Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Absorption of radiation
If an atom is initially in a lower state 1, it can rise to a higher stare 2 by absorbing a quantum of radiation. Photon of frequency v where E1 and E2 are the atom in the states 1 and 2 respectively. The process is known as absorption of radiation. The probable rate of this transition 1of 2 depends on the properties of stares 1 and 2 and is proportional to the energy density of the radiation of frequency v incident on the atoms. Thus P12 = B12 u (v) where B12 is proportionality constant and is known as Einstein coefficient of absorption of radiation.
Spontaneous emission Let rs now consider an atom initially in the higher state 2. Excited state with higher energy is inherently unstable, and atom in excited stste does not stay for longer time and jumps to the lower energy state 1 emitting a photon of frequency v. This is spontaneous emission of radiation. If there is an assembly of atoms, the radiation emitted spontaneously by each atom has a random direction and a random phase and is therefore incoherent from one atom to another. The probability of spontaneous emission is determined only by the properties of states 2 and 1. This is denoted by A21 which is known as Einstein coefficient of spontaneous emission of radiation. In this case the probability of spontaneous emission is independent of it.
Stimulated Emission According to Einstein, an atom in an excited energy state may, under the influence of the electromagnetic field of a photon of frequency v incident upon it jumps to a lower energy state, emiting an additional photon of same-frequency (v) (fig). Hence tow photons, one original and the other emitted move together. This is stimulated emission of radiation. The direction of propagation, phase, energy and state of polarization of the emitted photon is exactly same as that of the incident stimulating photon, so the result is an enhanced beam of coherent light. The probability of stimulated emission transition 2 - 1 is proportiaonl to the energy density of the stimulating radiation and is given by B21 u (v) where B21 is the Einstein coefficient of stimulated emission of radiation. The total probability for an atom in state 2 to drop to the lower state 1 is therefore P21 = A21 + B21 u (v).
Relation between Einstein's coefficient When a steady state is reached, there should be a balance between the absorption and emission processes. Hence under this situation, number of atoms absorbing radiation per unit time must be equal to the number of atoms emitting radiation per unit time so that the number of atoms in any energy level does not change with time.
Q. Athree-phase, 60-Hz transmission line has a total series impedance of 22.86 62.3° per phase. It delivers 2.5 MW at 13.8 kV to a load connected to its receiving end. Compute th
Q . Materials that can store electrical energy are called (A) magnetic materials. (B) semi conductors. (C) dielectric materials. (D) super conductors. Ans: C
HOW DOES SINGLE PHASE INDUCTION MOTORS DEVELOP A STARTING TORQUE ?
Explain Register Direct and Indirect data addressing mode (with examples) available in microprocessors. Register Direct Modes and Register Indirect Modes: Does not giv
Q. Two charges of equal magnitude 5µC but opposite sign are separated by a distance of 10 m. Find the net force experienced by a positive charge q = 2 µC that is placed midway betw
The IC engine based automobiles have been built and sold for more than 100 years. Predominantly the fuels used for running these IC engines have been petrol and diesel. In recent t
The advantage of the analog storage oscilloscope is that it has higher bandwidth and writing speed than a digital oscilloscope, being capable of operating speeds of about 15 GHz. T
Simplified operation: Figure: Simple circuit to show the labels of a bipolar transistor. The essential value of a transistor comes from its capability to make use
what is fuck
I´m looking for some help to identify some electronic parts, i have this led driver with preset dim levels that i can reach with switching the power on and off. The driver worked r
Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!
whatsapp: +1-415-670-9521
Phone: +1-415-670-9521
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd