WBJEE 2026 Physics and Chemistry Paper

Concept:Newton's law of cooling governs the temperature change of the bars.Explanation:According to Newton's law of cooling, the rate of loss of heat is proportional to the excess temperature of the body over its surroundings.Since the two bars are identical and placed in the same surroundings, the constant $k$ in the cooling equation is the same for both.If the initial temperatures are $T_1$ and $T_2$, with $T_1 > T_2$, and the surrounding temperature is $T_0$, then the temperature at any time $t$ is given by:$$T(t) = T_0 + (T_{\text{initial}} - T_0)e^{-kt}$$The bar with the higher initial temperature always stays hotter than the other.It also cools more rapidly at the beginning, so its cooling curve has a steeper initial slope.As time passes, both temperatures approach $T_0$ asymptotically.Therefore, the correct figure should show two curves starting at different temperatures, the hotter one dropping faster, and both finally merging with the room-temperature line.Answer:Option B.