# 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
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