# <!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> A certain quantity of water cools from $$70^{\circ}\mathrm{C}$$ to $$60^{\circ}\mathrm{C}$$ in the first 5 minutes and to $$54^{\circ}\mathrm{C}$$ in the next 5 minutes.  The temperature of the surroundings will be:  1. $$45^{\circ}\mathrm{C}$$ 2. $$20^{\circ}\mathrm{C}$$ 3. $$42^{\circ}\mathrm{C}$$ 4. $$10^{\circ}\mathrm{C}$$

Subtopic:  Newton's Law of Cooling |
76%
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NEET - 2014
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The temperature of a wire of length 1 meter and an area of cross-section 1cm2 is increased from $$0^{\circ} \mathrm {C}$$ to $$100^{\circ} \mathrm {C}$$. If the rod is not allowed to increase in length, the force required will be: $$(\alpha = 10^{-5}/ ^{\circ} \mathrm {C} ~\text{and} ~Y = 10^{11} ~\text{N/m}^2)$$

 1 $$10^3 \mathrm{~N}$$ 2 $$10^4 \mathrm{~N}$$ 3 $$10^5 \mathrm{~N}$$ 4 $$10^9 \mathrm{~N}$$
Subtopic:  Thermal Stress |
81%
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A metal bar of length $$L$$ and area of cross-section $$A$$ is clamped between two rigid supports. For the material of the rod, its Young’s modulus is $$Y$$ and the coefficient of linear expansion is $$\alpha$$. If the temperature of the rod is increased by $$\Delta t^{\circ} \mathrm{C}$$, the force exerted by the rod on the supports will be:
1. $$YAL\Delta t$$
2. $$YA\alpha\Delta t$$
3. $$\frac{YL\alpha\Delta t}{A}$$
4. $$Y\alpha AL\Delta t$$

Subtopic:  Thermal Stress |
81%
From NCERT
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When two ends of a rod wrapped with cotton are maintained at different temperatures and, after some time, every point of the rod attains a constant temperature, then:

 1 Conduction of heat at different points of the rod stops because the temperature is not increasing 2 The rod is a bad conductor of heat 3 Heat is being radiated from each point of the rod 4 Each point of the rod is giving heat to its neighbour at the same rate at which it is receiving heat
Subtopic:  Conduction |
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Mud houses are cooler in the summer and warmer in the winter because:

 1 the mud is a superconductor of heat. 2 the mud is a good conductor of heat. 3 the mud is a bad conductor of heat. 4 None of the above

Subtopic:  Conduction |
81%
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One likes to sit in the sunshine in the winter season, because:

 1 The air around the body is hot, and the body absorbs heat from it. 2 we get energy from the sun. 3 we get heat by conduction from the sun. 4 None of the above

Subtopic:  Conduction |
64%
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Air is a bad conductor of heat or partly conducts heat. Still, a vacuum is to be placed between the walls of the thermos flask because:

 1 it is difficult to fill the air between the walls of the thermos flask. 2 due to more pressure of air, the thermos can get cracks. 3 by convection, heat can flow through the air. 4 on filling the air, there is no advantage.
Subtopic:  Convection |
79%
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While measuring the thermal conductivity of a liquid, we keep the upper part hot and the lower part cool, so that:

 1 convection may be stopped. 2 radiation may be stopped. 3 heat conduction is easier downwards. 4 it is easier and more convenient to do so.

Subtopic:  Convection |
62%
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On a clear sunny day, an object at temperature T is placed on the top of a high mountain. An identical object at the same temperature is placed at the foot of the mountain. If both the objects are exposed to sun-rays for two hours in an identical manner, the object placed on the top of a mountain will register a temperature:

 1 higher than the object at the foot. 2 lower than the object at the foot. 3 equal to the object at the foot. 4 none of the above.

52%
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Taking into account the radiation that a human body emits which of the following statements is true?

 1 The radiation is emitted only during the day. 2 The radiation is emitted during the summers and absorbed during the winters. 3 The radiation emitted lies in the ultraviolet region and hence is not visible. 4 The radiation emitted is in the infra-red region.