Photo effect

Physics > Photoelectric effect

Consider the phenomenon and laws photoelectric effect Einstein: the energy supply of photons, the quantum nature of light and electrons, the phenomenon of the photoelectric effect.

Electrons come from a substance that absorbs energy in electromagnetic rays, which causes a photoelectric effect.

Learning challenge

• Find out how Albert Einstein managed to solve the paradox of the photoelectric effect.

Key points

• The energy emitted by electrons is based solely on the frequency of the incoming light, not on its intensity.
• Einstein understood the photoelectric effect by characterizing light in terms of discrete particles.
• Further research helped to understand the quantum nature of light and electrons, which led to the duality of wave particles.

Terms

• Blackbody radiation is a type of EM radiation inside or around the body, which is in thermodynamic balance with the environment.
• Photoelectron – electrons emitted by a substance that absorb energy from EM rays.
• Duality of wave particles – all particles have the characteristics of waves and particles.

When light hits the surface of a substance, it releases electrons. This is called

by the photoelectric effect, and electrons by photoelectrons.

Electrons come from matter absorbed by light

To create the photoelectric effect, photons with an energy reserve of several electron volts to 1 MeV are needed. His research led to a better understanding of the quantum nature of light and electrons, and also influenced the creation of the concept of the duality of wave particles. This effect is also widely used to study the energy levels of electrons in matter.

In 1887, Heinrich Hertz became the first to identify the photoelectric effect. At that time, electrons were not yet known, but Hertz noticed that when a metal was illuminated with ultraviolet light, an electric current was formed. In the early 20th century, physicists confirmed that:

• the energy of individual photoelectrons increases with frequency, but is not related to intensity.
• the photoelectric current was determined by the light intensity.

These findings have become a real discovery for many physicists. Then light was perceived as a wave phenomenon. The energy carried by the wave must be based solely on amplitude, so the frequency dependence of the energy simply does not make sense.

In 1905, Albert Einstein found the solution. He simply described light as something represented by discrete quanta (photons) rather than continuous waves. He took the theory of black body radiation by Max Planck as a basis and assumed that in each quantum the energy will be equated to the frequency multiplied by Planck’s constant. As the frequency increases, each photon carries more energy, which means that the energy of each outgoing photoelectron increases.

Maximum ejected electron energy: K_max = hf – φ (h is Planck’s constant, f is the frequency of the incoming photon). The term φ is a work function. This is the minimum energy needed to remove an electron from the metal surface. Work function: φ = hf₀ (f₀ Is the threshold frequency of the metal for the onset of the photoelectric effect).

Is light made of particles or waves? Young’s experience with slits showed that we are facing a wave, but the photoelectric effect indicates particles. Broglie solved the problem: light has the properties of particles and waves.

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