The method and the results are on the transformers lab. Do the analysis yourself first, then check the answers below.
Quick answer: An alternating current reverses direction regularly, and its rms value, V₀/√2 for a sine wave, gives the equivalent steady heating effect. These answers go with the Physics 11-12 lab on transformers: the graph, the calculations, the uncertainties and the conclusion explained, for all 6 analysis questions.
Here are the transformers 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 show Vs proportional to Ns, with a gradient slightly below the ideal value because of losses. Your readings will differ, but they should again be directly proportional to the number of secondary turns.
Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: A Level 3.7.5
The four points lie on a straight line through the origin, so Vs is proportional to Ns.
Question 2 Gradient
gradient = ΣNV/ΣN² = 0.0232 V per turn (23.2 mV per turn).
Question 3 Ideal gradient
Ideal gradient = Vp/Np = 6.0 / 240 = 0.0250 V per turn. The measured gradient is 93 % of this.
Question 4 Energy losses
Flux leakage (not all flux from the primary links the secondary), eddy currents in the core and resistance of the coils. Each makes the secondary emf smaller than predicted.
Question 5 Why ac?
A dc supply gives a constant flux, so ΔΦ/Δt = 0 and the secondary voltage is zero apart from a brief pulse at switch-on.
Question 6 Uncertainty
0.1 / 1.4 = 7 %, the largest uncertainty. Use a higher input voltage, or a voltmeter with finer resolution, to make readings larger.
