Question: A high voltage dc power line falls on a car, so the entire metal body of the car is at a potential of with respect to the ground. What happens to the occupants (a) when they are sitting in the car and (b) when they step out of the car? Explain your reasoning.

The term electric potential is defined as the amount of work done by the unit charge in moving from one point to another against electric field.

The electric field obtained by the relation:

$\overrightarrow{E}=-\overrightarrow{\nabla }V$

Taking integration on side and taking limit from

$$\begin{gathered} {\int }_A^{B}dV=-\int Edr \\ {V}_B-V_A=-\int 0dr+C \\ {V}_B-V_A=C \\ {V}_B-V_A=C \end{gathered}$$

(a) There is no any charge flow between outer and inner metal surface of the car that’s why occupant out of danger when they are sitting in the car. This is because the charge flows out of the metal body of the car so that occupants are at the same potential.

Hence, the occupant is out of danger when they are sitting in the car.

(b) There is charge flow on the outer metal surface of the car body that’s why occupant in huge danger when they step out of the car. This is because the occupant will be in touch of the car and the ground while stepping out thus making a short circuit path.

Hence, the occupant in huge danger when they are step out of the car.