Q172 · Practice questionComplex familiar5 marks
QUESTION 172 (5 marks)
A coil has turns, each of area , in a uniform field. The coil rotates so its area normal changes from parallel to the field to to the field in .
a)[2 marks]
Calculate the initial and final magnetic flux per turn.
b)[3 marks]
Calculate the magnitude of the average induced EMF. Would this equal the peak instantaneous EMF? Explain.
WORKED SOLUTION
5 marksPractice marking scheme
ANSWER
(a) ; . (b) Magnitude of the average EMF ; the peak cannot be obtained from the endpoint data alone.
Worked solution
(a) , where is measured from the area normal. Initially , so . Finally .
(b) . The instantaneous EMF depends on the instantaneous rate of flux change, which the endpoint angles and elapsed time do not specify.
Equivalent physically justified methods and consistent equivalent units accepted.
Displayed decimals are model answers; accept appropriate significant figures and consistent rounding from stated constants.
Part a: Calculate initial flux with normal parallel to B.
Part a: Calculate final flux using the angle to the normal.
Part b: Apply Faraday law to the flux change per turn.
Part b: Calculate the average EMF.
Part b: Distinguish average rate from an unspecified peak rate.
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