Question

the time period of a pendulum various with length with its length is the length is increased how does the time period change

Answer 1

it changes as square of time period increases

Answer 2

time period of a pendulum is given by:
       t= 2 pie (square root    L/g  )
which means time period is directly proportional to square root of length.

As the length is increased 2 times, the time peiod is increased to square root 2 times.               OR
When lengh is increased 4 times, the time period doubles