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please another short A2 synoptic edexcel question

please help me answer the last question in the paper.....
it's question 4c) ii) pleasssssssssssssssssssssssssse help me.

june 06 synoptic.pdf509.3KB

Reply 1

Mohit_C

Well the first thing you should know is that when a current is passed in the slinky, a mangetic field is created. As there is another small coil of wire inside, when there's a current in the slinky an emf is induced in this as there's a change in magnetic flux linkage.
Now when a compression pulse is sent along the slinky, the coils of wire get closer together hence increasing the magnetic flux that reaches the coil of wire (and decreases consequently due to the rarifractions). As the magnetic flux depends on the number of turns on the coil, an emf is induced then decreases. That is what the oscilloscope shows; the increase in voltage due to turns on coil closer together.