# M5 - Phy sics 7B WS M5(rev 2.0 Page 1 M-5 Faradays Law C E...

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Physics 7B WS M5 (rev. 2.0) Page 1 M-5. Faraday’s Law r E " d r s C # = \$ induced = % d B dt Questions for discussion 1 . In the figure below, there is a non-uniform magnetic field pointing into the page. a) If you move the metal loop to the right, will a current be induced in it? b) If so, will the induced current be clockwise or counter-clockwise? c) Suppose you want to move the loop to the left at constant speed. Will you have to exert any force to do this? Why or why not? d) Suppose instead that you want to move the loop upwards. Will a current be induced in it? Why or why not?

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Physics 7B WS M5 (rev. 2.0) Page 2 2 . The diagram below shows an infinitely long current-carrying wire, with two metal loops nearby. By means of a current generator (not shown), we cause the current in the wire to increase with time. a) Will a current be induced in loop 1? If so, will it be clockwise or counter-clockwise? b) Will a current be induced in loop 2? If so, will it be clockwise or counter-clockwise? 3. A crude current generator consists of a loop of wire with area A and resistance R. The loop is connected to a handle, so that someone can cause it to rotate within a uniform magnetic field B 0 that points upwards. a) How does this device generate current? b) Why will you have to do work in order to turn the handle?
Physics 7B WS M5 (rev. 2.0) Page 3 4 . Gauss’s Law for magnetism . " B = r B # d r A = 0 S \$\$ Consider the two vector fields shown below. a) Why can’t these be pictures of magnetic fields? b) For the field on the left, draw an imaginary closed surface for which Φ B 0. c) Do the same for the field on the right. 5. The left hand side of Faraday’s Law involves the induced emf, which is the line integral of the electric field around a closed loop. The right hand side involves the flux through a surface. The loop used on the left is the boundary of the surface from the right. However, the same loop can be the boundary for many different surfaces (Think of the film of soap on a bubble wand). Why does Gauss’

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M5 - Phy sics 7B WS M5(rev 2.0 Page 1 M-5 Faradays Law C E...

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