Help plz with a question about Faradays law?

Question

My question states use Faradays law to calculate the Emf induced in a ring when it is flipped through 180 degrees in 0.2s assuming that the flux changes uniformly during this time? ring diameter is 2.2cm, the magnetic field strength is 48uT acting 66 degrees below the horizon. I know that Faradays law is Emf = change in flux / change in time but thats as far as I have got, could somebody point me in the right direction Plz, many thanks in advance

Answer 1

I'd like to help you especially since I see you're getting no answers.  For me the difficulty is trying to understand what you mean by 48 micro Tesla "acting 66 degrees below the horizon".  Where is this horizon - you never mentioned it before and what's it have to do with the problem?  Edit your question with some explanation and maybe you'll get some help!!  Oh also - how can the flux change uniformly?

Answer 2

If the ring is horizontal to start with then the flux through it will be 48x10^-6 T x sin(66degrees).

When the ring is flipped over the flux will change from + the above value to - the value so the change in flux linkage will be twice the flux linkage: (think F -(-F) = F + F =2F)

change in flux linkage = 2x48x10^-6 x sin 66degrees

then the rate of change is 2x48x10^-6 x sin 66degrees/0.2s

This is the emf in volts.

Answer 3

I think you're on the right track to start. As the other contributor mentioned, hopefully there is a diagram, as the language is slightly ambiguous.

If you assume the ring is initially horizontal, then that initial plane is the "horizon".  Thus a vector 66 degrees below the horizon, is 24 degrees from the normal to the plane.

The initial flux normal through the ring is then 48 uT * cos(24 degrees) * pi * (0.011 m )^2.  The final flux is the same -- just negative  (actually, this would be cos(24+180) = -cos(24).

As the ring turns, the cos(theta) term is what gives rise to a changing flux -- basically the projected area of the ring is changing (or the component of the field perpendicular to the ring, depending on how you want to look at it).  In the in between angles you'd have to worry about some complicated geometry, especially since you are not told how the ring is turned -- but because you're told that the flux changes uniformly, I take this to mean that the derivative of flux with respect to time is constant -- meaning that you can calculate the slope just using the starting and ending flux values.

Answer 4

Hey there, IF the magnetic filed is 66 degrees below the horizon then what is the orientation of the ring relative to the horizon/magnetic field