Exam 20: Magnetic Fields and Forces

A proton with initial kinetic energy E is moving in circular motion in a uniform magnetic field. When it has completed one fourth of a revolution, what is its kinetic energy?

A proton moves across the Earth's equator in a northwesterly direction. At this point the Earth's magnetic field has a direction due north and is parallel to the surface. What is the direction of the force acting on the proton at this instant?

Electrical charges and magnetic poles have many similarities, but one difference is:

A proton and an alpha particle are moving perpendicular to a uniform magnetic field with the same speeds. If the velocity of the proton is at an angle of 20° with respect to the magnetic field direction, at what angle to the magnetic field direction would the alpha particle be moving if it experiences the same magnitude magnetic force as the proton? The alpha particle has 4 times the mass of the proton and twice its charge.

If a charged particle is moving in a uniform magnetic field, its path can be:

A wire is lying horizontally in the north-south direction and the horizontal magnetic field is toward the east. Some positive charges in the wire move south and an equal number of negative charges move north. The direction of the force on the wire will be:

Four long wires are perpendicular to the x-y plane. Each wire carries the same magnitude current. Wire 1 goes through point (a, a, 0) on the x-y plane, wire 2 goes through the point (-a, a, 0), wire 3 goes through the point (-a, -a, 0), and wire 4 goes through the point (a, -a, 0). Wires 1 and 3 carry their currents in the positive z direction and wires 2 and 4 carry their currents in the -z direction. What is the direction of the resulting magnetic field at the origin?

An electron is moving at a speed of 12 *10⁶ m/s at an angle of 30° with respect to a uniform magnetic field of 8.0 * 10^-4 T. What is the radius of the resulting helical path? (m_e = 9.11 * 10^-31 kg, q_e = 1.6 *10^-19 C)

A proton, which moves perpendicular to a magnetic field of 0.60 T in a circular path of radius 0.080 m, has what speed? (q_p = 1.6 *10^-19 C and m_p = 1.67 *10^-27 kg)

An electron which moves with a speed of 7.5 *10³ m/s parallel to a uniform magnetic field of 0.40 T experiences a force of what magnitude? (e = 1.6 *10^-19 C)

Two long parallel wires 15 cm apart carry currents of 5.0 A and 8.0 A in the same direction. Is there any point between the two wires where the magnetic field is zero?

Magnetic reversals of the Earth's field have occurred on the average every 200,000 years over the past 5 million years. When was the last magnetic reversal?

The current in a long wire creates a magnetic field in the region around the wire. How is the strength of the field at distance r from the wire's center related to the magnitude of the field?

The force on a charged particle created by its motion in a magnetic field is maximum at what angle between the particle velocity and field?

A current in a solenoid coil creates a magnetic field inside that coil. The field strength is directly proportional to:

Magnetic blood flow meters function using which of the following?

Two parallel wires are separated by 0.25 m. Wire A carries 4.1 A and Wire B carries 10 A, both currents in the same direction. The magnetic permeability in empty space µ₀ = 4 $\pi$ * 10 ^{- 7} T.m/A. The magnitude of the force on 1.4 m of Wire A is:

Two parallel conductors each of 0.50-m length, separated by 5.0 *10 ^{- 3} m and carrying 3.0 A in the same direction, will experience what type and magnitude of mutual force? (magnetic permeability in empty space µ₀ = 4 $\pi$ *10 ^{- 7} T.m/A)

A charged particle moving perpendicular to a magnetic field has a magnet force on it. But when an observer moves with the particle, so that the particle has a relative velocity of zero with respect to the observer, one would expect there would be no magnetic force. Yet there is still a force. If it is not a magnetic force, then what is the source of this force?

Solenoid #1 has a length L, cross-sectional area A, and N turns. Solenoid #2 has a length 2L, cross-sectional area 2A, and 2N turns. Which long solenoid has the greater magnetic field at its center when equal currents are going through them?