1) It is possible for a bolt of lightning to produce a damaging amount of electric current in an electrical appliance (particularly computers and other digital equipment) even when the lightning does not strike the appliance or the house in which it lives. Such digital circuits can often be damaged by voltages as low as 20 V. Because all circuit boards contain loops of wire or metal they interact with the lightning through Faraday’s Law. Explain how this might lead to damage of electronic equipment.

2) Robots are sometimes designed to follow wires embedded in factory floors. These wires carry steady (DC) currents. The robot carries a coil (many loops) of wire which it holds near the floor and to one side of the wire. As long as no current flows through the wire the robot knows that it is following the along the wire. If the robot turns away from the wire a current flows in the coil which notifies the robot of its error. How does this system work?

3) As an initiation rite you are required to place your hand (area = 0.016 square meters) in to a uniform 0.35 T magnetic field. What is the flux through your hand (ouch!) when the normal to your hand is parallel to the B field? When the normal is perpendicular?

4) A flexible wire is taken and wrapped into a single loop 4 cm in diameter. It is placed in a 0.55 T magnetic field so that the B field and the normal to the loop are parallel. You then take the ends of the wire and quickly pull them apart so the loop disappears in a time of 0.25 s (do a sketch or ask me if this doesn’t make sense to you). What is the magnitude of the EMF (voltage) produced between the ends of the wire?

5) The north pole of a magnet is moved away from a copper ring as shown. Which direction is the current flowing in the part of the ring furthest from you?

 

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6) The magnetic flux through a loop is given by the expression

2.

(the flux is in milliwebers or mT-m2) What is the magnitude of the induced voltage at t=2.0s? 

                          (31mV)

7) Two straight conducting rails form a right angle and are spanned by a conducting bar. The bar begins at the vertex of the rails and moves at a constant 5.2 m/s to the right. The B field points up out of the page and has a magnitude of 0.35 T. Determine an expression for the flux through the “loop” as a function of time. What is the induced voltage around the loop as a function of time?

3

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8) A rectangular loop of N turns, length a, and width b is rotating with period T in a constant magnetic field of mangitude B. Show that the induced voltage (EMF) is given by

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9) Using the previous result, design a loop which will generate 150 V when rotated in a field of 0.5 T. There are many solutions to this problem.