# Homework Help: Magnitude of EMF when the armature coil is in different positions?

1. Jun 22, 2014

### Dreaam

I am currently studying for a Magnetism and Electricity exam coming up. I was just wondering, within the topic of Electromagnetic induction; my textbook states that if an armature coil of some sort -either from an AC or DC generator was placed horizontally into a magnetic field that is also horizontal, (so the North pole on the left and south pole on the right, meaning the magnetic field lines would be going --->), then the EMF would be at a maximum. If the coil was vertical the EMF would be a minimum. This picture may explain it better: http://www.rfcafe.com/references/El...ourses/images/electricity-navy-basics-126.jpg

I unfortunately don't understand this and there is no further explanation other than those statements. Could somebody please explain to me why the EMF would be a maximum when the armature coil is horizontal.

Relevant formulas

EMF = BLV
EMF = -(N*Δϕ)/Δt

Thank you for your time.

2. Jun 22, 2014

### rude man

Because the rate of change of the magnetic flux is maximum when the coil is 'horizontal'. The flux itself is zero but the rate of change of flux is maximum:
flux = BA sin(wt), coil is 'horizontal' at t=0 so flux(0) = 0
but d(flux)/dt = wBAcos(wt) which is maximum at t=0 so emf = wBA at t=0.