CGPET 2018 Solved Paper

Given, mass, m=30.7×10−6kg
Charge, q=2×10−8C
Electric field, E=2×104V∕m
Let T is the tension in the string and θ is angle of string with vertical.
In equilibrium,
T‌sin‌θ=qE ........(i)
T‌cos‌θ=mg ........(ii)
From Eqs. (i) and (ii), we get
tan‌θ=

qE

mg

=

2×10−8×2×104

30.7×10−6×9.8

=1.329
⇒θ=tan−11.329
∴θ=53.05°
Hence, tension, T=

qE

sin‌θ

=

2×10−8×2×104

sin‌53.05°

=5×10−4N