**The
Transformer: Example Questions **

**Example 1**

N_{s} is the unknown.

We therefore have to arrange the equation as follows:

N_{s }/ 600 = 200/20
= 10

So, N_{s }= 600 x
10 = 6000 (no unit as you are working out the number of turns)

In tests and examinations you must show your calculation
in full in an examination to show that you understand how to use it.

There is a **quick way **to analyse this circuit
and it is handy to do this as a quick check.

Look at the ratio relationship between the voltages
and turns they will be the same for each.

**Example
2 **

This time V_{s} is the unknown.

We therefore have to arrange the equation as follows:

V_{s }/ 6 = 2000/50
= 40

So, V_{s }= 6 x 40
= 240 volts (don't forget the unit!)

Let's try the check again

**Example 3 **

Now we have V_{p} as the unknown.

We therefore have to arrange the equation as follows:

V_{p }/ 12 = 3500/100
= 35

So, V_{p }= 12 x 35
= 420 volts (unit omission loses you marks!)

A quick check:

**Example 4 **

Finally N_{P }as the unknown

We must arrange the equation so N_{P }is at
the top left

N_{P }/ 150 = 230/12 = 19.17 (not a simple ratio
here!)

So, N_{p }= 150 x 19.17 = 2876 (to the nearest
turn… you can't have part turns!).

This is more difficult to do our 'quick-check' way - but still possible!

Try some questions
or try to complete the transformer crossword.

See the National
Grid for how transformers are used in power distribution. You will
also be used to using one to charge up your mobile phone from the mains!.