91Ó°ÊÓ

In an experiment on the specilic heat of a metal a \(0.20 \mathrm{~kg}\) block of the metal at \(150^{\circ} \mathrm{C}\) is dropped in a copper calorimeter (of water equivalent \(0.025 \mathrm{~kg}\) ) containing \(150 \mathrm{~cm}^{3}\) of water at \(27^{\circ} \mathrm{C}\). The final temperature is \(40^{\circ} \mathrm{C}\). Calculalc the spocific heat ol the metal.

A body cools in a surrounding of constant temperature \(30^{\circ} \mathrm{C}\). It's heat capacity is \(2 \mathrm{~J} / \mathrm{C}\). Initial temperature of the body is \(40^{\circ} \mathrm{C}\). Assume Newton's law of cooling is valid. The body cools to \(36^{\circ} \mathrm{C}\) in 10 minutes. In further 10 minutes it will cool from \(36 \mathrm{C}\) to (a) \(34.8 \mathrm{C}\) (b) \(32.1 \%\) (c) \(32.8^{\circ} \mathrm{C}\) (d) \(33.6^{\circ} \mathrm{C}\)

Three rods cach of same length and cross section are joined in scrics. The thermal conductivity of the materials are \(k, 2 k\) and \(3 k\) respectively. If one end is kepl al \(200^{\circ} \mathrm{C}\) and the other at \(100^{\circ} \mathrm{C}\). What would be the temperature of the junctions in the steady state? \Lambdassume that no heat is lost duc to radiation from the sides of the rods.

The temperature of the two outer surface of a composite slab consisting of two materials having cocflicient of thermal conductivities \(K\) and \(2 K\), thickness \(x\) and \(4 x\) respectively are \(T_{3}\) and \(T_{1}\left(T_{2}>T_{1}\right) .\) The rate of heat transfer through the slab, in a steady state is \(F\left[\frac{A\left(T_{2}-T_{1}\right) K}{x}\right]\), the value of \(F\) is (a) 1 (b) \(1 / 2\) (c) \(2 / 3\) (d) \(1 / 3\)

For an enclosure maintained at \(2000 \mathrm{~K}\), the maximum radiation occurs at wavelength \(\lambda_{\mathrm{m}^{\prime}}\). If the temperature is raised to \(3000 \mathrm{~K}\), the peak will shift to (a) \(0.5 \lambda_{\mathrm{m}}\) (b) \(\lambda_{m}\) (c) \(\frac{2}{3} \lambda_{m}\) (d) \(\frac{3}{2} \lambda_{m}\)

By which of the following methods could a cup of hot tea lose heat, if placed on metallic table in a classroom? (a) Conduction (b) Convection (c) Radiation (d) Evaporaton of liquid