A #200 W# power source emits monochromatic light of wavelength #4950 Angstrom#. How many photons per minute are emitted by the source? [Given: #h = 6.6 xx 10^-34 Js#]

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Answer 1 · 2017-03-22T09:22:59

The number of photons #=3*10^22#

Energy of 1 photon is

#E=h nu=h c/lambda#

#c=2.998 *10^8ms^-1#

#1 Angstrom =10^-10m#

#4950 Angstrom =4950*10^-10=4.95*10^-7#

#E_1=6.6*10^-34*2.998 *10^8*1/(4.95*10^-7)#

#=6.6*2.998/4.95*10^-19J#

#=3.997*10^-19J#

Energy, power and time are related by

#E=P*t#

#E=200*60=12000J#

Number of photons #=n#

#n*E_1=E#

#n=E/E_1=1.2*10^4/(3.997*10^-19)#

#=1.2/3.997*10^23#

#=0.3*10^23# photons