The two ends of a rod of length L and a uniform cross-sectional area A are kept at two temperatures T1 and T2T1> T2.The rate f heat transfer, dQdt, through the rod in a steady state is given by 

(1) dQdt=KLT1-T2A                       

(2) dQdt=KLT1-T2LA

(3) dQdt=KLAT1-T2                     

(4) dQdt=KAT1-T2L

Subtopic:  Conduction |
 87%
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 |
 82%
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, it's Young’s modulus is \(Y\) and the coefficient of linear expansion is \(\alpha.\) If the temperature of the rod is increased by \(\Delta t^{\circ} \text{C},\) 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 |
 82%
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 |
 67%
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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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. the 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 |
 75%
From NCERT
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The ratio of thermal conductivity of two rods of different material is 5 : 4. The two rods of same area of cross-section and same thermal resistance will have the lengths in the ratio 

(1) 4 : 5             

(2) 9 : 1

(3) 1 : 9             

(4) 5 : 4

Subtopic:  Conduction |
 72%
From NCERT
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In variable state, the rate of flow of heat is controlled by
(1) Density of material               

(2) Specific heat

(3) Thermal conductivity             

(4) All the above factors

Subtopic:  Conduction |
 70%
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