Question

A pendulum bob of mass of 80 mg and carrying a charge of 2 X 10- 8 C is at rest in a horizontal uniform electric field of 20,000 V/m. Find the tension in the thread of the pendulum and the angle it makes with the vertical.

Take( g = 9.8ms-2 )

Answer 1

Explanation:

Mass =80mg

Charge =2×10

−8

Coulomb

Electric field =20,000Vm

−1

Given, mass =80mg=8×10

−6

kg

charge =q=2×10

−8

C

Let T be the tension in string and θ is the angle if string with vertical.

In equilibrium

Tsinθ=qE⟶(1)

Tcosθ=mg⟶(2)

Divide (1) by (2) we get

tanθ=

mg

qE

⇒tanθ=

80×10

−6

×10

2×10

−8

×2×10

4

tanθ=0.5

θ=tan

−1

(0.5)

θ=27

0

Now,

tension, T=

sinθ

qE

=

sin27

0

2×10

−8

×2×10

4

=8.8×10

−4

V