25oC; α=1.85×10⁻⁵/oC
60oC; α=1.85×10⁻⁸/oC
30oC; α=1.85×10⁻⁷/oC
55oC; α=1.85×10⁻⁶/oC
The time period of a pendulum is given by, t = 2π√(l/g)
Δt = 2π√(g) * (Δl/2√l)
Δl = αΔθ
∴ Δt = π√(g/l) αΔT
∴ Δt₁/Δt₂ = ΔT₁/ΔT₂
∴ 12/4 = (40 - T)/(T - 20)
∴ 3T - 60 = 40 - T
∴ 4T = 100
∴ T = 25°C