LDR (Light dependent resistor)

LDR 

LDR is electronic device, which is widely used in electronic science and engineering we can say that it is like a register it does consists some resistance. The full form of LDR is light dependent resistor it work on the principle of photoconductivity photo means light and conductivity means flow of electron heat through it. Other words we can say that it is based on photo register that means when the number of light ray increases then the resistance of LDR will be decreases.

 

LDR (Light dependent resistor)

For  LDR , incident light intensity is always inversely proportional to the resistance.
                                                 Light Intensity ∝ 1/Resistance (LDR)

 A proportional relationship is one in which two quantities vary directly with each other. We say the variable y varies directly as x if: y=kx. for some constant k , called the constant of proportionality .

A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, for example, silicon. In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (that is, longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. It is an example of an extrinsic semiconductor. It is made by semiconductor. It does more resistance megaohms (Mohms) when the light incident on the surface of LDR then some resistance does decrease hindered ohms incident light on LDR greater than threshold frequency or a certain frequency semiconductor absorbed the photos which are given by visible light. It is enough to electron jumps into the conduction band. So the free electrons conduct electricity because LDR some resistan does decrease.