Electromagnetic induction - Maths questions

Maths questions often start with the command words 'calculate' or 'determine'. They will then have a blank space for you to show your working. It is important that you show your working, don't just write the answer down. You might earn marks for your working even if you get the answer incorrect.

Some maths questions might ask you to 'show that' something is true. These questions often require you to prove something mathematically. For example, you might have to calculate two values and then compare them.

In some maths questions you will be required to give the units. This may earn you an additional mark. Don't forget to check whether you need to do this.

Maths questions might include graphs and tables as well as calculations. Don't forget to take a ruler and calculator.

If drawing graphs, make sure you:

  1. put the independent variable on the x-axis and the dependent variable on the y-axis
  2. construct regular scales for the axes
  3. label the axes appropriately
  4. plot each point accurately
  5. draw a straight or curved line of best fit (you can use a special best fit line ruler to help with this)

If you are asked to calculate an answer and it has lots of significant figures, you should try to round it to the same number of significant figures you were given in the data in the question. Don't forget to check your rounding.

Edexcel questions courtesy of Pearson Education Ltd.

Sample question 1 - Higher

Question

A transformer is 100% efficient. It has 200 turns on the primary coil and 3,000 turns on the secondary coil. The input voltage is 55 V.

Show that the output voltage is about 800 V. [3 marks]

Select the equation which links pd and number of turns for a transformer:

\frac{V_p}{V_s} = \frac{N_p}{N_s}

Rearrange: \frac{V_s}{V_p} = \frac{N_s}{N_p}

\frac{V_s}{55} = \frac{3,000}{200}

\frac{V_s}{55} = 15


               {V_s}= 55 \times 15

V_s = 825~V

Remember in a 'show that' question you can’t use the number you are showing in your calculation.

Sample question 2 - Foundation and Higher

Question

A transformer is 100% efficient.

It has 200 turns on the primary coil and 3,000 turns on the secondary coil. The input voltage is 55 V and the output voltage is 825 V. Calculate the current in the secondary coil when the current in the primary coil is 0.50 A. [2 marks]

Select the equation which links pd and current for a transformer:

V_p I_p = V_s I_s

55 \times 0.5 = 825 \times I_s

275 = 825 \times I_s

Rearrange: I_s = 275 \div 825

I_s = 0.033~A