Photoelectric Effect

Basic Definition

PHOTOELECTRIC EFFECT| Photoelectric effect is the emission of electrons or other free carriers when electromagnetic radiation, like light, hits a material. Electrons emitted in this manner can be called photoelectrons. This phenomenon is commonly studied in electronicphysics and in fields of chemistry such as quantum chemistry and electrochemistry.

A Brief History -

This effect was observed earlier before Albert Einstein gave the theory for it.

In 1839, Alexandre Edmond Becquerel discovered the photovoltaic effect while studying the effect of light on electrolytic cells. Though not equivalent to photoelectric effect.

The first of these phenomena was discovered by Heinrich Hertz and Wilhelm Hallwachsin 1887.

In 1887, Heinrich Hertz observed the photoelectric effect and the production and reception of electromagnetic waves.

The second was first announced by Philipp Lenard in 1900.

Albert Einstein's 1905 research paper

ALBERT EINSTEIN| In 1905, Albert Einstein solved this apparent paradox by describing light as composed of discrete quanta, now called photons, rather than continuous waves. Based upon Max Planck's theory of black-body radiation, Einstein theorized that the energy in each quantum of light was equal to the frequency multiplied by a constant, later called Planck's constant. A photon above a threshold frequency has the required energy to eject a single electron, creating the observed effect.

This discovery led to the quantum revolution in physics and earned Einstein the Nobel Prize in Physics in 1921.

Particle Nature of Light

The photoelectric effect supports the particle modelbecause the effect depends on the frequency and not the intensity of the light. This means that particles of certain energy were creating the effect, not the absorption of a wave.

Applications of photoelectric effect

Image sensors

Video camera tubes in the early days of televisionused the photoelectric effect, for example, Philo Farnsworth's "Image dissector" used a screen charged by the photoelectric effect to transform an optical image into a scanned electronic signal.

Some other applications are -

Photomultipliers, Night vision devices, Spacecrafts, Gold-Leaf Electroscope , Photoelectron spectroscopy, moon dust etc.

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