Why is the discovery of the photoelectric effect a milestone in physics?
When X-rays, gamma rays, or certain other wavelengths of light are shined on certain kinds of matter, electrons are ejected. This phenomenon is known as the photoelectric effect.
The photoelectric effect was discovered by German physicist Heinrich Hertz in 1887, and the phenomenon was investigated further in 1902 by the German physicist Philipp Lenard. He showed that, for a given wavelength of light, the electrons had a fixed amount of energy. Weak light produced fewer electrons, but each electron still had just and much energy as if the light had been bright. However, there was a link between wavelength and energy. The shorter the wavelength of light, the more energy the light had. Later, Albert Einstein explained the mechanism of photoelectric effect, and he awarded the Nobel Prize in Physics for the same, in 1921.
When a photon of a certain wavelength, and enough energy, falls on the surface of some metal, it will knock out electrons from the atom. If the photon energy is too low, the electron is unable to escape from the
surface. The energy of the emitted electrons does not depend on the intensity of the incoming light, but only on the energy or frequency of the incoming light.
The photoelectric effect is important in history because it caused scientists to think about light and other forms of electro-magnetic radiation in a different way.
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