases, the current ............................., but the rate at which this occurs .............................This is because the temperature of the filament in the bulb ............................. with current.So the resistance ............................. causing the current to .............................

Which of the following steps is not a suitable safety procedure for this investigation?

Use the graph shown in Figure 2 to calculate the resistance of the filament lamp when the potential difference is 3 V.

Give your answer to an appropriate number of significant figures.

Figure 2

  resistance of filament lamp = .................................... Ω

Draw the circuit symbol for a light-dependent resistor (LDR).

Which of the following sketch graphs shows the IV characteristic of an LDR?

A	B
C	D

Explain how the shape of the graph in part (b) shows that the LDR is an ohmic conductor.

LDRs are used as light sensors to turn on lights as it gets dark outside.

Describe how the resistance of an LDR varies with light intensity.

Some students in a physics class are investigating the I-V characteristics of a fixed resistor.

The students are given the following equipment:

• An ammeter

• A voltmeter

• A variable resistor

• Fixed resistors of 100 Ω, 200 Ω, 400  and 500 Ω

• A power pack

• Wires

Draw a circuit using the equipment from the list that would enable the students to gather valid data.

Describe a method that would allow the students to obtain valid results.

The students plotted their data and produced the graph shown in Figure 1.

Figure 1

Write down an expression for the gradient of the graph in terms of resistance.

Use the graph to determine the resistance of the fixed resistor used by the students.

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