Radiation

What is radiation? Give two examples.

The ratio of radiation heat flow and temperature different (hr)

E.g. operation of furnace, thermal cracking, combustion of fossil fuel

What is speed of light?

C = 2.998 x 108 m/s.

What is a radiation characterized by?

Its wave length λ or its frequency v--- c = v λ

Why is called blackbody?

- Because it doses not reflect any radiation.

- Is a perfect emitter.

- Absorbs the incident radiation irrespective of its wave length

- Emission from a blackbody occurs in all possible directions

- A blackbody is an ideal substance, whose emissivity and absorptive are both equal to unity.

What is gray body?

A Substance whose emissivity and absorpitivity are independent of wave length.

Write three laws of radiation?

The Stefan-Boltzmann law:

Calculate the total amount of radiation of all wavelength emitted in all possible directions by blackbody.

Eb = σ T4

Eb = total emissive power of blackbody

σ = Stefan-Boitzmann constant = 5.729 x 10-8

T = temperature (K) surface temperature

Kirchhoff's law:

The emissivity of a body, which is in thermal equilibrium with it's surrounding is equal ti its absorpitivity. ε = α

Weins's displacement law:

It state thast is the wave length λmax is inversely proportional to the temperature of the blackbody. λmax α 1/T -- λmax T = constant = 2898μmk

Example:

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Example:

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