Experimental evidence for quantum theory
Experimental evidence for quantum theory
- Photoelectric effect:
To liberate an electron from a metal surface, a quantum or packet of energy called the work function which is characteristic of the metal surface has to be supplied
- Optical spectra:
A line in the optical emission spectrum indicates the presence of a particular frequency f of light and is considered to arise from loss of energy which occurs in an excited atom when an electron jumps directly or in steps from a higher energy level E2 to lower energy level E1.
The frequency of the packet of energy emitted is given by hf = E2 – E1.
- X-ray line spectra:
Electron transition from one shell to another leads to liberation of energy in packets characteristic of the target atom.
Differences between classical theory and quantum theory
| Classical(wave) theory | Quantum theory |
| It allows continuous absorption and accumulation of energy. | No continuous absorption allowed. The energy is either absorbed or rejected. |
| Energy of radiation is evenly distributed over the wave front. | Energy is radiated, propagated and absorbed in packets (quanta or photons). |
| What matters is total energy of the incident radiation (beam). | What matters is the energy of individual photon. |
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