Question

Find the electric force between two protons separated by a distance of 1 fermi (1 fermi = 10⁻¹⁵ m). The protons in a nucleus remain at a separation of this order. 

Answer 1

We know:
Charge on a proton, q = 1.6 × 10⁻¹⁹ C
Given, separation between the charges, r = 10⁻¹⁵ m
By Coulomb's Law, electrostatic force,      

\[F = \frac{1}{4\pi \epsilon_0}\frac{q_1 q_2}{r^2}\] 

\[\Rightarrow F = 9 \times {10}^9 \times \frac{\left( 1 . 6 \times {10}^{- 19} \right)^2}{\left( {10}^{- 15} \right)^2}\]
\[ \Rightarrow F = 230 N\]