# FEM induced in a coil

Homework Statement:
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Relevant Equations:
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I need to find the FEM induced in a coil that rotates around the y axis and is inside a solenoid. The coil starts in the plane yz
##r## is the radius of the coil
##n## is the number of spiral by length of the solenoid.
##N## is the number of turns of the coil
##w## is the angular velocity that the coils rotate.
##I## is the current passing through the solenoid

I just thought this:
$$\phi = \langle B,A \rangle = \mu n I \pi r^2 N cos(\theta = wt)$$
$$\epsilon = -\dot \phi = \mu n I \pi r^2 N w sin(\theta = wt)$$

This is a simple exercise. But i can't see why my answer is wrong. That is, the answer provided by the list is ## \mu n I \pi r^2 N w cos(\theta = wt)##. The trignometric function is different. My answer says that at t=0 the induced FEM is zero, the other says it is maximum.

berkeman
Mentor
Sorry, what's FEM?

Delta2
Orodruin
Staff Emeritus
Homework Helper
Gold Member
Which axis is given as the solenoid’s symmetry axis? This is a vital piece of information. This is why you are asked to provide the homework statement verbatim, which you have ignored.

Sorry, what's FEM?
Based on context, I would assume the OP is not a native English speaker and the original language is a Latin language. FEM would really be EMF, electromotive force.

Delta2, rsk and berkeman
kuruman