Numerical Problems
Q1

Calculate the Coulomb force between two protons separated at a distance of 1m. Calculate their gravitational attraction also.

Sol:
Charge of proton = + 1.6 × 10–19 C
Mass of proton = 1.66 × 10–27 kg
Coulomb force
where k = 9 × 109 N–m2/C2
Attractive force
Felec is a repulsive force and Fgrav is an attractive force.
But their ratios show how strong the Coulomb force
Q2

Calculate the Coulomb force between one proton and one electron separated at a distance of 1m. Compare their gravitational attraction also.

Sol:
Charge of proton = + 1.6 × 10–19 C
Mass of proton M = 1.66 × 10–27 kg
Charge of electron = – 1.6 × 10–19 C
Mass of electron = 9.11 × 10–31 kg
Repulsive force
where k = 9 × 109 N–m 2/C2
Calculation
Felec and Fgrav are attractive forces.
The ratios show how strong the Coulomb force is ∼ 1040 times stronger.