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Monochromatic light of frequency \(6.0\times 10^{14}Hz\)  is produced by a laser. The power emitted is \(2.0\times 10^{-3}W\)  
(a) What is the energy of a photon in the light beam?
(b) How many photons per second, on an average, are emitted by the source?
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PhysicsClass 12

Monochromatic light of frequency \(6.0\times 10^{14}Hz\)  is produced by a laser. The power emitted is \(2.0\times 10^{-3}W\)  
(a) What is the energy of a photon in the light beam?
(b) How many photons per second, on an average, are emitted by the source?

Answer

(a) Frequency of monochromatic light, \(v=6.0\times 10^{14}Hz\)
Energy of a photon is given by;
\(E=\mathit{hv}\)
\(=6.62\times 10^{-34}\times 6.0\times 10^{14}\)
\(=3.98\times 10^{-19}\)
(b) Consider the number of photons emitted per second to be, \(N\).
And power emitted is, . \(P=2.0\times 10^{-3}\) \(W\)
Power transmitted in the beam equals Answer for Monochromatic light of frequency 6.0times 10^{14}Hz  is produced by a laser. The power emitted is 2.0times 10^{-3}W  (a) What is the energy of a photon in the light beam? (b) How many photons per second, on an average, are emitted by the source?times the energy per photon;
\(P=\mathit{NE}\)
\(N=\frac P E\)
\(N=\frac{2.0\times 10^{-3}}{3.98\times 10^{-19}}=5.0\times 10^{15}\)  photons per second
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