The
Transformer: Example Questions
Example 1
N
s is the unknown.
We therefore have to arrange the equation as follows:
Ns / 600 = 200/20
= 10
So, Ns = 600 x
10 = 6000 (no unit as you are working out the number of turns)
In tests and examinations y ou 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:
Vs / 6 = 2000/50
= 40
So, Vs = 6 x 40
= 240 volts (don't forget the unit!)
Lets try the check again
Example 3
Now we have V
p as the unknown.
We therefore have to arrange the equation as follows:
Vp / 12 = 3500/100
= 35
So, Vp = 12 x 35
= 420 volts (unit omission loses you marks!)
A quick check:
Example 4
Finally NP 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.
Here
is a link to School Science for more background reading on transformers
and a little interactive quiz.
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!.