Experimental Study of the Photoelectric Effect

When light shines on a substance, it emits electrons or other free carriers, which is known as the photoelectric effect. Photo electrons are electrons that are emitted in this manner. 

When a metal is exposed to light, the photoelectric effect occurs, in which the metal emits electrons from its valence shell. Photoelectron is the name given to the released electron, while photoemission is the term used to describe the process.

Scientists have been trying to understand how light behaves by categorising it as a wave or a particle based on its qualities. Light appears to behave in two ways: as a particle and as a wave. The wave nature of light is supported by properties such as interference, dispersion, and diffraction, but the quantisation and particle character of light is supported by phenomena such as the photoelectric effect. We can say that light has both a wave and a particle character.

While this whole concept is intriguing, it isn’t remarkable. All forms of electromagnetic radiation transfer energy, and it’s easy to imagine this energy being used to drive tiny negative charge particles loose from the surface of a metal where they weren’t all that tightly contained, to begin with. 

However, the modern physics age is characterised by entirely unexpected and incomprehensible discoveries. The photoelectric effect was studied further, and the results contradicted the classical idea of electromagnetic radiation. Light didn’t behave the way it was meant to when it came in contact with electrons. 

Effect of Intensity of Light on Photoelectric Current

The frequency of incident light and the accelerating potential V of the anode are kept constant to evaluate the influence of incident light intensity on photoelectric current. The potential of A is kept positive about that of C, causing the electrons released by C to be drawn to A. The photoelectric current is then measured as the intensity of the incident light is altered. On the x-axis, light intensity is plotted against photocurrent on the y-axis. The number of electrons emitted each second, or photocurrent, is proportional to the intensity of the input light.

Effect of Potential Difference on the Photoelectric Current

For a given metallic surface C, keeping the intensity (I1) and frequency of the incident radiation constant, the effect of electrical phenomenon between the plates on the photoelectric current is often studied. 

When the positive potential of A is increased, the photoelectric current is additionally increased. However, if the positive potential is further increased such that it is large enough to gather all the photoelectrons emitted from plate C, the photoelectric current reaches a specific maximum value and this current is understood as saturation current. If the potential of plate A is formed negative, the photocurrent doesn’t immediately drop to zero but flows within the same direction as for positive potential. If the negative or retarding potential is further increased, the photocurrent decreases and eventually becomes zero at a selected value. Thus, the minimum negative (retarding) potential given to the anode that the photocurrent becomes zero is termed the cut-off or stopping potential. 

The kinetic energy associated with a photoelectron released at a velocity of  Vmax is

mv2max if m is the mass of the photoelectron.

Because the fastest electron is merely prevented from reaching plate A at the stopping potential Vo, the effort was done in bringing the fastest electron to rest equals the kinetic energy of the fastest electron. Because the fastest electron is merely prevented from reaching plate A at the stopping potential Vo, the effort was made in bringing the fastest electron to rest equals the kinetic energy of the fastest electron.

mv2max = eVo

According to the aforementioned equation, the stopping potential is determined by the velocity of the fastest electron.

Effect of Frequency of Incident Radiation on Stopping Potential

The influence of the frequency of incident radiations on stopping potential is investigated while keeping the photosensitive plate (C) and intensity of incident radiation constant. The photoelectric current varies with the applied potential difference V for three distinct frequencies, as shown in the figure. According to the graph, the higher the frequency of incident radiation, the higher the stopping potential Vo. The equivalent stopping potentials for frequencies  v3 > v2 > v1 are in the order (Vo)3 > (Vo)2 > (Vo)1.

A straight line is obtained when the frequency of incident radiation is plotted against the matching stopping potential. The value of the stopping potential is 0 at frequency vo, according to this graph. This frequency is referred to as the photo metal’s threshold frequency. Above this frequency, the photoelectric effect occurs, and below it, it stops. As a result, threshold frequency is defined as the lowest frequency of incident radiation below which photoelectric emission is impossible, regardless of incident radiation intensity. Various metals have different threshold frequencies.

Principle of Photoelectric Effect 

A metal surface is irradiated with light in the photoelectric effect, and when light falls on the metal’s surface, photoemission occurs, and photoelectrons are ejected from the metal’s surface.

The energy of the wave’s photon is transmitted to the metal atom’s electrons, which causes the electrons to get excited and expelled with a certain velocity.

Important Terms Related to Photoelectric Effect 

The work function is the minimum energy required to extract an electron from a metal’s valence shell. It all depends on the metal we’re working with. The photoelectric effect occurs only at frequencies greater than the threshold frequency; if the frequency of the light wave is less than the threshold frequency, the photoelectric effect does not occur.

Threshold frequency: This is the photon’s lowest frequency, just high enough to produce photoelectrons or supply energy equal to the metal’s work function. It all depends on the metal we’re working with.

Conclusion 

We have learned about a phenomenon that can only be described by the particle nature of light in this article. We discovered that a photon is the component particle that makes up light. Photons are energy packets with a certain amount of motion, but their rest mass is zero. We discovered that as the intensity of light increases, the photoelectron’s maximum kinetic energy remains constant, while the photocurrent value increases. For a given metal, the photoelectron’s maximum kinetic energy is solely determined by the incident light’s frequency. The work function is the amount of work that must be done for metal to emit a photoelectron. It is determined by the metal.