Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : The outer body of an aircraft is made of metal which protects persons sitting inside from lightning strikes.
Reason (R) : The electric field inside the cavity enclosed by a conductor is zero.
In the light of the above statements, choose the most appropriate answer from the options given below :

Solution

Physics sir · 4 steps

The metal skin of the plane is a Faraday cage: lightning charge stays outside, and the field inside is zero.

1. Check the reason. In electrostatic equilibrium the field inside the metal of a conductor is zero. Take a Gaussian surface inside the metal that surrounds the cavity. If the cavity holds no charge, Gauss's law and the zero field in the metal together give E⃗ = 0 everywhere inside the cavity. So (R) is correct.

   ∮ E⃗· dA⃗ = q_(enc)/ε₀ = 0 ⇒ E⃗_(cavity) = 0

2. Check the assertion. When lightning strikes, the charge spreads over the outer surface of the metal body and flows away along it. The cabin is the cavity, so the passengers feel no field from that charge. So (A) is correct.
3. Link them. The passengers are protected only because the field inside a conducting cavity is zero. This is electrostatic shielding, and it is exactly what (R) states.
4. So. Both statements are correct and (R) explains (A). The answer is (c).

The idea to keep. A closed conductor shields its hollow inside: any charge on it sits on the outer surface, and the field in an empty cavity is zero. Cars, aircraft and lifts work as Faraday cages for this reason.

Answer from the NTA final answer key. Solution by PrepWiser.