Chapters 28 (021)
Q20 An electron enters a region of uniform electric
and magnetic fields. It is observed that the velocity
of the electron is unaffected. A possible
explanation is that the velocity is:
A1 perpendicular to both E and B
A2 parallel to B
A3 parallel to E and has magnitude
E/B
A4 perpendicular to E and parallel
to B
A5 perpendicular to B and parallel
to E
Q21 A loop of wire carrying a current of 2.0 A is in
the shape of a right-angle triangle with two equal
sides, each 15 cm long. A 0.70-T uniform magnetic
field is in the plane of the triangle and is directed as
shown in figure 7.
The magnetic force on side 3 is:
A1
A2
A3
A4
A5
0.21 N, into of the page
0.21 N, out the page
0.30 N, out of the page
0.30 N, into the page
zero
Q22 A closed loop has an area of 5.8*10**(-2)
m**2 and carries a current of 3.0 A. It is placed in
an external magnetic field ,whose magnitude is
0.50 T, with its dipole moment initially making an
angle of 90 degrees with the external magnetic
field. How much work is done by the magnetic
field as it rotates the loop from its initial orientation
to the final orientation where the dipole moment is
aligned with the field?
A1
A2
A3
A4
A5
+ 0.087 J
- 0.087 J
+ 0.042 J
- 0.042 J
zero
Q23 A charged particle has a speed of 2.03*10**5
m/s, and is circulating in a plane perpendicular to a
uniform magnetic field. If the frequency of circling
is 100 kHz, then the radius of the circle is:
A1
A2
A3
A4
A5
0.322 m
1.11 m
0.915 m
0.852 m
0.753 m
S-29-2
An electron moving along the positive x-axis
perpendicular to a magnetic field experiences a magnetic
deflection in the negative y-direction. What is the
direction of the magnetic field?
S-29-12
A wire, 40 cm long, carries a current of 20 A. It is bent
into a loop and placed with its plane perpendicular to a
magnetic field (B = 0.52 T). What is the torque on the
loop if it is bent into an equilateral triangle, a square or a
circle?
S-29-14
A conductor suspended by two flexible wires (as in the
figure) has a mass per unit length of 0.040 kg/m. What
current must exist in the conductor in order for the
tension in the supporting wires to be zero? Assume B =
3.6 T directed into the page. What is the required
direction for the current?
S-29-28
The magnetic field of the Earth at a certain location is
directed vertically downward and has a magnitude of 0.5
gauss. A proton is moving horizontally toward the west
in this field with a speed of 6.2 106 m/s. What are the
direction and magnitude of the magnetic force the field
exerts on this charge? What is the radius of the circular
arc followed by this proton?
S-29-9
A proton moves with a velocity v = (2i – 4j + k) m/s in a
region in which the magnetic field is B = i + 2j – 3k T.
What is the magnitude of the magnetic force this charge
experiences?
S-29-29
A singly charged positive ion has a mass of 3.20 10-26 kg.
After being accelerated from rest through a potential
difference of 833 V, the ion enters a magnetic field of
0.920 T along a direction perpendicular to the direction
of the electric field. Calculate the radius of the ion in the
field.