SherpaSherpa Logo

Induced Potential, Transformers & the National Grid Practice Questions

Question 1

5 marks

A student pushes the north pole of a bar magnet into a coil of wire. The coil is connected to a sensitive ammeter, as shown in the figure below.

SNpushcoilA

(a)

State what is seen on the ammeter while the magnet is being pushed into the coil.

(b)

The magnet is then held still inside the coil. Explain why the ammeter now reads zero.

(c)

Give two changes the student could make to increase the size of the current shown on the ammeter.

(d)

State what happens to the reading on the ammeter when the magnet is pulled back out of the coil at the same speed.

Question 2

5 marks

A transformer is used to operate a model railway from the 230 V230\,\mathrm{V} mains supply. The primary coil has 23002300 turns and the secondary coil has 120120 turns.

(a)

Describe the construction of a basic transformer and explain why the core is made of iron.

(b)

State whether this is a step-up or a step-down transformer. Give a reason for your answer.

(c)

Calculate the potential difference across the secondary coil.

Potential difference = .................... V\mathrm{V}

Question 3

3 marks

The table below gives the input and output potential differences for three transformers.

Transformer Potential difference across primary coil Potential difference across secondary coil
A 25 000 V25\,000\,\mathrm{V} 400 000 V400\,000\,\mathrm{V}
B 230 V230\,\mathrm{V} 6 V6\,\mathrm{V}
C 132 000 V132\,000\,\mathrm{V} 33 000 V33\,000\,\mathrm{V}
(a)

Which transformer is a step-up transformer? Give a reason for your answer.

(b)

The primary coil of transformer B has 34503450 turns. Calculate the number of turns on the secondary coil of transformer B.

Number of turns = ....................