Two identical conductors of copper and aluminium are placed in identical electric fields. The magnitude of induced charge in the aluminium will be

Assertion: $A$ metallic shield in the form of a hollow shell may be built to block an electric field.
Reason: In a hollow spherical shield,the electric field inside it is zero at every point.

Four very large metal plates are given the charges as shown in the figure. The middle two plates are then connected through a wire. Find the charge that will flow through the wire.

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.

$A$ conducting sphere of radius $10 \ cm$ is charged with $10 \ \mu C$. Another uncharged sphere of radius $20 \ cm$ is brought into contact with it and then separated. The ratio of the surface charge densities on the spheres will be ....... (in $: 1$)

If two conducting spheres are separately charged and then brought in contact,which of the following statements is true?