# Electricity - Section B - Maths questions

Don't forget to take a ruler and calculator into the exam.

Maths questions often start with the command words like Calculate, Determine, Estimate and Measure. They will then include blank space for you to show your working.

When an answer to a maths question is marked:

• marks are given for working, including substitution and rearrangement
• errors carried forward are taken into account

Errors carried forward is to do with what happens if a later answer depends on an earlier answer, and you get the earlier one wrong. You could still get full marks in the later answer if your working is correct but you use the incorrect earlier answer.

If your answer has many decimal places or figures, make sure you give it to an appropriate number of decimal places or significant figures. You may be asked to give units. This may earn you an additional mark, so don't forget to check whether you need to do this.

Some maths questions might ask you to plot or complete a graph or table. When you draw a graph, make sure you:

1. plot each point accurately
2. draw a best fit straight line or curve

You may be given a grid with axes and scales already given. Sometimes you may be given an empty grid for you to supply your own axes. When you do this:

• put the independent variable on the x-axis and the dependent variable on the y-axis
• make sensible scales so that the plotted points cover at least 50% of the area of the graph
• label the axes with their quantity and unit, eg time (s)

## Sample question 1 - Foundation

Question

A student finds a resistor which has no markings on it.

The student uses a voltmeter, an ammeter and a cell to find the resistance of the resistor.

In the experiment the current reading is 0.15 A and the potential difference is 2.0 V.

Calculate the resistance of the unknown resistor.

Use the formula potential difference = current × resistance

OCR Gateway Science, GCE Physics, Paper J249, 2016.

2.0 ÷ 0.15 = 13.3 Ω

3 significant figures (i.e. not 13.333 Ω, etc)

## Sample question 2 - Foundation

Question

A current of 1.5 mA flows in a circuit.

Calculate the charged transferred by this current in 200 s.

State the unit. [3 marks]

This question has been written by a Bitesize consultant as a suggestion to the type of question that may appear in an exam paper.

1.5 mA = 1.5 ÷ 1,000 = 0.0015 A

charge = 0.0015 × 200 = 0.3 C / coulombs

## Sample question 3 - Higher

Question

The rate of flow of electrical charge in a circuit is a current.

A current of 40 mA transfers a charge of 3.6 C. Calculate how long this takes.

OCR Gateway Science, GCE Physics, Paper J249, 2016 - Higher.

40 mA = 0.04 A

rearrange Q = I × t … t = Q/I

t = 3.6 ÷ 0.04

t = 90 s

## Sample question 4 - Higher

Question

A student takes voltage and current measurements for four resistors.

The table shows the results from this experiment.

ResistorVoltage (V)Current (A)Resistance (Ω)
A12.02.0
B6.01.5
C7.51.5
D8.02.0

a) Which two resistors have the same resistance value? Use the data to show this. [2 marks]

b) Calculate the maximum resistance that can be made using all four resistors. [1 mark]

OCR Gateway Science, GCE Physics, Paper J249, 2016 - Higher.

a) B and D

resistance = voltage ÷ current

A = 6 Ω, B = 4 Ω, C = 5 Ω, D = 4 Ω

b) (6 + 4 + 5 + 4) = 19 Ω