Download Magnetic Fields

Magnetic Fields
1. Two protons are traveling parallel to each other in the same direction and at the same speed.
A. The electric force between them is...
B. The magnetic force between them is...
1. Attractive
1. Attractive
2. Repulsive
2. Repulsive
3. Zero
3. Zero
C. The net force between them is …
1. Attractive
2. Repulsive
3. Zero
2. The long straight wire picture below carries a current I = 12 A along the x axis.
A. What is the magnetic field (magnitude and direction ) at the point (0, 0.2) m due to just a 1 mm
long segment of the wire centered on the origin?
B. What is the magnetic field (magnitude and direction) at the point (0, 0.2) m due to a 1 mm
segment of the wire centered at x = -0.2 m?
P y = 0.2 m
.
x = -0.2m
0
I = 12 A
3. Two long, straight, horizontal conductors carry equal, but opposite currents. The two wires are
stacked vertically separated by 1.0 cm.
A. What is the magnitude of the current such that the magnitude of the magnetic field half way
between them is equal in magnitude to the horizontal component of the earth’s magnetic field
(17 µT in Platteville)?
B. What is the orientation of the currents (top current running N,S,E, or W) such that the field at
the midpoint exactly cancels the earth’s horizontal component?
6. Examine the current-carrying wire in the figure below. The current is coming out of the page. We
are interested in the field a distance r away.
A. Do the line integral ∫B ∙ dl by integrating CCW around the circular path at
radius r (dotted line in the figure at right). [Hints: Are B and dl parallel
everywhere along the circle? Does B depend on where we are on the circle?
What is the distance we are actually integrating around?]
B. You have just written Ampere's Law, which says that the line integral ∫B ∙ dl is
equal to μ0Ienclosed. But if the circle we integrated around did not have the wire
directly at its center, and was instead offset, as in the following diagram.
Explain whether or not the integral will still be equal to μ0Ienclosed or if it will be
more complicated, and why.
r
r
7. An Amperian loop is drawn around two current carrying wires, as shown below. What is the value of
∫B ∙ dl moving CCW , viewed from above, around the loop? (Note that I1 and I2 don’t have to be the
same size.)
i2
i1
A. μ0i1
B. μ0i1
C. μ0(i1 + i2)
D. μ0(i1 - i2)
E. Zero