The method and the results are on the magnetic fields lab. Do the analysis yourself first, then check the answers below.
Quick answer: A magnetic field exerts a force on moving charges and on current-carrying wires. These answers go with the Physics 11-12 lab on magnetic fields: the graph, the calculations, the uncertainties and the conclusion explained, for all 6 analysis questions.
Here are the magnetic fields lab answers for physics grades 11-12: graph, calculations, uncertainties and conclusion. First do the lab yourself, then compare, and go back to the lesson if needed.
The sample data give a straight line through the origin, so the force is proportional to the current. The gradient divided by the wire length gives B. Your own data may differ, but should agree within the uncertainty of the balance.
Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB D.3
Magnetic fields lab answers: the analysis explained
Question 1 Plotting
F = Δm g: 0.17 g gives 1.7 × 10⁻³ N, up to 0.86 g giving 8.4 × 10⁻³ N. The five points lie close to a straight line through the origin, so F is proportional to I.
Question 2 Gradient
The best-fit line through the origin has gradient ΣIF/ΣI² = 3.4 × 10⁻³ N/A.
Question 3 Flux density
F = (BL) I, so B = gradient / L = 3.4 × 10⁻³ / 0.040 = 0.085 T, about 0.085 T.
Question 4 Direction
Reversing the current reverses the force on the wire. By Newton’s third law the force on the magnet reverses too, so the apparent mass change changes sign.
Question 5 Uncertainty
0.01 / 0.17 = 5.9 %, while 0.01 / 0.86 = 1.2 %. The smallest reading is therefore the least reliable; larger currents give a smaller percentage uncertainty.
Question 6 Improvement
Use a longer wire section or a stronger magnet to increase F; measure over a wider current range; use several turns of wire to multiply the force; measure L more precisely. Each raises F relative to the 0.01 g resolution.
