Last lesson - Electromagnetic induction If a magnet is moved inside a coil an electric current is induced (produced)

Electromagnetic induction A electric current is induced because the magnetic field around the coil is changing.

Generator/dynamo A generator works by rotating a coil in a magnetic field (or rotating a magnet in a coil). A slip-ring commutator produces alternating current (a.c.)

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Today’s lesson - Transformers 5

Transformers A transformer consists of 3 main parts

Transformers A changing current in the primary coil produces a changing magnetic field in the core. This changing magnetic field induces a changing current in the secondary coil.

Vp/Vs = Np/Ns Changing voltages The ratio of the number of turns on the coils equals the ratio of the voltages Vp/Vs = Np/Ns # of turns = Ns # of turns = Np

Changing voltages A transformer where the voltage rises is called a step-up transformer

Changing voltages A transformer where the voltage falls is called a step-down transformer

No energy for nothing However, no new energy is made

No energy for nothing Power in = power out VpIp = VsIs

a.c. only Because transformers rely on induction (changing fields), they only work with alternating current (a.c.)

Why do we need transformers?

Why do we need transformers? Current flowing through wires causes them to get hot and energy is lost.

Why do we need transformers? Keeping the current low means electricity can be transported long distances without losing too much energy.

Why do we need transformers? However, in order to send a large quantity of energy, high voltages are needed.

Transmission of Electricity Step-up Step-down