# Physics Unit 3

physics

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## electromagnetic induction

The creation of a voltage in a wire which is experiencing a change in magnetic field

by moving a magnet in a coil of wire or moving conductor in a magnetic field

magnetic in opposite direction, voltage/current reversed

magnet/coilmoving backward and fowards, produces voltage that keeps swapping directions

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## Transformers

Transformers change AC voltages

step up and step down transformers, both have two coils, the primary and the secondary

step up - steps the voltage up, more turns on the secondary coil

step down - steps the voltage down, more turns on the primary coil

primary coil -> magnetic field

alternating current in primary coil -> field constantly changing direction

rapidly changing magnetic field felt by the secondary coil

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## Transformers 2

primary voltage     = number of turns on primary

secondary voltage = number of turns on secondary

used on the national grid:

to transmit a lot of power, need high voltage or current

high current -> loss of power (as heat) -> resistance of the cables

cheaper -> voltage up to 400,000 V -> current very low

transformers step up the voltage at one end for efficient transmission, and steps it down at the other end, to safe usable levels

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