Two rods, A and B, of different materials having the same cross-sectional area are welded together as shown in the figure. Their thermal conductivities are K1 and K2. The thermal conductivity of the composite rod will be:

   

1. K1+K22
2. 3K1+K22
3. K1+K2
4. 2K1+K2

Subtopic:  Conduction |
 78%
From NCERT
NEET - 2017
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A spherical black body with a radius of 12 cm radiates 450-watt power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watts would be:

1. 225 2. 450
3. 1000 4. 1800
Subtopic:  Stefan-Boltzmann Law |
 74%
From NCERT
NEET - 2017
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Two identical bodies are made of a material for which the heat capacity increases with temperature. One of these is at 100° C, while the other one is at 0° C. If the two bodies are brought into contact, then assuming no heat loss, the final common temperature is -

(1) 50° C

(2) more than 50°C

(3) less than 50°C but greater than 0°C

(4)  0 C0

Subtopic:  Calorimetry |
 55%
From NCERT
NEET - 2016
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A body cools from a temperature 3T to 2T in10 minutes. The room temperature is T. Assume that Newton's law of cooling is applicable. The temperature of the body at the end of next 10 minutes will be -

(a) 74T    (b) 32T

(c) 43T    (d) T

 

Subtopic:  Newton's Law of Cooling |
 71%
From NCERT
NEET - 2016
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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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Two metal wires of identical dimensions are connected in series. If σ1 and σ2 are the conductivities of the metal wires respectively, the effective conductivity of the combination is

1. 2σ1σ2σ1+σ2

2. σ1σ22σ1σ2 

3. σ1+σ2σ1σ2  

4. σ1σ2σ1+σ2

Subtopic:  Conduction |
 74%
From NCERT
NEET - 2015
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The value of coefficient of volume expansion of glycerin is 5x10-4 K-1. The fractional change in the density of glycerin for a rise of 40°C in its temperature is -

(1) 0.015

(2) 0.020

(3) 0.025

(4) 0.010

Subtopic:  Thermal Expansion |
 79%
From NCERT
NEET - 2015
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Steam at 100°C is passed into 20 g of water at 10°C. When water acquires a temperature of 80°C, the mass of water present will be (Take specific heat of water=1 cal g-1 °C-1 and latent heat of steam = 540 cal g-1)

(a) 24 g                       

(b) 31.5g

(c) 42.5 g                   

(d) 22.5 g

Subtopic:  Calorimetry |
 67%
From NCERT
NEET - 2014
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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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