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What happens if a wire cuts through a magnetic field?

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


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

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


What happens in a step-up transformer?

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


What happens if a transformer is 100% efficient?

the electrical power output would equal the power input


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

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.