Transformers

Question 1

Which coil do step-down transformers have more turns on?

Answer 1

Step-down transformers have more turns on the primary coil than on the secondary coil

Question 2

True or false? The national grid efficiently transfers energy by transmitting electricity at a high current and a low potential difference.

Answer 2

False

It transfers energy efficiently by using a high potential difference and a low current

Question 3

Describe how step-up and step-down transformers are used in the national grid

Answer 3

Step-up transformers are used to increase the potential difference of the electricity supply before it is transmitted across the national grid (so energy is transmitted efficiently). Step-down transformers are used to bring the potential difference back down to safe, usable levels for consumers

Question 4

The primary coil of a step-up transformer has an alternating p.d. of 3 V across it and a current of 15 A through it. Across the secondary coil, the p.d. is 9 V. The transformer is 100% efficient. Calculate the current through the secondary coil using the equation:

p.d across primary coil x current through primary coil = p.d across secondary coil x current through secondary coil

Answer 4

5A
Substitute the values into the given equation: 3 x 15 = 9 x current through secondary coil
Current though secondary coil = (3 x 15) / 9 = 45 / 9 = 5A

Question 5

Explain how applying an alternating potential difference across the primary coil of a transformer induces an alternating p.d across the secondary coil

Answer 5

The alternating p.d across the primary coil produces an alternating magnetic field. The core is magnetic, so the alternating magnetic field causes the magnetisation of the iron core between the two coils alternate too, and this changing magnetic field induces a p.d. across the secondary coil