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Unit 2. Electricity and Magnetism
III. Magnetic field

Questions 1 and 2 refer to the path of an electron in a magnetic field B, shown below. No electric field is present. The electron's initial velocity is of magnitude v and along the + x direction. While in the field, the electron moves a distance l along the + x axis, and is deflected downward along the - y axis by a distance d.
1.With respect to the axes in the diagram, which of the following is the most likely direction of this magnetic field?
+ x
- z
+ z
- y
+ y
2.In terms of the quantities defined in the diagram and the fundamental charge e, How much work was done by the magnetic field in deflecting the electron from its straight-line path?
zero
evBl
evBd
½evBd
½evBl
Questions 3 and 4 refer to the image below
The rectangular wire loop of dimensions l by w, shown above, carries a current I in a uniform magnetic field B that points in the + y direction.

3.In which sense will the wire loop rotate?
About the y axis
About the z axis
About an axis in the yz plane, but neither the y nor z axis itself
About the x axis
About an axis in the xy plane, but neither the x nor y axis itself
4.In terms of the defined variables, what is the magnitude of the initial torque caused by the magnetic force?
IlB
2IlB
IlBw
2IlBw
½IlBw
5.A magnetic field points in the + x direction. An positron enters the field with velocity v, as shown in the diagram above. What direction of an applied electric field will cause the electron shown to move undeflected through the region of these fields?
+ y
+ z
- z
- y
+ y
6.A proton (of mass mp and charge e) enters a uniform magnetic field B and travels in a circular path of radius r, as shown in the diagram. In terms of given quantities and fundamental constants, how fast was the proton moving in its orbit?
7.Very long, fixed wire 1 carries current I1. Wire 2 carries current I2, and is suspended very close to and directly above wire 1 as shown in an overhead view in the diagram Wire 2 is free to move in any sense. Which of the following describes the motion of wire 2?
It will rotate, with the top of the wire deflecting to the right.
It will rotate, with the top of the wire deflecting to the left.
It will translate to the right.
It will translate to the left.
It will not move.
8.The north and south poles of a large magnet, producing a uniform 0.5 T field, are shown above. Ampere's law is applied using the closed path drawn on the diagram, traced clockwise. What contribution to is made by the segment XY?
-1.0 T·cm
+1.0 T·cm
-0.5 T·cm
+0.5 T·cm
zero
9.Two long wires carry antiparallel currents, as shown in the diagram above. The top wire carries 16 mA to the right, while the bottom wire carries 4 mA to the left. Regions I, II, and III are labeled in the diagram. Obviously the magnetic field an infinite distance from these wires will be zero. In which of the labeled regions will other zero(s) of the magnetic field occur?
Region I only
Region III only
Both regions I and III
Region II only
No other zeros of the magnetic field exist.
10.In an experiment, a constant current I is sent through a long straight wire. The magnitude of the magnetic field B is measured as a function of d, the perpendicular distance to the wire. The experimenter makes a graph with B on the vertical axis and (1/d) on the horizontal axis. What does the slope of the line on this graph represent?