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Testing blocks with a permanent magnet
Figure 3 shows three metal blocks. The blocks are not labelled. One block is a permanent magnet, one is iron and one is aluminium.
Describe how another permanent magnet can be used to identify the blocks.
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Marking points
- 1 Say that the aluminium block will not be affected by the permanent magnet.
- 2 Say that the iron block will be attracted to the permanent magnet.
- 3 Say that the permanent magnet block can be identified because it can be repelled by the other permanent magnet.
Full-mark answer
Bring another permanent magnet near each block. The aluminium block will have no effect. The iron block will be attracted to the permanent magnet. The block that can be repelled is the permanent magnet.
Why this answer loses marks
The permanent magnet attracts the iron and the permanent magnet, so those two can be identified.
Attraction alone cannot distinguish iron from a permanent magnet; repulsion is needed to identify the permanent magnet.