February 25, 2009
PHY 2054 Discussion Spring ‘09
Conceptual Review: Chapter 19
A . Magnetic Force & Field
1. A charged particle is moving in a uniform magnetic field. Under what condition is the force on the
particle maximum?
2. Explain right-hand rule #1.
B. Magnetic Force & Torque on current-carrying Conductors
1. A horizontal wire with mass m and length l carries current I and is in equilibrium without the force by
supporting wires. What is the minimum magnetic field?
2. Does the magnetic torque depend on the shape on a loop or position of rotational axis?
3. What are the net magnetic force and torque on the double loop in the figure?
D. Motion of Charges in Magnetic Fields
1. A charge is moving in a uniform magnetic field. If the velocity of a charge is increased, what happens
to the radius and period of the circular motion?
2. What velocity should a charged particle have to pass in a velocity selector undeflected?
E. Magnetic Field of Straight Wire and Circular Loop
1. Explain right-hand rule #2 and #3.
2. The magnetic field at P is zero. What is the current in the left wire?
3. Compare the magnetic field of 50 cm in radius, 100-turn closely wrapped loop with that of a 50-cm
long, 100-turn solenoid. They both carry a current of 1 A.
F. Magnetic Force between Two Parallel Wires
1. Compare the magnitude of the magnetic force on the left wire with that on the right wire in the Fig. 2.
2. Two parallel wires with one directly above the other carry equal currents. The top wire is in equilibrium.
If the currents in both wires are doubled, what happens to the distance between two wires?
February 25, 2009
PHY 2054 Discussion – Spring ‘09
Practice Exam Problems (Chapter 19)
1.
A stationary positive charge +Q is located in a magnetic field B, which is directed toward the right.
The direction of the magnetic force on Q is: (Magnetic Force) a. toward the right.
b. up.
c. down.
d.
There is no magnetic force.
2.
The magnetic pole of the Earth nearest the geographic North Pole corresponds to which of the
following? (Earth’s Magnetic Field)
a. a magnetic north pole
b. a magnetic south pole
c. a magnetic
arctic pole d. a magnetic antarctic pole
3.
A current-carrying wire of length 50 cm is positioned perpendicular to a uniform magnetic field. If
the current is 10.0 A and it is determined that there is a resultant force of 3.0 N on the wire due to the
interaction of the current and field, what is the magnetic field strength? (Magnetic Force on
Current-Carrying Conductors)
4.
a. 0.60 T b. 1.5 T c. 1.8 10-3 T d. 6.7 10-3 T
A circular loop carrying a current of 1.0 A is oriented in a magnetic field of 0.35 T. The loop has an
area of 0.24 m2 and is mounted on an axis, perpendicular to the magnetic field, which allows the loop to
rotate. What is the torque on the loop when its plane is oriented at a 25 angle to the field? (Magnetic
Torque)
5.
a. 4. 6 Nm b. 0.076 Nm c. 0.051 Nm d. 0.010 Nm
Two singly ionized isotopes, X and Y, of the same element move with the same speed perpendicular
to a uniform magnetic field. Isotope X follows a path of radius 3.35 cm while isotope Y moves along a
path 3.43 cm in radius. What is the ratio of the two isotope masses, mX/mY? (Motion of a Charge in a
Magnetic Field)
6.
a. 0.977
b. 1.02
c. 1.05
d. 0.954
Two long parallel wires 40 cm apart are carrying currents of 10 A and 20 A in the same direction.
What is the magnitude of the magnetic field halfway between the wires? (Magnetic Field of a Long,
Straight Wire)
7.
a. 1.0 × 10-5 T b. 2.0× 10-5 T
c. 3.0 × 10-5 T
d. 4.0 × 10-5 T
A solenoid with 500 turns, 0.10 m long, carrying a current of 4.0 A and with a radius of 10 2 m will
have what strength magnetic field at its center? (magnetic permeability in empty space µ0 = 4  107
Tm/A) (Magnetic Fields of Solenoids)
Answers: 1-d
2-b
3-a
4-b
5-a
a. 31 104 T b. 62 104 T c. 125 104 T d. 250 104 T
6-a
7-d