Question

give reasons for : pendulum clock goes slow in summer.

Answer 1

Due to seasonal change of temperature, the effective length of pendulum changes, due to which the clock goes fast in winter and slow in summer
In winter due to contraction, the effective length of the pendulum gets shortened so it's time period is decreased and the pendulum completes more oscillation in a given time that is the clock is very fast. But in summer because of expansion that is increase in the effective length of pendulum, its time period is increased and it completes less number of oscillation in a given time that is the clock is very slow