CourseCourseConceptConceptDocsDocuments

AP Physics C: Electricity & Magnetism 12.2 Magnetism and Moving Charges Questions

Analyse how moving charges create magnetic fields and experience magnetic forces, including particle trajectories, crossed fields, energy, and experimental inference.

Syllabus
Effective Fall 2024
Course
AP Physics C: Electricity & Magnetism

Exam points

  • determine a moving charge's magnetic-field direction from charge sign, velocity, and observation geometry
  • predict how a moving charge's electric and magnetic fields vary with position and separation
  • determine magnetic-force direction and magnitude from q times v cross B
  • recognise conditions for zero force and use magnetic work to predict unchanged kinetic energy
  • derive and compare radii, periods, or projected motion for charged particles in uniform fields

Covered syllabus points

12.2.A—Describe the magnetic field produced by moving charged objects12.2.B—Describe the force exerted on moving charged objects by a magnetic field

Question 1

[Maximum number: 1]

Two small spheres have equal and opposite charges and are travelling parallel to each other with speed v to the right, as shown above. What is the direction of the magnetic field midway between the spheres at the instant shown?

A

Out of the page

B

Into the page

C

Toward the bottom of the page

D

Toward the top of the page

E

Undefined, since the magnitude of the magnetic field is zero.

Figure for Question 1 — AP Physics C: Electricity & Magnetism

Question 2

[Maximum number: 5]

Long, parallel wires S and T are a distance 2 d apart. Both wires carry equal currents I, but the currents are in opposite directions. Both wires are parallel to the x-axis. At the instant shown in Figure 1, Sphere 1 is a distance d above Wire S, Sphere 2 is a distance d below Wire S, and both spheres are moving with speed v in the +x-direction. Each sphere has positive charge +Q.

Gravitational effects are negligible.

Figure 1

Figure 1

Question (a)

(a)

F1F_{1} is the magnitude of the magnetic force exerted on Sphere 1 due to the currents in wires S and T. F2F_{2} is the magnitude of the magnetic force exerted on Sphere 2 due to the currents in wires S and T.

Indicate whether F2F_{2} is greater than, less than, or equal to F1F_{1} by writing one of the following.

- F2>F1F_{2}>F_{1}

- F2<F1F_{2}<F_{1}

- F2=F1F_{2}=F_{1} Justify your answer.

[ 3 ]

Question (b)

(b)

Later, Wire T carries current 3 I in the +x-direction. At the instant shown in Figure 2, Sphere 2 is a distance d below Wire S and is moving with speed v in the +x-direction. Fnew F_{\text {new }} is the new magnitude of the magnetic force exerted on Sphere 2 due to the currents in wires S and T.

Figure 2

Figure 2

Indicate whether Fnew F_{\text {new }} is greater than, less than, or equal to F2F_{2} by writing one of the following.

- Fnew >F2F_{\text {new }}>F_{2}

- Fnew <F2F_{\text {new }}<F_{2}

- Fnew =F2F_{\text {new }}=F_{2} Briefly justify your answer by referencing your derivation in part B.

[ 2 ]
All question bank results loaded