20. Both conducting loops shown below are coplanar (in the y/z axes) and carry current as shown. They are separated by some arbitrary distance. Will they attract or repel each other? -о-о current Z current A. They will attract each other. B. They will repel each other. C. They will not exert a force on each other. D. They will attract each other and then repel each other as an oscillator.

13. You have the apparatus shown in Figure P21.13. A circular metal plate swings past the north pole of a permanent magnet. The metal consists of a series of rings of in- creasing radius. Indicate the direction of the current in one ring (a) as the metal swings down from the left into the magnet- ic field and (b) as the metal swings up to- ward the right out of the magnetic field. Use Lenz's law to justify your answers. Figure P21.13 Metal plate Magnet N

A negatively charged particle is moving with a constant velocity directed to the left through a region of a uniform magnetic field B directed into the page as shown in the figure, in which direction must an electric field be applied to keep the particle moving along a straight line? XB Select one: a.Upward b.Downward c.into the page d.To the leftin the plane of the page e.Out of the page 1.To the right in the plane of the page

Two long, straight wires are parallel and 5 cm apart. One carries a current of 2.0 A, the other a current of 5.0 A. If the two currents flow in opposite directions, what is the magnitude and direction of the force per unit length of one wire on the other?    a) 4.00e-5 N/m Away from each other b) 1.67e-5 N/m Towards each other c) 4.00e-5 N/m Towards each other d) 1.67e-5 N/m Away from each other