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A hypothetical atom has two energy levels, with a transition wavelength between them of . In a particular sample at 300 K,4.01020such atoms are in a state of lower energy. (a) How many atoms are in the upper state, assuming conditions of thermal equilibrium? (b) Suppose, instead, that3.0x1020 of these atoms are 鈥減umped鈥 into the upper state by an external process, with1.01020 atoms remaining in the lower state. What is the maximum energy that could be released by the atoms in a single laser pulse if each atom jumps once between those two states (either via absorption or via stimulated emission)?

Short Answer

Expert verified

(a) The number of atoms in the upper level assuming conditions of thermal equilibrium is 0.

(b) The maximum energy that could be released by the atoms in a single laser pulse is 68 J.

Step by step solution

01

The given data:

The wavelength of the transition between the energy levels,=580nm

The temperature of the sample, T =300 K

The number of atoms in the lower state without external process, N1=41020atoms

The number of atoms in the upper state with external process or number of the emitting photons,N1=31020atoms

The number of atoms in the lower state without external process or the atoms absorbing photons,

N2=11020atoms

Consider the known data below.

The Plank鈥檚 constant is,

h=6.6310-34J.s=6.24210186.6310-34eV.s=41.38410-16eV.s

The speed of light is,

c=3108m/s=3108109nm/s=31017nm/s

02

Understanding the concept of the Boltzmann distribution equation

The law states that the chances of a molecule gaining energy decreases with increasing energy equal to the Boltzmann factor exp(-/kT).

Photon energy is the energy carried by a single photon. The amount of energy is directly proportional to the magnetic frequency of the photon and thus, equally, equates to the wavelength of the wave. When the frequency of photons is high, its potential is high.

Using the Boltzmann-distribution equation which is the expression for the probability for stimulated emission of radiation to the probability for spontaneous emission of radiation under thermal equilibrium, we can get the number of photons present in the upper energy level. Again, using the same relation with Planck's equation, the maximum energy can be calculated.

Formula:

The Boltzmann energy distribution equation,

N1N2=e-E2-E1/kT 鈥.. (1)

Here, the Boltzmann constant is,k=1.3810-23J/K

The energy of the photon due to Planck鈥檚 relation,

E=hc 鈥.. (2)

03

(a) Calculation of the number of photons present in the upper energy level

Using the given data and equation (2) in equation (1) before any application of an external process, the value of the number of photons present in the upper energy level of the transition is as follows.

N1=N2e-hc/位办罢=41020exp41.38410-16eV.s31017nm/s580nm8.6210-5eV/K300K=510-161Caseisnotpossible

Hence, there are no electrons in the upper energy level.

04

(b) Calculation of the maximum energy released by the atoms in a single laser pulse:

With the application of the external process, the net output energy considering the number of photons and energy relation can be given energy of photon from equation (2) as follows.

E=N1-N2hc=31020-110206.6310-34J.s3108m/s58010-9m=68J

Hence, the value of the maximum energy is 68 J.

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