I put C for Question 9. It's definitely not A - it's a homopolar generator. It's not D either, it can't be AC as there's no change in the polarity - as the metal disc is always rotating in the same direction, relative to the static components (brushes/magnets/indicator). So that leaves B or C.
There's a picture on Page 5 of this thread with a diagram of a homopolar generator, and the accompanying post saying that it indicates the answer is B - might I point out, the orientation of the magnets in that picture is the opposite to whats in the exam paper.
syper said:
Also, Homopolar motors operate on a similar principle, as in, they don't need a commutator or slip rings etc, and yet operate on DC power. It's easy to make one too, and fun to mess around with
See:
http://en.wikipedia.org/wiki/Homopolar_motor
My answers:
1 C
2 B
3 D [Typo before]
4 B
5 D
6 A
7 B [wrong]
8 C [questionable - negative magnetic flux??]
9 C [as above]
10 B [no idea, probably wrong]
11 A
12 C
13 D
14 C
15 A