Question

The earth has a net electric charge that causes a field at points near its surface. The charge on the earth is supposed to be a result of an atmospheric battery created between ionosphere and the earth. The electric field near the earth's surface is believed to be $150N{C}^{-1}$ and directed towards the centre of the earth. A man suggested that this electric field may be used in flying. What magnitude and sign of charge would a $60kg$ human have to acquire to overcome his or her weight?

• A. $6C$
• B. $4C$
• C. $-6C$
• D. $-4C$
• E. None

Answer 1

The correct option is D $-4C$

In order to overcome his or her weight, the electrostatic force must balance his or her weight i.e., $qE=mg$
$\Rightarrow q=\frac{mg}{E}=\frac{60\times 10}{150}=4C$
As the electric field is directed towards the earth's center, so the sign of charge should be negative. Thus, $q=-4C$