A pan filled with hot food cools in 2 minutes from \(94^{\circ}\mathrm{C}\) to \(86^{\circ}\mathrm{C}\) when the room temperature is \(20^{\circ}\mathrm{C}\). How long will it take to cool from \(71^{\circ}\mathrm{C}\) to \(69^{\circ}\mathrm{C}\)?
1. | 50 sec | 2. | 52 sec |
3. | 42 sec | 4. | 48 sec |
Two conducting slabs of heat conductivity \(K_{1} ~ \text{and} ~K_{2}\) are joined as shown in fig. If the temperature at the ends of the slabs are \(\theta_{1}\ and\ \theta_{2} \ (\theta_{1} > \theta_{2} ), \)then the final temperature \( \left(\theta\right)_{m} \)of the junction will be:
1. | \(\frac{K_{1} \theta_{1} + K_{2} \theta_{2}}{K_{1} + K_{2}}\) | 2. | \(\frac{K_{1} \theta_{2} + K_{2} \theta_{1}}{K_{1} + K_{2}}\) |
3. | \(\frac{K_{1} \theta_{2} + K_{2} \theta_{1}}{K_{1} - K_{2}}\) | 4. | None |
A piece of iron is heated in a flame. If it becomes dull red first, then becomes reddish yellow, and finally turns to white hot, the correct explanation for the above observation is possible by using:
1. | Stefan's law | 2. | Wien's displacement law |
3. | Kirchhoff's law | 4. | Newton's law of cooling |
The diagram shows a bimetallic strip used as a thermostat in a circuit. Copper expands more than Invar for the same temperature rise.
What will be switched on when the bimetallic strip becomes hot?
1. | bell only | 2. | lamp and bell only |
3. | motor and bell only | 4. | lamp, bell, and motor |
In an experiment on the specific heat of a metal, a 0.20 kg block of the metal at \(150^{\circ}\mathrm{C}\) is dropped in a copper calorimeter (of water equivalent of 0.025 kg) containing 150 \(c m^{3}\) of water at \(27^{\circ}\mathrm{C}\). The final temperature is \(40^{\circ}\mathrm{C}\). The specific heat of the metal will be: (Heat losses to the surroundings are negligible)
1. \(0 . 40 ~ \text{Jg}^{- 1} \text{K}^{- 1}\)
2. \(0 . 43 ~ \text{Jg}^{- 1} \text{K}^{- 1}\)
3. \(0 . 54 ~ \text{Jg}^{- 1} \text{K}^{- 1}\)
4. \(0 . 61 ~ \text{Jg}^{- 1} \text{K}^{- 1}\)
A brass wire \(1.8\) m long at \(27\) °C is held taut with a little tension between two rigid supports. If the wire is cooled to a temperature of\(-39\) °C, what is the tension created in a wire with a diameter of \(2.0\) mm? (coefficient of linear expansion of brass \(=2.0 \times10^{-5}\) K-1, Young's modulus of brass\(=0.91 \times10^{11}\) Pa)
1. \(3.8 \times 10^3\) N
2. \(3.8 \times 10^2\) N
3. \(2.9 \times 10^{-2}\) N
4. \(2.9 \times 10^{2}\) N
5 g of water at \(30^{\circ} \mathrm{C}\) and 5 g of ice at \(-20^{\circ} \mathrm{C}\) are mixed together in a calorimeter. The water equivalent of the calorimeter is negligible, and the specific heat and latent heat of ice are 0.5 \(\text{cal/g}^{\circ} \mathrm{C}\) and 80 \(\text{cal/g}\), respectively. The final temperature of the mixture is:
1. | \(0^{\circ} \mathrm{C}\) | 2. | \(-8^{\circ} \mathrm{C}\) |
3. | \(-4^{\circ} \mathrm{C}\) | 4. | \(2^{\circ} \mathrm{C}\) |
Three rods made of the same material, having the same cross-sectional area but different lengths 10 cm, 20 cm and 30 cm are joined as shown. The temperature of the junction will be:-
1. \(10.8^{\circ}\mathrm{C}\)
2. \(14.6^{\circ}\mathrm{C}\)
3. \(16.4^{\circ}\mathrm{C}\)
4. \(18.2^{\circ}\mathrm{C}\)
Four rods of the same material with different radii r and length are used to connect two heat reservoirs at different temperatures. In which of the following cases is the heat conduction fastest?
1.
2. r = 3 cm, = 9 cm
3. r = 4 cm, = 8 cm
4. r = 1 cm, = 1 cm