(6.17P-6.20P) Transformers

What is a transformer?

A device used to change the value of an alternating current/voltage

What is the structure of a transformer?

A rectangular iron core with:

• a primary coil

• a secondary coil

How does a transformer work?

An a.c. supplied to primary coil

• producing a changing magnetic field around it

• causing a changing magnetic field through the soft magnetic core

• which interact with the secondary coil

• inducing a alternating p.d in the secondary coil

How do transformers change the size of an alternating p.d.?

By having a different number of turns on the input and output sides of the magnet

What does a step-up transformer do + look like?

Increases the voltage

It has more turns on the secondary than the primary coil

What does a step-down transformer do + look like?

Decreases the voltage

It has more turns on the primary than the secondary coil

Why and how are transformers used in electricity transmission?

Step-up transformers are used after the power station

• to reduce energy loss via heat

  • high current = heating the wire

• P=IV so increasing the voltage = decreasing the current for the same P

• electricity is transferred at high voltages, increasing efficiency

Step-down transformers are used before use

• to reduce voltage + increase current

  • down to mains (230V) for safety (fuses etc.)

State the transformer equation.

voltage of the primary / voltage of the secondary = no. of turns on the primary / no. of turns on the secondary

Vp/Vs = Np/Ns

these fractions can be flipped

State the ideal transformer equation.

Voltage of primary * current of primary = voltage of secondary * current of secondary

Vp * Ip = Vs * Is