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Absorbtion and Emission of Radiation by an Atom APPLET

In this section:

The Optics Book

Light before Quantum Theory
Photoelectric Effect
Quantum Theory
Light: wave or particle?
Faster particles than Light?

## Radiation of a black mass

In this chapter we are going to explain how Planck developed the quantum theory.

Imagine a body with nothing inside and with a small hole at a uniform temperature.  This is called the black body generator of radiation.  Max Planck had the following hypothesis:  The walls of the black body are composed by atoms.  These atoms are small electric oscillators.  Inside the body there is a process of radiation and energy absorption.  During this process, an atom (oscillator) loses energy, thereby emitting electromagnetic waves and therefore absorbing energy from another wave or by thermal agitation.  In a few words, an oscillator absorbs and emits energy.  But that isn’t all.  Planck considered that the energy that is present in the oscillators of the body could only have certain defined values.  These values had to be multiples of hv (h: Planck Constant, v: frequency).

Therefore, when an oscillator loses energy, the energy lost is irradiated in form of packets called “quantum”.  In other words, the small oscillators don’t irradiate continuously, they irradiate in quantums of energy.  The energy of a quantum is proportional to the frequency of the oscillator.  This is symbolized by:

### E µ v

In order to equalize the expression, we introduce a constant, h.

### E=hv

The constant introduced in the equation is called Planck’s constant, which has a value of 6.62x10-34 Js (Joules x second).