CP11 - Electromagnetic induction

How can a magnet be used to produce an electrical current?

Electromagnetic induction - Change a magnetic field inside a coil of wire.

How to change magnetic field in a coil?

Move magnet magnet back and forward, spin the coil in a uniform field.

How to increase size of current produced?

Increase speed at which magnet moves past coil, increase magnet strength.

How to change direction of a current?

Move the magnet in the opposite direction.

Alternator/dynamo

A coil of wire that is rotated inside a magnetic field. A PD is induced in the wire. The ends of the loop are connected to split rings and produce alternating/direct current (alternator or dynamo)

What do microphones do?

Covert pressure variations into current.

What do loudspeakers do?

Convert variations in electrical current into sound waves.

Transformer

Two coils of insulated wire wound onto an iron core. There is no electrical connection between the two coils of wire.

Step-up and step-down transformer

Increases the voltage (and decreases the current).

Decreases the voltage (and increases the current).

How does a transformer work?

An alternating current in the primary coil produces a changing magnetic field in the secondary coil.

What is the transformer turns ratio equation?

Vp/Vs = Np/Ns = Is/Ip (N is turns, V is voltage, I is current (s & p subscriptions for secondary and primary)).

Why is electricity transferred at high voltages?

Current is lower and so less energy is lost due to heating of the transmission lines.

Power equation for transformers with 100% efficiency?

VpIp = VsIs