# Homework Help: Charged particles deflecting in a statics question.

1. Oct 6, 2011

### davidmn

[SOLVED] Charged particles deflecting in a statics question.

1. The problem statement, all variables and given/known data

A particle mass 2g and carrying a charge of q is suspended from a light, insulating thread. A second particle carrying an equal and opposite charge is held near to the first particle in the same horizontal plane and causes it to deflect. When the particles are separated by 25cm it is observed that the thread makes an angle of 45° to the vertical. By considering the forces acting on the suspended particle, find the magnitude of q.

2. Relevant equations
F=Qq/(4∏ε r^2)
Trigonometry
Statics

3. The attempt at a solution
I've assumed that the 25cm is measured between the particles before the deflection.
I've drawn a force diagram and resolved the forces relative to the force from the stationary particle. So 2gsin(45) is acting downwards, tension in in the string acts in opposition to the electrostatic force and 2gcos(45). I am at a loss as to what is acting in opposite to the 2gsin(45). I can take a photo of what I have if anyone isn't clear on what I've done.

Last edited: Oct 6, 2011
2. Oct 6, 2011

### rude man

Your assumption does not correspond to the wording of the question.

Quote: "When the particles are separated by 25cm it is observed that the thread makes an angle of 45° to the vertical".

3. Oct 6, 2011

### davidmn

Ah. True. OK I have two answers now. They make sense, one for if g=9.81 and another for if g=the unit. Thank you very much.