At a green light, you pass over top of the in-pavement wire loop that triggers t

Question

At a green light, you pass over top of the in-pavement wire loop that triggers the red-light / speed camera.

Let's say you're going 50 km/hr, which is the speed limit there.

Let's estimate that, under these conditions, the magnetic parts of your car change the magnetic flux through the loop from 0 nT m2 to 20,000 nT m2 when you drive over the loop, in a time of 0.02 seconds.

These numbers are only the flux due to your car - the earth's field also has a flux there but it is virtually constant. The loop has three turns. What is the magnitude of emf produced in the loop?

Explanation / Answer

= -d/dt

= 3 * (20000*10^-9) / 0.02

= 3*10^-3 V

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