# Magnetic Induction

1. In lab, we used a 400-turn coil test apparatus, mounted on an adjustable stand so a bar magnet could be dropped through it from different distances above it. In addition to the apparatus, we also used a voltage sensor and the Pasco interface used to display a graph of the induced voltage on the computer screen.

2. Why are there 2 voltage peaks? Which peak is higher and why? What is the effect of changing height? When does the greatest change of the flux per unit time occur? What happens when the magnet is dropped upside down?

3. The Attempt at a Solution
For the first question - why are there 2 voltage peaks - I think it is because of the north and south ends of the magnet, but I haven't been able to develop a more substantial answer. For the second question, I think the end that goes in last will be higher, but I'm not sure why. For the third question, I said that voltage changes - as height increases, voltage decreases. For the fourth question, I said the greatest change in flux occurs when each end is going through, but I don't think this makes any sense. And, for the last question, I said that the magnetic fields switch, but again am unsure of this answer.

Thanks for any input!

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## Answers and Replies

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Think of the imaginary lines of the magnetic field, coming out of the north pole of the magnet, and going into the south pole. Visualize those lines crossing the surface area of the coil. It's not important how many lines cross that area, but what's important is the rate of change of the number of lines that cross that area. So you want to picture the moments when the number of lines crossing that area is increasing, decreasing, having a minimum, having a maximum. For example, is there a point in time when that rate reaches a minimum for an instant?