Electromagnetism - Transformers Question

7. (a) A student makes a transformer by winding coils of copper wire around a solidhard iron core.He carries out an experiment to show how the efficiency of the transformer varieswith the frequency of the supply. Describe the experiment, including the followingaspects in your answer• a sketch of the apparatus• the quantities which are kept constant• the procedure followed• the readings taken• how the efficiency is calculated.

Can someone post a diagram please? Or offer some help :smile:

bump

Original post by TheFarmerLad

Don't look at the question as if it were a test of your ability to remember facts, use the question to guide your thinking to develop a scientific approach.

1) What is efficiency? How would you measure efficiency for an electric circuit? What measurements are needed and what formula's would you use?

2) What would you use as a source of power given that the question states the frequency is varied?

3) How would you measure the output?

4) Think also about parameters that may be affected by your method and produce error. How would you minimise these?

Reply 3

TheFarmerLad

Original post by uberteknik

Thanks for the reply :smile:

I get the idea but I would like a definitive diagram as the markscheme doesn't provide one.

How have I done?

image 2.jpeg

Reply 4

uberteknik

Original post by TheFarmerLad

Thanks for the reply :smile:

I get the idea but I would like a definitive diagram as the markscheme doesn't provide one.

How have I done?

image 2.jpeg

Not bad. You need to include a method of measuring the voltages on both input and output.

You will also need some kind of load to limit the current of the output. The ammeter on the output will act as a short circuit if you don't. It also means you will need to make a statement stating that load has a power rating suitable for the experiment to avoid thermal problems as it's resistance increases with temperature.

(edited 8 years ago)

Reply 5

TheFarmerLad

Original post by uberteknik

Thank you!

Reply 6

uberteknik

Original post by TheFarmerLad

Thank you!

Also, one glaring error I just picked up, the questions says 'solid hard iron core'.

If the core is shaped as you have drawn it, then the core itself will act as a short circuit which will destroy the experiment.

Either draw the core with a very definite gap and say why you need the gap, or draw the core as a straight piece of metal like a rod with the windings either end.

Reply 7

TheFarmerLad

Original post by uberteknik

Could you post a diagram? It would make everything you're saying so much clearer :smile:

Reply 8

uberteknik

Original post by TheFarmerLad

Could you post a diagram? It would make everything you're saying so much clearer :smile:

Actually, ignore my last comment. It's above A-level and the question refers to a solid hard iron core, so your diagram is perfectly OK.

Just add a resistive load (R) across the output terminals and place a parallel voltmeter across that load. Remember to add a voltmeter across the input terminals as well.