| Date | May 2011 | Marks available | 3 | Reference code | 11M.2.HL.TZ2.6 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Calculate, Determine, Explain, and Label | Question number | 6 | Adapted from | N/A |
Question
This question is about the emf induced in a coil.
Define magnetic flux.
A coil is rotated at constant speed in a region of uniform magnetic field.
The graph shows the variation with time t of the emf ε induced in the coil for one cycle of rotation.
(i) On the graph label, with the letter T, a time at which the flux linkage in the coil is a maximum.
(ii) Use the graph to determine the rate of change of flux at t=4.0ms. Explain your answer.
(iii) Calculate the root mean square value of the induced emf.
Markscheme
the product of (the magnitude of) the normal component of magnetic field strength;
and area through which it passes/with which it is associated;
or
φ = BA cos θ ;
all terms defined/shown on a diagram;
(i) letter T clearly marked at 5.0ms or 15ms;
(ii) 2.0V/Wbs-1;
emf equals rate of change of flux; {(clear statement or equation must be present to award this mark)
Use of slope to obtain answer is incorrect – this yields a value of 1.8.
(iii) 4.2V;
Examiners report
(i) Many candidates wrongly identified either 0 ms, 10 ms or 20 ms as the point at which the flux linkage was a maximum.
(ii) Those that had a clear understanding of the relationship between emf and rate of change of flux moved quickly and unambiguously to the correct answer. Those who did not understand the physics evaluated the gradient at 4.0 ms and failed to gain credit.
(iii) The calculation of rms induced emf was well done by the vast majority of candidates.
