Describe the construction of photoelectric cell.
A photoelectric cell is device which converts light energy into electrical energy. It works on the principle of photoelectric effect.
Construction : A photoelectric cell consist a small evacuated bulb. A thin layer of an alkali metal is deposited on inner surface of the bulb. The bulb is made of quartz, if cell is used with ultraviolet light. If the cell is to be used with visible light only. the bulb is made of ordinary glass. A small portion of the surface of bulb is left uncoated and serves as a window for incoming light. The coated surface of the bulb acts as cathode. The anode is in shape of sphere.
- Photocell consists of evacuated glass tube containing two electrodes emitter (K) and collector (A).
- The emitter is shaped in the form of a semi hollow cylinder. It is always kept at a negative potential.
- The collector is in the form of a matal rod and fixed at the axis of the semi-cylinderical emitter. The collector is always kept as a positive potential.
- The glass tube is fitted on non-metallic base and pins are provided at the base for external connection.
- The emitter is connected to negative terminal and collector is connected to positive terminal of a battery.
- A radiation of frequency more than threshold frequency of material of emitter is made incident on the emitter. Photo-emissions take place. The photoelectrons are attracted towards the collector which is positive w.r.t the emitter. Thus, current flows in the circuit.
- If the intensity of incident radiation is increased, the photoelectric current increases.