Photoelectric Effect | Definition | Explanation | Application | thetutee |

In the past scientists have always felt difficult to predict the nature of the light and the interaction of the light with the matter. When the light interacts with the matter it releases the charge particles, such as in the case of metals are electron. The radiant energy might be x-rays, gamma rays, radio waves or infrared waves. The materials may be solid, liquid even it can be gas.

In 1905 Albert Einstein proposed a theory which finally solved the mystery about the nature of the light being either particle or the wave. He proposed that depending upon the frequency each wave has a fix amount of energy called quanta, and these packets of energy are not continuous but are discrete. The photons carry energy E = hf where, “h” is the universal constant and “f” is the frequency of the photon. The mathematical equation can be written as E = hc/λ where, “c” is the speed of the light and “λ” is the wavelength of the photon. Form this equation we can predict that the energy of the photon is inversely proportional to its wavelength.

Einstein predicted that a photon would pass through a substance and transmit its energy to an electron. The kinetic energy of the electron would decrease by an amount called the work function (like the electronic work function) as it moved through the metal at high speed and eventually emerged from the material. The work function represents the energy required for the electron to escape the metal. This argument led Einstein to the photoelectric equation Ek = hf, where Ek is the highest kinetic energy of the excited electron, and hf is the kinetic energy of the expelled electron.

The experimental results were not accepted that time by many researchers but with the passage of time new experiments proved that Einstein theory was correct. In 1921 Einstein was awarded Nobel prize in physics for explaining the complete process of the photoelectric effect. According to the quantum principles, the electron occurs in the specific electronic configuration.

The highest level of band energy occupied by the electron is the valence band, the electrical conductivity depends upon the number of electrons in the valence band. In materials like metal (conductors) almost half of is valence band is filled with electrons. These electron in the metal can move form one atom to another atom while carrying current. While in insulators such as glass and rubbers the valence band is filled and their id not enough space for the electrons to move freely.

While in the case of semiconductors the valence band is filled with electron, but a little amount of energy is required for the electron to excite them and move them to the next band which is called as conduction band and here it is comparatively free. The bandgap energy is measured in electron volts.

APPLICATIONS

Using photoelectric effect we can make devices of our own desire, using the band gaps and the light intensity we can produce current with a high response time. Photodiodes and photoelectric cells are some common applications. Phototubes have now been phased out in favor of semiconductor-based photodiodes, which can detect light, quantify its intensity, operate other devices in response to illumination, and convert light to electrical energy.

These electronics operate at low voltages, like their bandgaps, and are utilized in a variety of applications including industrial process control, pollution monitoring, light detection in fiber optic communication systems, photovoltaic cells, scanning, and many more.