# Homework Help: How would the magnetic field of a solenoid change if it used AC current

1. Oct 4, 2011

How would the magnetic field of a solenoid change if it used AC current instead of DC current? How would this affect the motion of a charged particle moving from the center to the side of the solenoid?

This isn't a homework problem, just something I'm curious about. Hence, there is no "right" answer, just probably some correct explanations.

If the wires of the solenoid had DC current flowing through them, the magnetic field would be constant, and the particle would move in a clockwise or counterclockwise motion. If the current were AC, I think the solenoid's magnetic field would change between B and -B with respect to time on a sine wave, where B is the field produced with the same amount of current with DC instead of AC. The force exerted on the charged particle would alternate between pushing it clockwise and counterclockwise so rapidly that I think it would jitter but continue to move in a relatively straight line.

Is this accurate? What other things could I consider? If a solenoid with AC current flowing through the wires has a magnetic field that flips direction very quickly, where could it be useful?

2. Oct 5, 2011

### 256bits

where could it be useful?

Well, maybe as a a buzzer. Or as a speaker. Or in a tool with a sharp hard metal point to etch glass.

3. Oct 5, 2011

How would an etching tool work? Would the alternating current cause the solenoid's magnetic field to fluctuate between positive and negative, to rapidly push and pull the sharp head?

4. Oct 5, 2011

### 256bits

That is how it would work.

Can you think of anything that uses a coil of wire as a solenoid.

What if you put a few of them in a row or a circle.