Positive charge Q is distributed uniformly over a circular ring of radius R.A particle with mass 'm' and a negative charge 'q' is placed on the axis at a distance 'x' from the centre.Find the force on the particle.Assuming x<<R, find the time period of oscillation of the particle if it is released from there.
Before I request for a solution, I would request someone to explain why the mass given here is relevant.
Secondly, can anyone please refer me a book/reference on electrostatics?I am fully comfortable with rigorous single variable calculus(I am in high school) and would not mind a book/reference that has really tough problems but explains the matter well.(My assessment is that I have not really understood the matter)
Edit:I can probably see that the x<<R condition is for approximation(or for some ignoring some quantity when it emerges in the answer or the steps leading to it)