Hertz Observation

Photoelectric Emission is a phenomenon in which electrons are ejected from metal surfaces when light is shone upon them, and this phenomenon is known as the photoelectric effect. Photoelectrons are the electrons that are ejected from the body. In this regard, it is important to note that the emission of photoelectrons, as well as the kinetic energy of the photoelectrons ejected from the metal’s surface, is dependent on the frequency of the light that strikes the metal’s surface. Photoemission refers to the process by which photoelectrons are ejected from the surface of the metal as a result of the action of light on the metal.

Discovery

Heinrich Hertz discovered a strange phenomenon in 1887 while conducting experiments to prove Maxwell’s electromagnetic theory of light. Hertz was conducting experiments to prove Maxwell’s electromagnetic theory of light at the time. The presence of electromagnetic waves was detected using a spark gap (two sharp electrodes placed at a small distance from one another so that electric sparks can be generated). He placed it in a dark box to examine it more closely and discovered that the length of the spark had been reduced. Using a glass box caused the length of the spark to increase; however, switching to a quartz box caused the length of the spark to increase even further. This was the first time that the photoelectric effect had been observed.

Wilhelm Hallwachs confirmed these findings a year later, demonstrating that ultraviolet light shining on a zinc plate connected to a battery generated a current (because of electron emission). J.J. Thompson discovered in 1898 that the amount of current produced varied depending on the intensity and frequency of the radiation used.

Lenard discovered in 1902 that the kinetic energy of electrons emitted increased in direct proportion to the frequency of radiation used. Because Maxwell’s electromagnetic theory (which Hertz proved to be correct) predicted that kinetic energy should be dependent only on light intensity(not frequency), this could not be explained .

Einstein would provide an explanation for the photoelectric effect only a few years later, which would bring the issue to a closure.

Setup for Experimentation

The experimental setup used by J.J. Thompson to study this effect (which was later improved by Lenard) is extremely important. It is composed of two zinc plate electrodes that are placed on opposite ends of a glass tube that has been evacuated (a vacuum is maintained). A small quartz window illuminates one of the electrodes that serves as the cathode, which is made up of two electrodes. Because ordinary glass absorbs Ultraviolet light, quartz is used instead. A variable voltage is applied across the two electrodes by means of a battery and a potentiometer, which can be adjusted. Using an ammeter, it is possible to record the current that is flowing through the circuit as the potential and light intensity are changed.

Recordings

The photoelectric Current is directly proportional to the intensity of light that falls on the electrode.It was noted that the current increases in proportion to the intensity of the light source. Also, the current decreases in direct proportion to the decrease in voltage. However, in order to achieve zero current, the voltage must be reversed to a specific V0, which is known as the stopping potential. This means that the voltage must be reversed to such an extent that the electrons are prevented from reaching the anode. This is the maximum amount of kinetic energy that an emitted electron can attain.

The highest possible kinetic energy

KE = eV0

(e denotes the charge carried by the electron.)

Maximum kinetic energy increases proportionally to the frequency of light being observed. When the frequency of light (v) is increased, the stopping potential becomes more negative, implying that the kinetic energy of electrons increases as a result of this.

All frequencies of light, on the other hand, are incapable of causing the development of a photoelectric current. Only light with a frequency above a certain threshold (0) can generate a photoelectric current. This varies depending on the electrode material used. In addition, the maximum kinetic energy of the electrons increases linearly with the frequency of the light being emitted. In fact, if we go below the x-axis, the intercept on the Kinetic energy axis represents the minimum amount of energy required for electron emission; this is referred to as the work function of the material.

Observations

• In the case of any given metal, there is a specific minimum frequency above which the photoelectric effect occurs, which is referred to as the threshold frequency.

• When the frequency of incident light is increased while keeping the number of incident photons constant, maximum kinetic energy of the emitted photoelectrons increases.

• Above the threshold frequency, the maximum kinetic energy of photoelectrons is dependent only on the frequency of incident light, and it is not dependent on the intensity of incident light above the threshold frequency.

• The rate at which photoelectrons are ejected is directly proportional to the intensity of incident light for a given metal and frequency of incident light. The magnitude of the photoelectric current increases as the magnitude of the incident light grows in magnitude.

• The time lag between the incidence of photons and the emission of photoelectric effect radiation is extremely short, measuring less than 10-9 seconds.

Conclusion

When a material absorbs electromagnetic radiation, a phenomenon known as the photoelectric effect occurs, in which electrically charged particles are released from or within the material. When light is shone on a metal plate, the effect is commonly described as the ejection of electrons from the plate. The phenomenon was fundamentally important in the development of modern physics because of the puzzling questions it raised about the nature of light, specifically whether it is a particle or a wave; these doubts were finally resolved by Albert Einstein in 1905 as a result of his research. The effect continues to be important for research in a wide range of fields, from materials science to astrophysics, as well as serving as the basis for a wide range of useful devices in everyday life.