A charged particle of mass 1.0 g is suspended through a silk thread of length 40 cm in a horizontal electric field of intensity 4.0×104NC−1 as shown in the figure. If the particle stays in equilibrium at a distance of 24 cm from the wall, find the net charge on the particle?
Let’s draw the free body diagram of the charged particle-
The situation is shown in figure. The forces acting on the particle are
(i) The electric force F = qE horizontally leftwards,
(ii) The force of gravity mg downward and
(iii) The tension T along the thread
As the particle is at rest, these forces should add to zero.
T cos θ = mg and T sin θ = F
or, F = mg tan θ
From the figure,
Thus, tan θ=34 From (i),