Class 12 Physics Chapter 18 Notes

• Important physics class 12 chapter 18 mcqs for Intermediate part-I students.
• A brief review of P-N junction and its characteristics
• Forward biased by P-N junction and reverse Biased P-N junction
• Important ch 18 physics class 12 notes for Intermediate part-I students.
• Rectification with its type half wave rectification full wave rectification
• Specially designed P-N junctions
• Light emitting diode, photodiode, photo voltaic cell
• Important chapter 18 physics class 12 mcqs for Intermediate part-I students.
• Transistors and current flow in a n-p-n Transistor
• Transistor as an amplifier
• Transistor as a switch and operational amplifier
• Important chapter 18 physics class 12 for Intermediate part-I students.
• Characteristics of input resistance, output resistance, open loop gain
• OP-AMP as Inverting amplifier
• OP-AMP as a Non-Inverting amplifier
• OP-AMP as a comparator
• Important Class 12 Physics chapter 18 Important numericals for Intermediate part-I students.
• Comparator as a night Switch and Digital systems
• Fundamental logic gates (i) OR gate  (ii) and Gate  (iii) Not gate
• Other logic gates and nor Gate, NAND gate, exclusive OR gate (XOR ), and Exclusive- NOR gate (XNOR)
• Applications of gates in control systems
• Important Class 12 Physics chapter 18 notes handwritten for Intermediate part-I students.
• Reverse biased P-N junction: When the external source of voltage is applied across a p-n junction such that its positive terminal is connected to n-region and its negative terminal to p-region the p-n junction is said to be reverse biased. In this situation no current flows due to the majority charge carries. However a very small current, of the order of few microamperes flows across the junction due to flow of minority charge carriers. It is known as reverse current or leakage current. The variation of reverse current with the applied bias voltage can be studied by the circuit.
• Important chapter 18 physics class 12 notes for Intermediate part-I students.
• The reverse characteristic for the p-n junction. It can be seen that as the reverse voltage is increased from 0, the reverse current quickly rises to its saturation value l0. As the reverse voltage is further increased, the reverse current remains almost constant. Here the resistance offered by the diode is very high of the order of several mega ohms.
• Important chapter 18 physics class 12 notes for Intermediate part-I students.
• As the reverse voltage is increased, the kinetic energy of the minority charge carriers with which they cross the depletion region also increases till it is sufficient to break a covalent bond. As the covalent bond breaks, more electron-hole pairs are created. Thus, minority charge carriers begin to multiply due to which the reverse current begin to increase till a point is reached when the junction breaks down and reverse current rises sharply. After breakdown the reverse current will rise to very high value which will damage the junction.
• Important chapter 18 physics class 12 short questions for Intermediate part-I students.
• Rectification: Conversion of alternating current into direct current is called rectification. Semi-conductor diodes are extensively used for this purpose. There are two very common types of rectification. (i) Half-wave rectification and (ii) Full-wave rectification.
• Important chapter 18 physics class 12 short questions for Intermediate part-I students.
• Specially designed P-N junction: In addition to the use of semi-conductor diode as rectifier, many types of p-n junctions have been developed for special pirocses. Three most commonly used such diodes are: 
• (i) Light emitting diode (ii) Photodiode (iii) Photo voltaic cell
• Important Class 12 Physics chapter 18 notes for Intermediate part-I students.
• (i) Light emitting diode: Light emitting diodes ( LED ) are made from special semi-conductors such as gallium arsenide and gallium arsenide phosphide in which the potential barrier between p and n sides is such that when an electron combines with a hole during forward bias conduction, a photon of visible light is emitted. These diodes are commonly used as small light sources. A specially formed array of seven LED'S is used for displaying digits etc.. in electronic appliances.
• Important chapter 18 physics class 12 long questions for Intermediate part-I students.
• (ii) Photodiode: Photo diode is used for the detection of light It is operated in the reverse biased condition. When no light is incident on the junction, the reverse current I is almost negligible but when its p-n junction is exposed to light, the reverse current increases with the intensity of light. A photo diode can turn its current ON and OFF in nano-seconds. Hence it is one of the fastest photo detection devices. Applications of photo diode include.
• Important ch 2 physics class 18 solutions for Intermediate part-I students.
• Total Page  = 53 pages
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