Coulomb’s law for electrostatic force between two point charges and Newton’s law for gravitational force between two stationary point masses, both have inverse-square dependence on the distance between the charges and masses respectively. (a) Compare the strength of these forces by determining the ratio of their magnitudes (i) for an electron and a proton and (ii) for two protons. (b) Estimate the accelerations of electron and proton due to the electrical force of their mutual attraction when they are 1 Å (= $10^{-10}$ m) apart? ($m_p$ = 1.67 × $10^{–27}$ kg, $m_e$ = 9.11 × $10^{–31}$ kg)

NCERT Example 1.3 Coulomb’s law for electrostatic force between two point charges and Newton’s law for gravitational force between two stationary point masses, both have inverse-square dependence on the distance between the charges and masses respectively. (a) Compare the strength of these forces by determining the ratio of their magnitudes (i) for an electron and a proton and (ii) for two protons. (b) Estimate the accelerations of electron and proton due to the electrical force of their mutual attraction when they are 1 Å (= $10^{-10}$ m) apart? ($m_p$ = 1.67 × $10^{–27}$ kg, $m_e$ = 9.11 × $10^{–31}$ kg)

If $10^9$ electrons move out of a body to another body every second, how much time is required to get a total charge of 1 C on the other body?

NCERT  Example 1.1 If $10^9$ electrons move out of a body to another body every second, how much time is required to get a total charge of 1 C on the other body? 

How much positive and negative charge is there in a cup of water?

NCERT Example 1.2 How much positive and negative charge is there in a cup of water?