The method and the results are on the electromagnetism lab. Do the analysis yourself first, then check the answers below.
Quick answer: Electromagnetism links electricity and magnetism: a current produces a magnetic field, a current-carrying wire in a field feels a force F = B I L, and a changing magnetic field induces a voltage. These answers go with the Physics 9-10 lab on electromagnetism: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
Model answers use the sample table. Your own values may differ by a few per cent, but the straight line through the origin and a gradient slightly below the ideal ratio of 2.0 are what a good set of results should show.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS2-5, GCSE P7
Question 1 Planning the readings
Changed: the primary voltage Vp. Measured: the secondary voltage Vs. Constant: the numbers of turns (200 and 400), the same iron core and the supply frequency.
Question 2 Predicted value
Vs = Vp × Ns ÷ Np = 6.0 × 400 ÷ 200 = 12.0 V. Measured 11.5 V. Difference = (12.0 − 11.5) ÷ 12.0 × 100 = 4.2 % below the prediction.
Question 3 Graph of Vs against Vp
The points lie on a straight line through the origin: Vs is proportional to Vp. Gradient = (19.0 − 3.8) ÷ (10.0 − 2.0) = 15.2 ÷ 8.0 = 1.90.
Question 4 Ratio for each row
Vs ÷ Vp = 1.90, 1.93, 1.92, 1.91 and 1.90. The mean is 1.91. The ideal value is 400 ÷ 200 = 2.00, so the difference is (2.00 − 1.91) ÷ 2.00 × 100 = 4.5 %.
Question 5 Why is Vs low?
Some energy is lost as heat in the resistance of the copper coils. Some field leaks out of the core so it does not pass through the secondary, and changing field in the iron induces eddy currents that warm the core. These losses lower Vs.
Question 6 Efficiency
Input power = 10.0 × 0.65 = 6.5 W. Output power = 19.0 × 0.30 = 5.7 W. Efficiency = 5.7 ÷ 6.5 × 100 = 88 %.
Question 7 Making it more reliable
Clamp the core tightly and use a laminated core so there is less leakage and fewer eddy currents; repeat each reading and take a mean, and use a thicker wire. These reduce energy losses and random error.
