|
||||||||||||
|
||||||||||||
|
||||||||||||
17 |
||||||||||||
An
electron has a mass of and a charge of . How fast must the electron be going for the
magnetic force to cancel the force of gravity if the magnetic field is
horizontal and has a strength of ? |
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
Solve for |
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
So Correct Answer is B ! |
||||||||||||
18 |
||||||||||||
A
wire is long and has a current of running in the wire due North. The wire is surrounded by an external
magnetic field with a field strength of which is directed due South. What is the magnitude of the magnetic force
the field is exerting on the wire? |
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
Since current is north and B field
is due south, the cross product is zero! |
||||||||||||
|
||||||||||||
|
||||||||||||
So Correct Answer is D ! |
||||||||||||
19 |
||||||||||||
|
||||||||||||
Two
wires are shown above. Wire 1 carries
a current straight out of the paper. The wire has a length of . Wire 2 carries a current going to the right. The wire has a length of . Wire 1 is located above wire 2 by a
distance of . What is the magnetic force that Wire 1
exerts on Wire 2. |
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
The B field for Wire 1 is concentric
circles going counter-clockwise as shown above. The magnetic force of wire 1 on wire 2 is
given by |
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
Since is parallel to , |
||||||||||||
|
||||||||||||
So
|
||||||||||||
|
||||||||||||
So the Correct Answer is C ! |
||||||||||||
20 |
||||||||||||
For
a magnet, the north pole is the pole where magnetic field lines exit the
magnet and the south pole is the pole where the magnetic field lines enter
the magnet. So where is the Earth’s
north magnetic pole currently located? |
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
The Earth’s north magnetic pole is
currently in the Southern Hemisphere. A
compass’s north pole of its needle, points north because the Earth’s south
magnetic pole currently lies in the Northern Hemisphere. The Earth’s magnetic poles do move
about. |
||||||||||||
|
||||||||||||
So Correct answer is B ! |
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
|
||||||||||||
|