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# the ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. this statement is known as

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## At a given temperature, the ratio between emissive power and absorptive power is same for all bodies and is equal to the emissive power of black body. This statement is called

Click here👆to get an answer to your question ✍️ At a given temperature, the ratio between emissive power and absorptive power is same for all bodies and is equal to the emissive power of black body. This statement is called Question

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## Weins law

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Updated on : 2022-09-05

Solution Verified by Toppr

Correct option is C)

According to Kirchoff's law : At a given temperature, the ratio between emissive power and absorptive power is same for all bodies and is equal to the emissive power of black body.

This directly implies that good emitters are also good absorbers.

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## [Solved] The ratio of the emissive power and absorptive power of all

Explanation: Kirchhoff’s law: Let E be the total emissive power of the body and α be the absorptivity of the body. Emissivity (ϵ) is the ratio Home Heat Transfer Radiation Laws of Radiation Kirchhoff Law

## The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly blackbody. This statement is known as

This question was previously asked in

BPSC AE Paper 5 (Mechanical) 2012 Official Paper

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Kirchhoff's law Stefan's law Wien law Planck's law

## Answer (Detailed Solution Below)

Option 1 : Kirchhoff's law

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## Detailed Solution

Explanation:Kirchhoff’s law:

Let E be the total emissive power of the body and α be the absorptivity of the body.

Emissivity (ϵ) is the ratio of the emissive power of a non-black body to the black body.

ϵ = EEb

Kirchhoff’s law also holds for monochromatic radiation, for which

Eλ1αλ1=Eλ2αλ2=Ebλαbλ=Ebλ1

∵ Absorptivity of a black body is one.

∴Eλαλ=Ebλ⇒αλ=EλEbλ=ϵλ

Therefore, the monochromatic emissivity of a black body is equal to the monochromatic absorptivity at the same wavelength.

Eλ = αλEbλ

According to Kirchhoff’s law, the ratio of total emissive power to absorptivity is constant for all bodies which are in thermal equilibrium with the surroundings. Therefore, it means that the emissivity of a body is equal to its absorptivity.

Stefan-Boltzmann Law

The thermal energy radiated by a black body per second per unit area is proportional to the fourth power of the absolute temperature and is given by:

E ∝ T4 E = σT4

σ = The Stefan – Boltzmann constant = 5.67 × 10-8 Wm-2K-4

Wien’s displacement law

For a black body emissive spectrum, the wavelength λmax giving the maximum emissive power at a temperature is inversely proportional to the absolute temperature.

λmax = cT λmaxT= c Wavelength =

Speed of LightFrequency

⇒ λ = cV

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Q1. The absorptivity of blackbody equals toQ2. The emissive power of grey body isQ3. If radiant energy EB emitted by the black surface strikes the non-black surface and if the non-black surface has absorptivity α, then it will absorb how much radiation?Q4. A flat plate made of cast iron is exposed to a solar flux of 600 W/m2 at an ambient temperature of 25 °C. Assume that the entire solar flux is absorbed by the plate. Cast iron has a low-temperature absorptivity of 0.21. Use Stefan-Boltzmann constant = 5.669 × 10-8 W/m2-K4. Neglect all other modes of heat transfer except radiation. Under the aforementioned conditions, the radiation equilibrium temperature of the plate is __________ °C (round off to the nearest integer).Q5. Wien’s law is stated as follows: λmT = C, where C is 2898 μm.K and λm is the wavelength at which the emissive power of a black body is maximum for a given temperature T. The spectral hemispherical emissivity (ελ) of a surface is shown in the figure below (1 Å = 10-10 m). The temperature at which the total hemispherical emissivity will be highest is K (round off to the nearest integer).

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## The ratio of the emissive power and absorptive power of all

The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as a) Wien's law b) Stefan's law c) Kirchhoff's law d) Planck's law

Examveda

## The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as

A. Wien's law B. Stefan's law C. Kirchhoff's law D. Planck's law

### Solution(By Examveda Team)

Kirchhoff's law states that the emissivity and the absorptivity of a surface at a given temperature and wavelength are equal.

The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as Kirchhoff's law

## Join The Discussion

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Mohammed 12 day ago

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