Magnetic flux and emf through a rotating ring

[captainjack2000]

 

[captainjack2000]

Sorry I don't quite know how that happened!
Any way the question is
"A metal ring of radius R rotates with constant angular velocity about a diameter. Perpendicular to the rotation axis is a constant magnetic field B. Calculate as functions of time
a) magnetic flux through ring
b) emf induced

I know magnetic flux = BAcoswt
so emf = -magnetic flux/dt = ABwsinwt

 

[latentcorpse]

arent you missing a minus sign in your final answer?

 

[captainjack2000]

emf = -dphi/dt = -d/dt(BAcoswt) = -(-BAwsinwt) = ABwsinwt
i think
I am a bit confused by the fact that they say "about a diameter" how does this change things?

 

[latentcorpse]

ok. yeah my bad with the minus. the diameter bit just tells you the way its rotating its not rotating about the surface normal but rather like a dynamo would.