Question

Assertion: When a conductor is placed in an external electrostatic field, the net electric field inside the conductor becomes zero after a small instant of time.
Reason: It is not possible to set up an electric field inside a conductor.
A) Both Assertion and Reason are correct and reason is the correct explanation for Assertion;
B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C) Assertion is correct but Reason is incorrect.
D) Assertion is incorrect but reason is correct.

Answer 1

Hint: The electric field in simple terms is the electric force per unit charge exerted on a positive test charge. The direction of the electric field is taken as the direction of force which is applied by the electric field on a positive test charge.

Complete solution:
There are two types of electric field one is electrostatic field and another is electrodynamic field. The electrostatic field is a field that is static or stationary while the electrodynamic field is a field which is a dynamic or moving field. Here, the conductor is placed in an electrostatic field. If one places a charge inside the conductor then the charge will come outside on the surface of the conductor. The external electric field will move the free electrons which are already present inside the conductor to positive and negative polarities. The electric field will end at the extreme end of the negative charge and will again start at the extreme positive charge of the shell and hence there would be no electric field inside the shell. Therefore, the assertion is correct. Now, we have been given the reason that “it is not possible to set up an electric field inside the conductor”. It is not possible to set up an electric field inside the conductor because even when we pass a current through the conductor the charges inside the conductor will cancel out the external electric field as the charges inside the conductor will get polarized and after sometime forms an electric field inside the conductor which is of same magnitude and is opposite direction of the external electric field. In other words, they will cancel each other out and the net electric field inside the conductor is zero.

Final answer option A is correct. Both Assertion and Reason are correct and reason is the correct explanation for Assertion.

Note: Here, there would be no electric field inside the conductor but if we run current through an conductor then due to the moving charge on the surface of the conductor there would be a magnetic field induced around the conductor.