Physics notes 1

Seite 1

Black body radiation

Black body-Ideal body which absorbs all radiations incident upon it

Radiations can be of any frequency and wavelength

At room temp. most radiations are infrared, even the ones emitted by humans.

In the laboratory, a hollow object with a small hole that leads to its interior can be considered to be a black body.

An incident ray on the opening of the box will trap the ray, causing reflections back and forth within the box until it is absorbed by it.

The walls of the cavity are constantly absorbing and emitting radiation , although the properties of the radiation is what we are interested in.

The black body radiates more when it is hot than is cold.

The spectrum of a hot black body has its peak at a higher frequency than that of a cooler one.

Spectral Distribution of energy in radiation depends only on the temperature of the body.

Higher the temp, there will be greater amount of radiation --- and higher will be the frequency at which maximum emission occurs.

Seite 2

Ultra-Violet Catastrophe

19th century, Lord Rayleigh and James Jeans