Magnetic Induction: Exploring Voltage Peaks, Flux & Magnet Orientation

[ashleyrose03]

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?

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!

 

[mikelepore]

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?

 

[Moetasim]

I would like to provide a more detailed and accurate explanation for these questions. Firstly, the two voltage peaks observed in the experiment are due to the changing magnetic field as the bar magnet passes through the coil. When the magnet is dropped through the coil, the magnetic field lines are cut by the coil's turns, inducing a voltage in the coil according to Faraday's law of induction. As the magnet enters and exits the coil, the direction of the magnetic field changes, causing the induced voltage to have two peaks - one when the north pole of the magnet enters the coil and another when the south pole exits the coil. The peak when the south pole exits the coil is typically higher due to the stronger magnetic field of the south pole compared to the north pole.

The effect of changing height on the induced voltage is related to the rate of change of the magnetic flux. As the height of the magnet above the coil increases, the time taken for the magnet to pass through the coil also increases, resulting in a slower rate of change of the magnetic flux. This leads to a decrease in the induced voltage. On the other hand, when the height is decreased, the rate of change of the flux increases, resulting in a higher induced voltage.

The greatest change in flux per unit time occurs when the magnet is passing through the coil at a constant speed. This is because the magnetic field lines are being cut by the coil at a constant rate, leading to a constant change in flux per unit time. When the magnet is stationary, there is no change in the magnetic flux and therefore no induced voltage.

When the magnet is dropped upside down, the magnetic field lines are still being cut by the coil, but in the opposite direction. This results in a change in the direction of the induced voltage, but the magnitude of the voltage remains the same.

In summary, the voltage peaks observed in the experiment are due to the changing magnetic field as the magnet passes through the coil. The height of the magnet affects the rate of change of the magnetic flux, resulting in a higher or lower induced voltage. The greatest change in flux per unit time occurs when the magnet is passing through the coil at a constant speed. And when the magnet is dropped upside down, the direction of the induced voltage changes, but the magnitude remains the same.