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Kirchoff's Law

Which one of ...

Question

Which one of the following statements is not true about thermal radiations?

A

All bodies emit thermal radiations at all temperatures

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B

Thermal radiations are electromagnetic waves

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C

Thermal radiations are not reflected from a mirror

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D

Thermal radiations travel in free space with a velocity of

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Solution

The correct option is C
Thermal radiations are not reflected from a mirror

Thermal radiations obey the laws of reflection.

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Similar questions

Q. Assertion : Like light radiation, thermal radiations are also electromagnetic radiation.
Reason : Thermal radiation require no medium for propagation.

Which one of the following statements is not true about thermal radiations?

Q. Assertion (A): Thermal radiations are electromagnetic radiation with wave lengths greater than visible light.
Reason (R): Thermal radiations can propagate through vacuum.

Q. Thermal radiations are electromagnetic waves belonging to

Q. All bodies emit heat energy from their surfaces by virtue of their temperature. This heat energy is called radiant energy of thermal radiation. The heat that we receive from the sun is transferred to us by a process which, unlike conduction or convection, does not require the help of a medium in the intervening space which is almost free of particles. Radiant energy travels in space as electromagnetic spectrum. Thermal radiations travel through vacuum with the speed of light. Thermal radiations obey the same laws of reflection and refraction as light does. They exhibit the phenomena of interference, diffraction and polarisation as light does.
The emission of radiation from a hot body is expressed in terms of that emitted from a reference body (called the black body) at the same temperature. A black body absorbs and hence emits radiations of all wavelengths. The total energy

E

emitted by a unit area of a black body per second is given by

E = σ T^{4}

T

is the absolute temperature of the body and

σ

is a constant known as Stefan's constant. If the body is not a perfect black body, then

E = ε σ T^{4}

ε

is the emissivity of the body.
In which region of the electromagnetic spectrum do thermal radiations lie?

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