Transformers

Front 1

Outline the Essential features of a step down transformer when in operation

Back 1

Primary coil with more turns and secondary coil

Alternating current to produce a change in magnetic flux

Coils wound around a core

Front 2

Describe causes of energy losses in a transformer and discuss how these energy losses may be reduced by suitable design and choice of materials (6)

Back 2

Eddy currents are as a result of Lenz's law where the direction of the induced emf is always to oppose the change in the field that caused it (current induced in opposite direction) , causing heating in the transformer.

Reduced: laminating the core instead of having a continuous solid core/ iron core components separated by very thin layers of insulator which reduces currents as they cannot flow in conductor that is discontinuous. Increasing the resistance of the core as currents cannot flow in a conductor that has a high resistance

Electrical heating from the wires in the coil having some resistance and the current causing heating of the coils.

Reduced: using low resistance THICK wire for the coils (most important for the secondary coil of the step down transformer as it has the highest current through it)

AC current has to magnetise and demagnetise the core continually in opposite directions- energy is required to do this and is wasted in heating the core

Reduced: using magnetically soft materials such as iron which can more easily be magnetised and demagnetized.

Front 3

How to make a transformer more efficient

Back 3

The greatest amount of the magnetic flux created by the (current through the) primary coil must pass through the secondary coil

This will not happen if the coils are widely separated from each other

This can be made more efficient by having the coils close together

Front 4

Emf Proportional to

Back 4

rate of change of flux linkage

Front 5

Lenz's Law

Back 5

The direction of the induced EMF (and current) is always to oppose the change in the magnetic field that caused it