Transformers

What frequencies do switch mode transformers operate

Between 50kHz and 200kHz.

What do step up transformers do.

Step up the voltage. Have more turns on the secondary coil than the primary coil.

In secondary coil the potential difference across it is greater than in a primary coil. In a

Step up transformer.

What feels this rapidly changing magnetic field

The secondary coil.

The two most important types of transformers are....

-step up transformers -step down transformers Both have two coils, the primary and the secondary, joined with an iron core.

What are switch mode transformers

A type of transformer that operate at higher frequencies than traditional transformers.

What does changing field induce

An alternating potential difference across the secondary coil( with the same frequency as the alternating current in the primary). Electromagnetic induction of potential difference in fact.

Why is the field in the iron core constantly changing.

Because there is alternating current (AC) in the primary coil. (100 times a second if it's at 50Hz). I.e it's a changing magnetic field.

What does the iron core carry?

Magnetic field not current

By there being no changing field there

No potential difference

Transformers only work with AC current

Not DC current.

What happens if you supply DC to the primary

Nothing comes out of the secondary at all. There will be a angelic field in the iron core. But it doesn't constantly change.

Potential difference across primary coil -----------------------------= Potential difference across secondary coil

Number of turns on primary coil ----------------------------------- Number of turns on secondary coil.

What is the formula for power supplied

Power= current *potential difference P=I*V

In step down transformers

The p.d across the secondary coil is less than the p.d across the primary coil.

Transformers work by electromagnetic induction when

The primary coil produces a magnetic field that stays within the iron core. This means almost all of it passes through the secondary coil and hardly any is lost.

What determines whether the potential difference induced in the secondary coil is greater or less than the potential difference in the primary.

The relative number of turns on the two coils.

What is the benefit of switch mode transformers working at higher frequencies

They can be much lighter and smaller than traditional transformers that work from a 50KHz mains supplies

What do step up transformers do.

They step down the voltage. They have more turns on the primary coil than the secondary.

Why are switch mode transformers more efficient than other types of transformers

They use very little power when switched on with no load is applied.

What is the iron core used for

Transferring the changing magnetic field from the primary coil to the secondary. No electric flows around the iron core.

What are transformers?

Use electromagnetic induction to change the potential difference(p.d). So they will only work on AC

You can write electrical power input =electrical power output as

V p I p=V s I s Vp=potential difference across primary coil Ip= current in the primary coil in volts Vs= p.d across secondary coil Is= current in the secondary