Question

Question 1.1: What is the force between two small charged spheres having charges of 2 × 10 −7 C and 3 × 10 −7 C placed 30 cm apart in air?

Class 12 - Physics - Electric Charges And Fields Electric Charges And Fields Page-46

Answer 1

According to Coulombs law,
F = KQ₁Q₂/r²
where , Q₁ and Q₂ are charges and r is the separation between charges .

Given, Q₁ = 2 × 10⁻⁷C
Q₂ = 3 × 10⁻⁷C
r = 30cm = 0.3 m
K = 9 × 10⁹ Nm²/C²
∴ F = 9 × 10⁹ × 2 × 10⁻⁷ × 3 × 10⁻⁷/(0.3)²
= 9 × 10⁹ × 6 × 10⁻¹⁴/0.09
= 6 × 10⁻³N

Hence, force = 6 × 10⁻³ N

Answer 2

Hey mate!

Here's your answer!!

Repulsive force of magnitude 6 × 10 - 3 N

Charge on the first sphere, q1 = 2 × 10 - 7 C

Charge on the second sphere, q2 = 3 × 10 - 7 C

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

Electrostatic force between the spheres is given by the relation,

$f \: = \frac{q1q2}{4\pi e0 \: {r}^{2} }$

Where, ∈0 = Permittivity of free space

1/4π£0 = 9 × 10^9 Nm²C^-2

F = 9 × 10^9 × 2 × 10^-7 × 3 × 10^-7/ (0.3)²= 6×10^-3.

Hence, force between the two small charged spheres is 6 × 10 - 3 N. The charges are of same nature. Hence, force between them will be repulsive.