# With neat labelled circuit diagram, describe an experiment to study the characteristics of photoelectric effect.

Question: With neat labelled circuit diagram, describe an experiment to study the characteristics of photoelectric effect.

The photoelectric effect is the phenomenon of emission of electrons from a metal surface when it is exposed to light of a suitable frequency. To study this effect, we can use the following experimental setup:

![Photoelectric effect experiment](^1^)

The setup consists of an evacuated glass tube with a quartz window, which allows only ultraviolet light to enter. Inside the tube, there are two metal plates: an emitter E and a collector C. The emitter is a photosensitive metal, such as zinc or potassium, which can emit electrons when illuminated by light. The collector is connected to the positive terminal of a battery, while the emitter is connected to the negative terminal through a variable resistor R and an ammeter A. A voltmeter V is connected across the plates to measure the potential difference between them.

When ultraviolet light of frequency ν falls on the emitter, electrons are ejected from its surface. These electrons are attracted by the collector and form a current in the circuit, which is measured by the ammeter. The potential difference between the plates can be varied by changing the resistance R. When the potential difference is positive, it accelerates the electrons and increases the current. When the potential difference is negative, it opposes the electrons and decreases the current. At a certain negative potential, called the stopping potential, the current becomes zero. This means that the electrons have just enough kinetic energy to reach the collector.

By performing this experiment, we can study the following characteristics of the photoelectric effect:

- The number of electrons emitted per second, or the photoelectric current, is proportional to the intensity of light, provided the frequency is above a certain threshold value. This means that more light causes more electrons to be emitted.

- The kinetic energy of the emitted electrons, or the stopping potential, depends only on the frequency of light, and not on its intensity. This means that higher frequency light causes faster electrons to be emitted.

- There is a minimum frequency of light, called the threshold frequency, below which no electrons are emitted, regardless of the intensity of light. This means that there is a minimum energy required to eject electrons from the metal.

These characteristics can be explained by Einstein's photoelectric equation, which states that the energy of a photon of light is equal to the sum of the work function of the metal and the kinetic energy of the emitted electron:

$$hv = \phi + \frac{1}{2}mv^2$$

where h is Planck's constant, v is the frequency of light, ϕ is the work function of the metal, m is the mass of the electron, and v is the speed of the electron.