14. A ball of 80mg mass and a 2*10-8 charge is hung with a thread in a uniform horizontal electric field of 2*104V/m. What is the angle made by the thread with vertical? a) 27 degree b) 30 degree c) 45 degree d) 0 degree
Answer: a Explanation: According to the diagram, Tsinθ = Eq; Tcosθ = mg. Where T is the tension in the thread, m is the mass of the ball, E is the electric field and q is the charge of the ball. Dividing these two, we get tanθ = Eqmg. Now substituting the value of E=2*104V/m, m=80mg, q=2*10-8C, g=9.8m/s2, we get tanθ = 2549. Therefore θ=27 degree.
