Exam Question Help Support Talk Electrician Forum: misssweden

DNO Official™
Hi guys.

I would be really grateful if you could help to explain an exam question that I got stuck on earlier. I did ask my teacher but he just said that although we've learnt about magnetic fields we haven't gone through that bit yet.

The question was:

In a magnetic circuit the magnetic field strength H is expressed in ampere turns/metre. H is calculated using the formula

a) H=i/nl

b) H=ni/l

c) H=il/n

d) H=nl/i

I guessed option b), on the basis that I was thinking "something current divided by length". But I'm not sure if it's right. If you could please explain this to me that would be great.

Thank you.

Tutor 1

Tutor
Hello Miss Sweden

Magnetic Field Strength (H) is generally the magnetomotive force per unit length of a magnetic circuit

Often expressed in amperes per metre (A/m) - which is often spoken as "'ampere turns per metre".

The correct equation is

H = (in) / l

where:
H = magnetic field strength (ampere per metre)
i = current flowing through the coil (amperes)
n = number of turns in the coil
l = length of the magnetic circuit

misssweden

DNO Official™
Thank you very much Tutor 1! I'm glad I was on the right track, however you explanation makes a lot more sense than my rough guess.

Thanks again.