A capacitor can get charged when exposed to light or electromagnetic radiation through a process known as the photoelectric effect. The photoelectric effect occurs when photons (particles of light) interact with a material, causing the ejection of electrons from the surface of the material.
Here's a simplified explanation of how a capacitor can get charged through the photoelectric effect:
The capacitor consists of two conductive plates separated by an insulating material called a dielectric.
When light or electromagnetic radiation falls onto one of the plates, the photons carry energy. If the energy of the photons is sufficient, they can transfer that energy to the electrons in the material on the plate.
If the energy of the photons surpasses the material's work function (the minimum energy required to remove an electron from the material), the electrons near the surface of the plate can be "knocked out" or ejected from their atoms. This is called photoemission.
The ejected electrons become free charges in the material and can move towards the other plate of the capacitor.
The movement of electrons creates an imbalance of charges, resulting in one plate becoming positively charged (due to the loss of electrons) and the other plate becoming negatively charged (due to the accumulation of electrons).
This charge separation creates an electric field between the plates, and a voltage is established across the capacitor.
It's important to note that the photoelectric effect is more commonly observed in materials with low work functions, such as metals. Additionally, the efficiency and extent of the charging depend on factors like the intensity and frequency (energy) of the incident light, the material properties, and the design of the capacitor.
The photoelectric effect is a fundamental phenomenon in physics and has applications in various technologies, including solar cells, photodetectors, and photomultiplier tubes.