A thermometer initially at a steady temperature of 30°C is inserted in a water bath maintained at 90°C. The initial rate of temperature rise of the thermometer is 2°C/s. Assuming first order behavior, the thermometer reading (in °C) after one minute is ______ (rounded off to one decimal place).

Question

Accepted Answer

The correct answer is 81 to 83. GATE 2026 official key: 81.0 to 83.0. dT/dt|0 = (90−30)/τ = 2 gives τ = 30 s. T(t) = 90 − 60e^(−t/30). At t = 60 s: T = 90 − 60e⁻² ≈ 81.9°C.