Quick answer: A moving charge or a current produces a magnetic field, and a magnetic field pushes sideways on other moving charges. This AP Physics 2 test on magnetic force has 8 questions worth 20 marks, to do in 45 minutes: field near a cable, direction of force and proton in a uniform field. The mark scheme is on a separate page; free printable PDF.
This test covers the field of a wire, the magnetic force on moving charges and wires, circular motion in a field and the force between parallel currents. It lasts 45 minutes and is worth 20 points. Use μ₀ = 4π × 10⁻⁷ T·m/A and e = 1.6 × 10⁻¹⁹ C.
Level: AP Physics 2 (algebra-based) · Curriculum: AP P2 Unit 12
Question 1 Field near a cable (2 marks)
A long straight cable carries 25 A.
- Calculate the magnetic field 4.0 cm from the cable. (1 mark)
- State the field at 8.0 cm when the current is doubled to 50 A. (1 mark)
Question 2 Direction of force (2 marks)
A proton moves north through a uniform field that points east.
- State the direction of the force on the proton. (1 mark)
- State the direction of the force on an electron with the same velocity. (1 mark)
Question 3 Proton in a uniform field (4 marks)
A proton moves at 1.2 × 10⁶ m/s at right angles to a field of 0.80 T.
- Calculate the magnetic force on the proton. (1 mark)
- Calculate the radius of its circular path. (2 marks)
- State the effect on the radius of doubling the speed. (1 mark)
Question 4 Force on a wire (3 marks)
A 0.80 m wire carries 6.0 A in a uniform field of 0.15 T.
- Calculate the force when the wire is at right angles to the field. (1 mark)
- Calculate the force when the angle is 40°. (1 mark)
- Explain why the force is zero when the wire is parallel to the field. (1 mark)
Question 5 Parallel wires (3 marks)
Two long parallel wires 3.0 cm apart carry 12 A and 8.0 A in the same direction.
- Calculate the force per metre of length. (2 marks)
- State whether the wires attract or repel. (1 mark)
Question 6 Work done (2 marks)
Explain why a magnetic field cannot change the speed of a charged particle. (2 marks)
Question 7 Sign of the charge (2 marks)
The diagram shows a particle moving to the right in a field directed out of the page. Its path curves upward.
Determine the sign of the charge and justify your answer. (2 marks)
Question 8 Undeflected beam (2 marks)
A beam passes undeflected through an electric field of 6.0 × 10³ V/m and a perpendicular magnetic field of 0.030 T.
- Calculate the speed of the particles. (1 mark)
- State what happens to a faster particle of the same charge. (1 mark)
