# Torque and frequency

1. Mar 26, 2014

### besnik93

1. The problem statement, all variables and given/known data
A simple model of a polar molecule is a rod of length L with mass m where the charges q
and -q is arranged at each end of the rod. The molecule is located between two capacitorplates where spacing is on potential difference between the capacitor is V. The molecule will have a
equilibrium position (apart from gravity), but when the molecule is rotated away from the angle θ
equilibrium position will be affected by a torque τ.

a) Calculate the torque τ. Calculate the frequency f at which the molecule can perform small oscillations around the equilibrium position

3. The attempt at a solution
I think of using the force on the charges which is the charge * electric field strength, but i dont know how to express that, can someone help please

2. Mar 26, 2014

### Rellek

If I am illustrating this correctly then this should have a couple moment applied to the "rod"?

The wording on this is a bit confusing, and if there a screenshot to go along with this, so we can all be on the same page?

3. Mar 26, 2014

### besnik93

I cant take a screenshot, but how to calculate a torque of these charges and this rod.

4. Mar 26, 2014

### Rellek

Well look at the force on your charges due to the magnetic field contained within the capacitor and recognize you'd have two equivalent moments directed in opposite directions at all times, which is a couple.

The equilibrium position is going to be at your center of mass of the rod it looks like.

5. Mar 26, 2014

### besnik93

How do i express that to make sense, i am really confused