What is photoelectric effect? Explain the effect of increase (i) frequency (ii) intensity of incident radiation on photoelectric current with suitable graphs.

The photoelectric effect is a phenomenon in physics where electrons are emitted from a material when it is exposed to light or electromagnetic radiation of a certain frequency. This effect played a crucial role in the development of quantum mechanics and the understanding of the particle-like nature of light.

Here's a brief explanation of the photoelectric effect and its dependence on the frequency and intensity of incident radiation:

Photoelectric Effect: When light or electromagnetic radiation of sufficient energy (i.e., photons with a minimum energy called the "threshold energy" or "work function") strikes the surface of a material, it can eject electrons from the material. This emission of electrons is known as the photoelectric effect. The ejected electrons are referred to as photoelectrons.
Now, let's consider the effect of increasing the frequency and intensity of incident radiation on the photoelectric current:

(i) Effect of Increasing Frequency:

When the frequency of incident radiation is increased, the energy of individual photons also increases (since E = hν, where E is the energy, h is Planck's constant, and ν is the frequency).
If the frequency becomes greater than or equal to the threshold frequency (ν₀) of the material (the minimum frequency required to release electrons), more electrons are emitted.
The photoelectric current (the flow of photoelectrons) increases with increasing frequency, but it does so linearly only up to a certain point, after which it plateaus. This is because once the energy of the photons exceeds the work function of the material, further increases in frequency do not affect the kinetic energy of the emitted electrons. The graph depicting this relationship is shown below, with current (I) on the y-axis and frequency (ν) on the x-axis:
Photoelectric Effect - Increasing Frequency

(ii) Effect of Increasing Intensity:

Increasing the intensity of incident radiation means that more photons per unit time are striking the material's surface.
This results in more photoelectrons being emitted per unit time, leading to an increase in photoelectric current.
Importantly, the kinetic energy of the emitted electrons does not change with an increase in intensity.
The graph for the effect of increasing intensity would show a linear relationship between current (I) and intensity (I₀), as shown below:
Photoelectric Effect - Increasing Intensity

In summary, increasing the frequency of incident radiation increases the photoelectric current as long as the frequency is above the threshold frequency, while increasing the intensity increases the current without affecting the kinetic energy of the emitted electrons. These observations are consistent with the quantum nature of light and the photoelectric effect's fundamental principles.