Question

The minimum surface density of charge on the plate, so that a body of mass 2 kg/m² may just be lifted, is
1. \(2.84 \times {10^{ - 5}}\;C/{m^2}\)
2. \(2.25 \times {10^{ - 5}}\;C/{m^2}\)
3. \(1.86 \times {10^{ - 5}}\;C/{m^2}\)
4. none of these

Answer 1

Correct Answer - Option 3 : \(1.86 \times {10^{ - 5}}\;C/{m^2}\)

Force per unit area \(= \frac{{{\sigma ^2}}}{{2{\epsilon_0}}} = mg\)

Then the surface density is given as \(\sigma = \sqrt {2{\epsilon_0}mg} = 1.86 \times {10^{ - 5}}\;C/{m^2}\).