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Please see the images attached. Why does the emf graph have curves on it? What is causing the induced emf to change as it enters the magnetic field, and why is there a peak at 2.5 seconds and 7.5 seconds?

When my teacher drew a graph for a rectangular sheet of metal with the same movement as the coil (going in and then out of the magnetic field), his graph had straight lines (as shown below). Is my teacher wrong or is there a difference between a rectangular sheet of metal and a coil of wire? enter image description here

  • $\begingroup$ How is emf calculated? Do you expect to see the same emf waveform regardless of the shape of the coil? If not, why? $\endgroup$
    – Puk
    May 19, 2023 at 9:23

1 Answer 1


Is my teacher wrong


or is there a difference between a rectangular sheet of metal and a coil of wire?

Yes. The answer lies in the areas.

  • $\begingroup$ Thanks. Also, does it matter which way the curves go, or do you just need them to be on different sides of the x-axis? i.e. does putting a coil into a magnetic field always mean that positive emf is generated and taking it out always mean negative emf? $\endgroup$
    – cabbagesss
    May 20, 2023 at 7:52
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    $\begingroup$ Yes, it matters, but that depends upon choice of which direction of flow is taken as positive. Physics always must have some physical meaning for helping us get signs correct, and then some mathematical method to guarantee braindead use will also get them correct. $\endgroup$ May 20, 2023 at 8:14

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