# Earth's Magnetic Field Experiment / Helmholtz Coils?

1. Oct 3, 2012

1. The problem statement, all variables and given/known data
In my ab, we were supposed to obtain the horizontal component of the earth's magnetic field by measuring the period of oscillation of a bar magnet in a known field using the Helmholtz coils, a resistor, and an AC power amplifier. Now during this experiment I had issues with the measuring the period. The reason for so, is because my period of oscillation when applying 1 voltage to the coils would be higher than no applied voltage. And yet when I apply 2, 3, 4, or 5 voltages to the initial 0 applied voltage of the Helmholtz coils, the period of oscillation would decrease (like it's supposed to).
Therefore, my question is:
Why is it when I apply 1 voltage to the Helmholtz coils the oscillation slows down, but when I apply additional voltage to that, the oscillation will speed up?

2. Relevant equations

3. The attempt at a solution
I don't understand why it would slow down only when I add the 1 voltage, and not when I add the additional voltages. Therefore, I would know I did something completely wrong. However, according to my Lab instructor I did everything correctly.

2. Oct 4, 2012

### M Quack

In a magnetic field coil, it is the current that matters, not the voltage.

Did you try negative currents/voltages?

Did you try to rotate the setup?

Have you estimated the magnetic field of your coils for the currents/voltages applied?

3. Oct 5, 2012

### rude man

How is the magnet suspended in the coil? How do you keep gravity from affecting the results? You need to describe the setup more fully.

4. Jan 17, 2013

### amiralles

hello i am new in this forum and would like to get some help,
Inside a helmoltz coil exist a magnetic field value due the earth magnetic field, that is without inducing any current to the coils,right?. Now if I want to induce a current in the coil to generate a specific magnetic field value,Does the resultant magnetic field is the sum of the two magnetic field values (magnetic field without current + magnetic field with current) or it is the specific magnetic field produced by the current only?.

5. Jan 17, 2013

### rude man

The magnetic field inside the coil is the (vector) sum of the Earth's field plus that induced by any current applied to the coil.