O-LevelPhysicsMagnetism5054/22 · May/June 2015 · Q66 Marks
Fig. 6.1 shows a simple a.c. generator. [Figure 6.1]
- (a)(i)Explain why an e.m.f. is induced,[2]
- (a)(ii)Explain why the e.m.f. is sometimes positive and sometimes negative.[1]
- (b)Changes are made to the a.c. generator, one at a time: • stronger magnets are used • more turns are wound on the coil • the coil is turned faster. Complete the table in Fig. 6.3 to show what happens to the maximum value of the e.m.f. and to the frequency of the alternating e.m.f. [Figure 6.3][3]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.
- [1] (a) (i) mention of (magnetic) field/flux (of N and S-poles)
- (coil/wire) cuts magnetic field/flux/lines
- [1] (a) (i) or magnetic flux in coil changes
- [1] (a) (ii) (one side of) coil cuts one way and then the other
- or (side) moves one way and then the other/returns
- or flux increases and then decreases
- [1] (b) increase in emf for both stronger magnets and more turns
- [1] (b) no change/same frequency for both stronger magnets and more turns
- [1] (b) increase and increase for turn the coil faster
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