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. α12l= α22l1

3. α1l= α2l2

4. α1l= α2l1

Subtopic:  Thermal Expansion |
 83%
From NCERT
NEET - 2016
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A black body is at a temperature of 5760 K. The energy of radiation emitted by the body at a wavelength of 250 nm is U1, at a wavelength of 500 nm is U2 and that at 1000 nm is U3. Given Wien's constant b=2.88×106 nm-K, which of the following is correct?
1. U3=0       
2. U1>U2
3. U2>U1     
4. U1=0

Subtopic:  Wien's Displacement Law |
 52%
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%
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 |
 74%
From NCERT
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Two identical plates of different metals are joined to form a single plate whose thickness is double the thickness of each plate. If the coefficients of conductivity of each plate are 2 and 3 respectively, then the conductivity of the composite plate will be:
1. 5
2. 2.4
3. 1.5                 
4. 1.2

Subtopic:  Conduction |
 74%
From NCERT
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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%
From NCERT
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