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Photoelectricity is a fancy way of saying that light can create electricity by interacting with matter. When light hits certain materials, it can cause electrons to jump out of the material, which produces electricity. This is called the photoelectric effect. The word 'photo' comes from the Greek word for light. The electrons that are released because of the photoelectric effect are called photoelectrons.

Nowadays, the photoelectric effect is used in lots of technology. For example, light meters on cameras use it to automatically adjust the camera's settings based on the amount of light available. Solar cells also use the photoelectric effect to produce electricity from the sun's light. Other devices, like photomultipliers night vision goggles, also use the photoelectric effect to work.

The development of the concept of the photoelectric effect

The photoelectric effect was discovered by a scientist named Heinrich Hertz way back in 1887. He was using a special device to measure something called a spark gap, which is kind of like an electrical spark. To make it easier to see the spark, he did his experiments in a dark box. But then he noticed that the spark got smaller when he was inside the box. So he had to change his experiment and try a different approach.

Figure 2. Hertz’s experiment setup
Figure 2. Hertz’s experiment setup

Even though Heinrich Hertz first saw the photoelectric effect, he didn't actually explain it. That credit goes to Albert Einstein. Another scientist named Robert Millikan didn't believe Einstein's explanation at first. He thought that no electrons would be released in the experiment if it was done correctly. So he did his own experiment in a special vacuum to make sure that nothing else in the atmosphere was affecting his results.

But as it turned out, Millikan's experiment actually confirmed that the photoelectric effect was true. This helped Einstein win the Nobel Prize in 1921 for his theory about the photoelectric effect. And later, in 1923, Millikan himself won a Nobel Prize for his work on the charge of an electron and proving Einstein's theory.

An example of the photoelectric effect

To better understand the photoelectric effect, let's take a closer look at an example. Suppose we have an iron plate from which a photoelectron is emitted with a kinetic energy of.0eV. In order to determine the energy and frequency of the photon that caused this emission, we need to know the work function. The work function is the minimum amount of energy required for a photon to release a photoelectron from the metal plate. For an iron plate, the work function is 4.5eV.

Since the photoelectron has a kinetic energy of 5.0eV, the energy of the photon must be the sum of both energies, as energy is conserved. One electron volt (eV) is equal to 1.6 ⋅ 10^-19 joules. Therefore, the energy of the photon can be calculated by adding the kinetic energy of the photoelectron to the work function. This gives us an energy of 9.5eV, which is equivalent to 1.52 × 10^-18 joules.

To find the frequency of the photon, we need to use the formula E = hf, where h is Planck's constant (6.63 × 10^-34 m^2⋅kg/s). Dividing the energy by Planck's constant gives us the frequency of the light, which is 2.29 × 10^15 Hz. This means that the photon that caused the emission of the photoelectron had a frequency of 2.29 × 10^15 Hz.

How did photoelectricity affect the wave theory of light?

The concept of photoelectricity and the photoelectric effect played a major role in disproving the wave theory of light. According to this theory, light should spread equally over a metal surface, providing energy to each free electron with every incoming wave. With enough energy, each electron should eventually be released from the metal surface. However, we now know that no electrons are emitted if the light wave is below the threshold frequency, which cannot be explained by the wave theory.

In photoelectricity, electricity is generated by the action of light on a material, causing electrons to be ejected from the material. This means that light is producing electricity, and the basic fundamental unit of light is called a photon. The work function is the minimum energy required for a photon to release a photoelectron from a metal plate. The equation used to calculate the energy of a photon is E = hf, where h is Planck's constant (6.63 × 10^-34 m^2⋅kg/s) and f is the frequency of the light.

In summary, photoelectricity and the photoelectric effect have led to significant advancements in our understanding of light and electricity, helping to disprove the wave theory of light and leading to the development of new technologies that rely on the principles of photoelectricity.


What is Einstein’s equation for the photoelectric effect?

E = hf, where E is the photon’s energy, h is the Planck constant, and f is the frequency of the light.

What is the photoelectric effect?

The photoelectric effect is the name given to the emission of electrons by incident electromagnetic radiation (light).

Who discovered the photoelectric effect?

The photoelectric effect was first observed by Heinrich Hertz, who, however, could not explain why it happened. It was Albert Einstein who explained the photoelectric effect, which was later proven by Robert Millikan, even though he was trying to disprove the theory.

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