# Homework Help: Hall Voltage Conundrum. Was Edwin Wrong?

1. Oct 14, 2011

### brogers62

First off, to answer my own question, I doubt it.

Secondly, a little background. While performing a basic experiment on the hall effect, I got some rather curious results.

The apparatus consists of a power source, an electromagnet, a gauss meter, a hall sensor, and a pair of multimeters to measure voltage and current.

So all is well. I have followed the given procedure, checked the connections and turned everything on. I begin gathering my data.

I was to measure the hall voltage from 0-50 mA at 5mA increments. The B field is 1500 Guass. (.15 tesla)

My results were to be expected, ranging from 0-20mA linearly.

Life is good.

Then I am asked to reverse the direction of the magnetic field. Easy, just switch the "+" and "-" connections of the coils. Now record again.

Same amp range, same increments. One problem. My data, which I have yet to look very closely at, is not a nice linear line. It increases until about 25 mA and then begins to decrease. By the time I reach 50 mA my Hall Voltage is on the other side of zero.

What the .......?????

I spoke with my professor, who is an incredibly competent experimental physicists, and he was puzzled. Something isn't right though.

Discuss

ps This happened very recently and will likely be address by the time I am back on campus next week but I figured "why not give you geniuses an opportunity to enlighten me?"

pss I am a novice at best so please keep the technical jargon to understandable levels.

psss This discussion will have no bearing on any grade I may or may not receive for my work on this lab.

pssss Thanks

2. Oct 15, 2011

### rude man

I would guess that your Hall sensor exhibits magnetic anisotropy for some reason. In other words, the B field is not symmetrical with the applied H excitation within the sensor. This could be due to quantum mechanical effects. A Hall sensor is typically not just a piece of isotropic metal or semiconductor as conveniently described in elementary physics texts.

A section of the following PhD thesis discusses various Hall effect devices and their respective characteristics: