Assertion (A): |
Houses made of concrete roofs overlaid with foam keep the room hotter during |
Reason (R): |
The layer of foam insulation prohibits heat transfer, as it contains air pockets. |
1. | (A) is True but (R) is False. |
2. | (A) is False but (R) is True. |
3. | Both (A) and (R) are True but (R) is not the correct explanation of (A). |
4. | Both (A) and (R) are True and (R) is the correct explanation of (R). |
A cup of coffee cools from \(90^{\circ}\text{C}\) \(80^{\circ}\text{C}\) in \(t\) minutes, when the room temperature is \(20^{\circ}\text{C}\). The time taken by a similar cup of coffee to cool from \(80^{\circ}\text{C}\) \(60^{\circ}\text{C}\) at room temperature same at \(20^{\circ}\text{C}\) is:
1. \(\dfrac{10}{13}t\)
2. \(\dfrac{5}{13}t\)
3. \(\dfrac{13}{10}t\)
4. \(\dfrac{13}{5}t\)
Consider a compound slab consisting of two different materials having equal thicknesses and thermal conductivities K and 2K, respectively. The equivalent thermal conductivity of the slab will be:
1. | 2. | ||
3. | 4. |
We consider the radiation emitted by the human body. Which of the following statements is true:
1. | The radiation emitted is in the infrared region |
2. | The radiation is emitted only during the day |
3. | The radiation is emitted during the summers and absorbed during the winters |
4. | The radiation emitted lies in the ultraviolet region and hence is not visible |
A cylindrical rod has temperatures at its ends. The rate of flow of heat is cal/sec. If all the linear dimensions are doubled while keeping the temperature constant, then the rate of flow of heat will be:
1.
2.
3.
4.
A black body has a wavelength corresponding to maximum energy at 2000 K. Its wavelength corresponding to maximum energy at 3000 K will be:
1.
2.
3.
4.
Unit of Stefan's constant is:
1. Watt-m2-K4
2. Watt-m2/K4
3. Watt/m2–K
4. Watt/m2 K4
Consider two rods of the same length and different specific heats \((S_1,S_2)\) conductivities \((K_1,K_2)\) and area of cross-sections \((A_1,A_2)\) and both having temperature \(T_1\) and \(T_2\) at their ends. If the rate of loss of heat due to conduction is equal, then:
1. \(K_1A_1=K_2A_2\)
2. \(\frac{K_1A_1}{S_1}=\frac{K_2A_2}{S_2}\)
3. \(K_2A_1=K_1A_2\)
4. \(\frac{K_2A_1}{S_2}=\frac{K_1A_2}{S_1}\)