PS09-1MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of Physics 8.02 Spring 2010 Problem Set 9 Solutions Problem 1: Short Questions (a) When a small magnet is moved toward a solenoid, an emf is induced in the coil. However, if the magnet is moved around inside a toroid, no measurable emf is induced. Explain. Moving a magnet inside the hole of the doughnut-shaped toroid will not change the magnetic flux through any turn of wire in the toroid, and thus not induce any current. (b) A piece of aluminum is dropped vertically downward between the poles of an electromagnet. Does the magnetic field affect the velocity of the aluminum? Explain. Yes. The induced eddy currents on the surface of the aluminum will slow the descent of the aluminum. It may fall very slowly. (c) What happens to the generated current when the rotational speed of a generator coil is increased? The maximum induced emf will increase, increasing the terminal voltage of the generator resulting in a larger amplitude for the current. (d) If you pull a loop through a non-uniform magnetic field that is perpendicular to the plane of the loop which way does the induced force on the loop act? The direction of the induced force is opposite the direction of the pulling force.
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