what will the effect on the value of time period of simple pendulum in an elevator?

Answer 1

to put it another way, the net gain/loss will be zero for a round trip. for example the pendulum clock will always have precisely the right time at the gound floor after returning from each trip. the pendulum responds to both gravitational and accelleration forces, so the period changes slightly as the elevator runs up and down. fyi the same affects happen when transported in trucks going around curves, which is why the pendulum is normally shipped disconnected.

Answer 2

If the elevator is accelerating upward, the apparent force of gravity increases. This increases the "spring constant" of the force, speeding up the pendulum. Downward acceleration causes a slowing.