Transformers

Question 1

What happens if a wire cuts through a magnetic field?

Answer 1

potential difference is induced across the ends of the conductor

if the wire is part of a complete circuit an electric current will flow in the circuit

Question 2

What does an a.c. in the primary coil of a transformer produce?

Answer 2

it produces a changing magnetic field in the iron core, and hence the secondary coil

this induces an alternating potential difference across the ends of the secondary coil

Question 3

What happens in a step-up transformer?

Answer 3

the p.d. across the secondary coil is greater than the p.d. across the primary coil

the opposite happens with a step-down transformer

Question 4

What happens if a transformer is 100% efficient?

Answer 4

the electrical power output would equal the power input

Question 5

What frequency do switch mode transformers operate at and how do they work?

Answer 5

between 50kHz and 200kHz

they are used because some devices need a smaller p.d. than the 230 V from mains electricity

switch mode transformers use complex electronic circuit, that switch the current on and off rapidly

causing the alternating current to be changed to a high frequency, this reduces p.d.