# The coefficients of linear expansion of brass and steel rods are α1 and α2, lengths of brass and steel rods are l1 and l2 respectively. If (l2 - l1) is maintained the same at all temperatures, Which one of the following relations holds good? 1. α1l22 = α2l12 2. α12l2 = α22l1 3. α1l1 = α2l2 4. α1l2 = α2l1

Subtopic:  Thermal Expansion |
83%
From NCERT
NEET - 2016
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A piece of ice falls from a height $$h$$ so that it melts completely. Only one-quarter of the heat produced is absorbed by the ice, and all energy of ice gets converted into heat during its fall. The value of $$h$$ is: (Latent heat of ice is $$3.4\times10^5$$ J/kg and $$g=10$$ N/kg)

 1 $$544$$ km 2 $$136$$ km 3 $$68$$  km 4 $$34$$ km
Subtopic:  Calorimetry |
75%
From NCERT
NEET - 2016
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The two ends of a metal rod are maintained at temperatures $$100^{\circ}\mathrm{C}$$ and $$110^{\circ}\mathrm{C}$$. The rate of heat flow in the rod is found to be 4.0 J/s. If the ends are maintained at temperatures $$200^{\circ}\mathrm{C}$$ and $$210^{\circ}\mathrm{C}$$, the rate of heat flow will be:
1. 44.0 J/s
2. 16.8 J/s
3. 8.0 J/s
4. 4.0 J/s

Subtopic:  Conduction |
87%
From NCERT
NEET - 2015
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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%
From NCERT
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%
From NCERT
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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%
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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 |
74%
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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 |
80%
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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 |
63%
From NCERT
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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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