Exam Question

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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.

 
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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

So your guesswork was correct

 
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