A clock which keeps correct time at 20oC, is subjected to  40oC. If coefficient of linear expansion of the pendulum is 12×10−6/°C. How much will it gain or loose in time

Time period  T∝l⇒ΔTT=12Δll=12αΔθ Also according to thermal expansion  l'=(1+αΔθ)Δll=α+θ. Hence  ΔTT=12Δll=12αΔθ=12×12×10−6×(40−20)=12×10−5⇒ΔT=12×10−5×86400 seconds / day   ∴ΔT≈10.3 seconds / day