Explain why you are safe and unaffected inside a car that is struck by lightning. Also explain why it might not be safe to step out of the car just after the lightning strike, with one foot in the car and one on the ground (Note that it is current that kills;, rather a small current passing through the region of the heart can be fatal.)

The electric current is the flow of charged particles per unit time through a cross section. The flow of charge is possible only because of difference in potentials of two positions.

The strike of lightning on car infuses a large voltage on the outer surface of car. The large voltage causes the movement of charged particle on the outer surface of charge but inside surface remains unaffected.

The charge affects only outer surface of car so the inside humans remains safe and unaffected.

The potential difference between two foots of human is called the step potential in any electric field. This potential difference is needed to flow of current in human body.

When anyone inside car exits immediately outside car after lightning strike on car with one foot inside car and other on the ground then due to the large difference in potential between car and ground a very large current will pass from human body that either harms or kills the human body.

Therefore, the inside person remains safe because all the charge due to lightning remains on the outer surface of car and immediate exit from car after lightning with one foot on car and other on the ground because it will cause large current through person and kills him.