Quick answer: A magnetic field exerts a force on moving charges and on current-carrying wires. This Physics 11-12 test on magnetic fields has 8 questions worth 20 marks, to do in 45 minutes: defining the tesla, force on a rail wire and direction of a path. The mark scheme is on a separate page; free printable PDF.
This test covers magnetic force on wires and charges, circular orbits and velocity selectors. Show formulas, substitutions and units. Use e = 1.60 × 10⁻¹⁹ C and proton mass 1.67 × 10⁻²⁷ kg. Calculators are allowed.
Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB D.3
Question 2 Force on a rail wire (3 marks)
A 0.60 m metal bar carries 5.0 A at right angles to a field of 0.30 T.
- Calculate the force on the bar. (2 marks)
- State the force when the current is reduced to zero. (1 mark)
Question 3 Direction of a path (3 marks)
A positive ion enters a field that points out of the page, moving to the right as shown.
- Explain why the ion curves downwards. (2 marks)
- State what happens to its speed. (1 mark)
Question 4 Radius of a proton (3 marks)
A proton moves at 2.5 × 10⁶ m/s perpendicular to a 0.35 T field. Calculate the radius of its circular path.
Question 5 Why circular? (2 marks)
Explain why a charged particle moving perpendicular to a uniform magnetic field travels in a circle and not in a straight line.
Question 6 Velocity selector (3 marks)
Particles pass undeflected through crossed fields E = 6.0 × 10³ V/m and B = 0.025 T.
- Calculate their speed. (2 marks)
- State whether the answer depends on the particle’s charge. (1 mark)
Question 7 Comparing proton and electron (2 marks)
A proton and an electron enter a field at the same speed. State which has the larger orbit and explain why.
Question 8 Force on a wire at an angle (2 marks)
A 0.30 m wire carrying 8.0 A lies at 40° to a 0.15 T field. Calculate the force.
