Acircular loop of radius 0.10 m is rotating in a uniform external magnetic field of 0.20 t. (a) find the magnetic flux through the loop due to the external field when the plane of the loop and the magnetic field vector are parallel.

Your answer is zero. :)

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Answer(a)   the matererials that are in contact, the two materials and the nature of their surfaces/// (b)/// the force pushing the two surfaces together, pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other