You are Here: Home >< Physics

# Electromagnetic Induction Question Watch

1. Hey,

How do the formulae,

induced emf = (-) rate of change of magnetic flux linkage

and

induced emf = BANwsin(wt)

corroborate each other?

I.e. let's say a coil rotates 90 degrees. Hence, the change in induced emf would be its maximum value. According to the second equation, this would be BANw.

Hence, from the second equation, induced emf = BANw = BAN(2pie)/T

However, when looking at the first equation: through the 90 degree rotation, the change in magnetic flux linkage would also equal its maximum value, which is BAN.

Hence, from first equation, induced emf = BAN/T

Therefore the two equations do not lead to the same result???
2. I think I have answer to the question. They will lead to the same result. You aren't looking at it right. Farradays law states that the induced emf is the Rate of change of flux linkage. Your equation doesn't show that. You said emf = BAN / T which is wrong. Emf = N ΔΦ /ΔT (where ΔΦ is the change of flux BA).

Some more insight. The flux linkage will change continously in a rotating coil. So NΦ = BAN cos(2π ft) where 2π ft = angle.
The diffrential of this with respect to time gives :

N ΔΦ /ΔT = (-)BAN(2π f) sin(2π ft)

This is your second equation. The gradient of a graph with flux lnikage of rotating coil against time is the emf. So they will give the same value. You are reading it wrong that's all. I hope that helps.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: May 30, 2016
Today on TSR

...in schools

### I think I'm transgender AMA

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.