EASY
JEE Main/Advance
IMPORTANT
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Which of the following graph shows the correct variation in intensity of heat radiations by black body and frequency at a fixed temperature:

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Important Questions on Heat Transfer

MEDIUM
JEE Main/Advance
IMPORTANT
A red star and a green star radiate energy at the same rate which star is bigger.
EASY
JEE Main/Advance
IMPORTANT
Water is used to cool the radiators of engines in cars because 
EASY
JEE Main/Advance
IMPORTANT
The emissive power of a black body at T=300 K is 100 Watt m-2. Consider a body B of area A=10 m2 coefficient of reflectivity r=0.3 and coefficient of transmission t=0.5. Its temperature is 300 K . Then which of the following is incorrect?
 
HARD
JEE Main/Advance
IMPORTANT

A ring consisting of two parts ADB and ACB of same conductivity k carries an amount of heat H. The ADB part is now replaced with another metal keeping the temperatures T1 and T2 constant. The heat carried increases to 2H. What should be the conductivity of the new ADB part? Given ACBADB=3

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HARD
JEE Main/Advance
IMPORTANT

A sphere of ice at 0°C having initial radius R is placed in an environment having ambient temperature >0°C. The ice melts uniformly, such that shape remains spherical. After a time 't' the radius of the sphere has reduced to r. Which graph best depicts r(t):

MEDIUM
JEE Main/Advance
IMPORTANT

Three bodies A,B and C have equal surface area and thermal emissivities in the ratio eA:eB:eC=1:12:14. All the three bodies are radiating at same rate. Their wavelengths corresponding to maximum intensity are λA,λB and λC respectively and their temperatures are TA,TB and Tc on kelvin scale, then select the incorrect statement

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JEE Main/Advance
IMPORTANT
In a 10 m deep lake, the bottom is at a constant temperature of 4oC. The air temperature is constant at -4oC. The thermal conductivity of ice is 3 times that of water. Neglecting the expansion of water on freezing, the maximum thickness of ice wall:
EASY
JEE Main/Advance
IMPORTANT
If the absorption coefficient and reflection coefficient of a surface of a body are 0.4 and 0.6 respectively then