Intensity of Incident Radiation

The photoelectric effect is the process by which electrons are emitted when electromagnetic radiation takes place, such as a material being hit by light. Photoelectrons are those electrons that get emitted during this effect or process. The photoelectric effect is studied in various subjects ranging from quantum chemistry to condensed matter physics. In 1887 while conducting experiments on Maxwell’s electromagnetic theory, he found a strange phenomenon. A spark gap was used by Hertz to detect electromagnetic waves. A spark gap is created using two sharp electrodes which are placed closely in such a manner that electric sparks are generated.

Photoelectric Effect

It was discovered that ultraviolet rays with a short wavelength falling on the negatively charged plate of a tube that is electrically discharged, make the electric discharge easier. Two zinc plates were installed by Hertz in a vacuum bulb. The plates are connected to a battery using two wires and a galvanometer is installed on one end. Hallwachs observed current flowing through the circuit as soon as ultraviolet rays fall on the negative plate, and the current stops as soon as the ultraviolet rays are stopped from falling on the plate. When there is a shorter wavelength, the light has met one condition. on the positive plate, no current or only feeble current flows which are negligible. However, this was not properly explained by Hallwachs. 

Wavelength was an important factor in the photoelectric effect. Whereas in 1900 Lenard proved that electrons emit when ultraviolet rays fall on the negative plate and the electrons are captivated by the positively charged plate which completes the circuit and current starts to flow through it. The wavelength of the light affects the threshold frequency.  But as soon as the ray falls on the positively charged plate then the electrons which are emitted from the plate are unable to reach the negative plate and complete the circuit because the electrons which are emitted are negative hence the circuit is not complete and the current does not flow. The light which is of short wavelength is more effective than the light which is of longer wavelength from this phenomenon.

Hertz and Lenard’s Observation

Many experiments related to the photoelectric effect were conducted by both scientists using different types of metals and illuminating them with different frequencies of light which are also of different intensities. Photoelectric current strengths and energy of photoelectrons both were measured by them. Different types of results were achieved by them about the photoelectric effect using these experiments. Electromagnetic radiation is also an important factor in the study of the photoelectric effect. 

Let us see a simple experimental arrangement. The figure consists of 2 metallic plates termed P1 and P2 which are placed at some distance in the evacuated tube. P1 is directly in front of W the quartz window, through which light falls on the plate directly. P1 is a cathode plate. A microammeter is connected to both the plates and a divider to commutator C. This experiment can showcase the difference in both the plates and the direction in which potential difference lies can also be changed. The potential difference can be measured using a Voltmeter V.

Effect of Intensity of Incident Radiation

When Ultraviolet rays which have a definite intensity and frequency will fall on plate P1, photoelectrons will get emitted from P1. If plate 2 is at a sufficient position then all the photoelectrons will reach the plate and a photoelectric current of maximum power will flow. If the positive potential is increased it will not alter the current flow in the circuit because the electrons which are emitted already reach P2. Whereas if the intensity of the light ray is doubled then the current will also get doubled. This states that photoelectric current is directly proportionate to the intensity of incident radiation.

Conclusion

The photoelectric effect is a very complex discovery that states various situations in which photoelectrons are produced, it talks about all the possibilities and the results which can be found using the effect. From the light falling on a negative plate to light falling on the positive plate, and from the increment of positive potential which will not affect the experiment to increase the intensity of the light which is directly proportional to the current flowing in the circuit.