When 1 kg of ice at 0°C melts to water at 0°C, the resulting change in its entropy, taking latent heat of ice to be 80 cal/g, is

(1)  8×104 cal/K                                     

(2)  80 cal/K

(3)  293 cal/K                                         

(4)  273 cal/K

Subtopic:  Calorimetry |
NEET - 2011
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A cylindrical metallic rod in thermal contact with two reservoirs of heat at its two ends conducts an amount of heat Q in time t. The metallic rod is melted and the material is formed into a rod of half the radius of the original rod. What is the amount of heat conducted by the new rod when placed in thermal contact with the two reserviors in time t ?

(1)Q/4                                         

(2)Q/16

(3)2Q                                           

(4)Q/2

Subtopic:  Conduction |
 56%
From NCERT
NEET - 2010
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The total radiant energy per unit area per unit time, normal to the direction of incidence, received at a distance R from the centre of a star of radius r,whose outer surface radiates as a black body at a temperature TK is given by 

(a) σr2T4/R2                                       (b) σr2T4/4πr2

(c) σr4T4/r4                                        (d) 4π σr2T4/R2

(where σ is Stefan's constant)

Subtopic:  Stefan-Boltzmann Law |
 60%
From NCERT
NEET - 2010
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A black body at 227°C radiates heat at the rate of 7 cal cm-2s-1. At a temperature of 727°C, the rate of heat radiated in the same units will be 

(1) 60                                     

(2) 50

(3) 112                                   

(4) 80

Subtopic:  Stefan-Boltzmann Law |
 84%
From NCERT
NEET - 2009
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On a new scale of temperature (which is linear) and called the W scale, the freezing and boiling points of water are 39°W and 239°W respectively. What will be the temperature on the new scale, corresponding to a temperature of 39°C on the Celsius scale?

(1) 78°W                                   

(2) 117°W

(3) 200°W                                 

(4) 139°W

Subtopic:  Temperature and Heat |
 81%
From NCERT
NEET - 2008
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To keep constant time, watches are fitted with balance wheel made of -

(1) Invar                                 

(2) Stainless steel

(3) Tungsten                             

(4) Platinum

Subtopic:  Thermal Expansion |
 58%
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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The pressure applied from all directions on a cube is P. How much its temperature should be raised to maintain the original volume ? The volume elasticity of the cube is  β and the coefficient of volume expansion is α -

(1) Pαβ                                 

(2) Pαβ

(3) Pβα                                 

(4) αβP

 

Subtopic:  Thermal Expansion |
 66%
From NCERT
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Under steady state, the temperature of a body 

(1) Increases with time

(2) Decreases with time

(3) Does not change with time and is same at all the points of the body

(4) Does not change with time but is different at different points of the body

Subtopic:  Conduction |
 54%
From NCERT
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The coefficient of thermal conductivity depends upon

(1) Temperature difference of two surfaces

(2) Area of the plate

(3) Thickness of the plate

(4) Material of the plate

Subtopic:  Conduction |
 76%
From NCERT
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