Ncert Exercises & Solutions

Q 1.1) What is the force between two small charged spheres having charges of 2 × 10^–7C and 3 × 10^–7 C placed 30 cm apart in the air?

Repulsive force of magnitude = 6 x

10^{- 3}

N
Charge on the first sphere,

q_{1}

= 2 x

10^{- 7}

C
Charge on the second sphere,

q_{2}

= 3 x

10^{- 7}

CDistance between the spheres, r = 30 cm = 0.3 m

The electrostatic force between the spheres:

F = \frac{1}{4 π ε_{0}} \cdot \frac{q_{1} q_{2}}{r^{2}}

Where E = Permittivity of free space and

\frac{1}{4 π ε_{0}} = 9 \times 10^{9} N m^{2} C^{- 2}

Therefore, force

F = \frac{9 \times 10^{9} \times 2 \times 10^{- 7}}{(0.3)^{2}} = 6 \times 10^{- 3} N

Hence, the force between the two small charged spheres is 6 x

10^{- 3}

N. The charges are of the same nature. Hence, the force between them will be repulsive.