University Physics-PHYS 221, Fall 2000, UT Martin

Quiz 7(Ch. 30), Nov. 6

Constants: permeability of free space, μ0=4π x 10 –7 Nm2/A2.

___1) What is the force on a 2 m section of an infinitely long wire that carries a 2 A current in east direction placed in a 0.1 T magnetic field along the north direction?

a) east        b) west             c) up(out of the ground)            d) down(into the ground)

___2) A straight wire with current I experiences a force F due to an external magnetic field as shown.  What is the direction of the magnetic field?

___3) Two wires are parallel and infinitely long and carry  2A and 4A currents respectively as shown.  What is the direction of the net magnetic field at a point halfway between the wires?

___4) Three infinitely long wires, equally spaced, carry 2A, 3A, and 4A currents respectively as shown.  The net force on 4A wire is in which direction?

___5) Two circular wires of radii 2 cm and 4 cm are concentrically placed in the xy plane.  The inner wire carries 4 A clockwise current.  What should be the current on the other wire if the magnetic field at the center is to be zero? DRAW a picure!

a) 4 A clockwise    b) 2 A counterclockwise           c) 8 counterclockwise

d) 0.125 A counterclockwise

___6) A semicircular wire of radius R carries a current I.   It sets up a 2 T magnetic field at its center.  If we increase its radius to 2R ( by adding more of the same wire to it), and decrease the current 4 times, the magnetic field at its center  is

a) 0.25 T          b) 16  T            c) 2 T           d) 4T

This text is for the two questions that follow:

Figure shows four arrangements in which long parallel wires carry equal currents directly into or out of the page at the corners of identical squares.

___7) Which configuration(s) sets up zero magnetic field at the center?

a) 1      b)2       c)3       d)4       e)1 or 2      f) 2 or 3      d) 3 or 4

____8) Which configuration(s) sets up the maximum net magnetic field at the center?

a) 1      b)2       c)3       d)4       e)1 or 2

9) A single coil wire with radius R carries a current I and sets up a 2 T magnetic field at its center.  If we make the same wire with the same current into a  two loop coil, what is the the magnetic field at the center?  SHOW YOUR WORK!