Physics 4322 Homework Set 3 January 31, 2012 Due: Tuesday, February 7, 2012 1. A square loop of wire is placed in a magnetic field B as shown. The wire is released from rest and allowed to fall under the action of gravity. (a) Find an expression for the velocity v as function of time t . (b) How long a time is required to reach 90% of terminal velocity? (c) Describe the motion of the loop if a tiny section is removed so as to break the complete circuit. 2. A long solenoid with radius a and n turns per unit length carries a time-dependent current I ( t ) in the φ ^ direction. Find the electric field E at a distance s from the axis inside and outside the solenoid in the quasistatic approximation. 3. A square loop having side a and resistance R lies a distance s from an infinite straight wire that carries current I ( t ) = (1 – α t ) I for 0 ≤ t ≤ 1/ and 0 for all other times. (a) In what direction is the current in the square loop? (b) What total charge passes through a given point during the time the current exists? 4. Find the self-inductance per unit length of a long solenoid having radius
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