The period of oscillation of pendulum clock change from day to night. Brass is used in the pendulum. temperature changes from ${ 35 }^{ 0 }C\quad to\quad { 20 }^{ 0 }C$ from day to night. In 12 hours the time that can be gained or lost is- (Coefficient of linear expansion for brass = $2\times { 10 }^{ -5 }/^{ 0 }{ C }$)