USING TRANSFORMERS TO CHANGE VOLTAGES

4 marks · Normal

Figure 1 shows a transformer used to supply power to a small device.

Figure 1. Transformer structure.

(a)

Label the primary and secondary coils on Figure 1.

[1 mark]

(b)

Explain why the core is made from soft iron and not another material.

[3 marks]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

(a) A is Primary coil, B is Secondary coil. · must show Primary and Secondary clearly labeled on diagram

(b) Soft iron is used because it is easily magnetised and demagnetised, has high magnetic permeability, and efficiently channels the changing magnetic field. This reduces energy losses and increases transformer efficiency. · must show Soft iron can be magnetised/demagnetised easily, Reduces energy loss/increases efficiency, Channels changing field better than other materials

Must show: labels on A: Primary, B: Secondary, core: high permeability, core: easy magnetise/demagnetise, core: reduces energy loss

Also accept: Named efficiency improvement

Common mistakes: Confusing steel with soft iron

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · Correctly labels primary and secondary coils.

B2 (b) · 1 mark · Explains soft iron is easily magnetised/demagnetised.

B3 (b) · 1 mark · Mentions reduces energy losses/increases efficiency.

B4 (b) · 1 mark · Mentions soft iron channels changing field better than other materials.

Worked solution

Figure 1 with labels.

b) Soft iron is used for the transformer core because it is easy to magnetise and demagnetise each cycle, which reduces energy lost as heat and makes the transformer more efficient.