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What typical voltages are induced from a typical magnet (50-75 gauss)

by drk52
Tags: induced voltage
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Apr30-12, 02:56 AM
P: 3
Hi, I'd like to use a millivoltmeter to research voltages induced from a basic ceramic magnet brushing by a conductor. So, I need to buy a millivolt meter. What voltage ranges will be required, and what read-rate should the millivolt meter have (in order for it to register the voltage in a split second brush with the magnet)? Is 1 millivolt a reasonable value to expect?
Any sources (books or online) you know I should check out related to this question?
Also, it would be nice if it would record these voltages (or at least leave it displayed so I could record them). Can you suggest any particular model millivolt meter?
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Apr30-12, 10:10 AM
P: 11,840
What is a "typical magnet"? Field strength is not even a parameter of the electromagnet itself.
Which type of experiment do you plan to perform?

Without these things, it is impossible to give any number.
Apr30-12, 02:00 PM
P: 349
If you just want to show that a moving magnet can produce an induced emf then you will need a sensitive milliammeter or micro-ammeter. I would suggest an analogue meter so that you can see movement of the pointer. A digital meter might be difficult to interpret.
If you have access to an oscilloscope that should also give some indication and you may be able to store the information.

Apr30-12, 08:17 PM
P: 3
What typical voltages are induced from a typical magnet (50-75 gauss)

Thanks for the reply truesearch... astute observation about the analog meter--probably right about that. And yes, I should probably be in the micro amp range to be sure to be sensitive enough. An oscillascope also would be great, but I do not have access to one, saving the data would also be ideal. Glad you were able to have a sense of what I was looking to find out. Thanks.
Apr30-12, 08:59 PM
P: 3
Thanks mfb for the reply,... by a typical magnet, I mean a permanent, ceramic magnet in the 50-75 gauss range, not an electro-magnet. The experiment I have in mind is to brush the permanent magnet across an insulated conductor (steel or copper) with different orientations of the permanent magnet in relation to the conductor (north-south direction oriented with the conductor--parallel or perpendicular), and record the various results.
I should probably use faraday's law to estimate the voltage, but I get confused when I try to appy it to this situation. I guess the number of turns would be 1. so you'd just have E = d(BA)/dt. B would be the magnetic field strengh, but A is the area? If the wire is straight where the magnet passes by, What area? Isn't the area usually the area of the coil? I guess it should have something to do with the distance of the magnet from the conductor--possibly. I guess B would go from 0 --> 50 gauss (is that the right units to use)? So, again, any help you can be regarding what range the voltmeter should be in, or possibly I should be observing the amps? And an appropriate (and cheap) model to use would be greatly appreciated.
Bob S
Apr30-12, 09:01 PM
P: 4,663
Let's try using Faraday's Law:
[tex] \oint E \space d \ell = V = -N \int n \cdot \frac{dB}{dt}dA [/tex]
N=100 turn coil
A=0.0005 meters2
dB=0.0075 Tesla
dt=0.1 seconds

V = 100 * 0.0005 * 0.0075 /0.1 = 3.75 millivolts

This is a very short pulse.

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