We are given two statements:
Assertion (A): Work done to move a charge between two points is zero inside a uniformly charged shell.
Reason (R): Potential inside a uniformly charged shell is constant and equal to the potential at its surface.
Step 1: Verifying Assertion (A)
The work done to move a charge between two points is zero when the points lie within a region of constant potential.
According to Gauss's Law, the electric field inside a uniformly charged spherical shell is zero, meaning there is no force acting on the charge inside the shell.
Since there is no force, no work is done in moving the charge inside the shell.
Therefore, assertion (A) is correct.
Step 2: Verifying Reason (R)
The potential inside a uniformly charged spherical shell is constant and equal to the potential at its surface.
This is a consequence of the fact that the electric field inside a spherical shell is zero, and therefore, the potential inside must be uniform.
The potential inside the shell is the same as the potential on the surface of the shell.
Therefore, reason (R) is also correct.
Step 3: Relation between Assertion and Reason
Since both assertion (A) and reason (R) are correct and the reason explains the assertion, the correct option is (1).