Question

Consider a coin of Example 1.20. It is electrically neutral and contains equal amounts of positive and negative charge of magnitude 34.8 kC. Suppose that these equal charges were concentrated in two point charges seperated by (i) 1 cm `(∼ 1/2 xx "diagonal of the one paisa coin")`, (ii) 100 m (~ length of a long 6 building) and (iii) 10⁶ m (radius of the earth). Find the force on each such point charge in each of the three cases. What do you conclude from these results?

Answer 1

1. `F_1 = |q|^2/(4pi ε_0 r_1^2) = (8.99 xx 10^9  (Nm^2)/C^2) ((3.48 xx 10^4 C))/(10^-4 m^2)` = 1.1 × 10²³ N
2. `F_2/F_1 = r_1^2/r_2^2 = (10^-2  m)^2/(10^2 m)^2` = 10^–8 ⇒ F₂ = F₁ × 10^–8 = 1.1 × 10¹⁵ N
3. `F_3/F_1 = r_1^2/r_3^2 = (10^-2 m)^2/(10^6 m)^2` = 10^–16

F₃ = 10^–16 F₁ = 1.1 × 10⁷ N.