Keeping all the lamps at a fixed distance. LDR and its characteristics When light is incident on it, a photon is absorbed and thereby it excites an electron from valence band into conduction band. Due to such new electrons coming up in conduction band area, the electrical resistance of the device decreases. Thus the LDR or photo-conductive transducer has the resistance which is the inverse function of radiation intensity. The band gap energy of Cadmium Sulphide is 2.
|Genre:||Health and Food|
|Published (Last):||14 December 2004|
|PDF File Size:||18.97 Mb|
|ePub File Size:||1.38 Mb|
|Price:||Free* [*Free Regsitration Required]|
Keeping all the lamps at a fixed distance. LDR and its characteristics When light is incident on it, a photon is absorbed and thereby it excites an electron from valence band into conduction band. Due to such new electrons coming up in conduction band area, the electrical resistance of the device decreases. Thus the LDR or photo-conductive transducer has the resistance which is the inverse function of radiation intensity. The band gap energy of Cadmium Sulphide is 2. Due to such large energy gaps, both the materials have extremely high resistivity at room temperature.
This resistance is typically of the order of 10 13 ohms. When light falls on it, its resistance decreases up to several kilo ohms or even hundreds of ohms, depending on the intensity of light, falling on it.
The spectral response characteristics of two commercial cells were compared in our laboratory. And we found that there is almost no response to the radiation of a wavelength which was shorter than nm. It was very interesting to note that the Cadmium Sulphide cell has a peak response nearer or within the green color of the spectrum within a range of nm. Thus it can be used nearer to the infra-red region up to nm.
It was found that the maximum response of Cadmium Sulphoselenide is in the yellow-orange range at nm and also it can be used in the infra-red region up to about nm.
In the case of a photocell, one is dealing with the relationship between the incident light and the corresponding resistance of the cell. Each photoconductor material type has its own unique spectral response curve or plot of the relative response of the photocell versus wavelength of light.
It comprises a small part of the energy radiated dEr. It varies inversely as the square of the distance. This gives the value of the current.
Investigatory Project on LDR
Softtech Computers Acknowledgement I would like to thank my chemistry teacher Mrs. Amudha for her constant guidance, motivation, moral encouragement and sympathetic attitude towards the success of this project. I also want to thank the principal and the institution for providing the necessary materials. I would also like to extend my gratitude towards the lab attendant, my parents and everyone who has helped me in completing the project successfully. It is a type of semiconductor and its conductivity changes with proportional change in the intensity of light. There are two common types of materials used to manufacture the photoconductive cells.
Investigatory Project On LDR
An opening was cut on the box to present a door. To study the variations, in current flowing in a circuit containing a LDR, because of a variation: This puts the relay switch in position-2, which cuts off the buzzer. This intruder alarm can be easily set up in houses, banks, schools etc. In the project, we use relay of 6 ohms. The kilo-ohms is connected to minimise the current flow to the battery. In project, we use 9-Volt battery. Now, the above terminal of 1.
When light falls upon it then the resistance changes. Values of the resistance of the LDR may change over many orders of magnitude the value of the resistance falling as the level of light increases. It is not uncommon for the values of resistance of an LDR or photoresistor to be several megohms in darkness and then to fall to a few hundred ohms in bright light. The sensitivity of light dependent resistors or photoresistors also varies with the wavelength of the incident light. LDRs are made from semiconductor materials to enable them to have their light sensitive properties. Many materials can be used, but one popular material for these photoresistors is cadmium sulphide, CdS.