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Monochromatic light ofwavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW. a. Find the energyand momentum of each photon is the light beam. b. How many photons per second, on the average, arrive at a target irradiated by this beam? (Assume the beam to have uniform cross-section which is less than the target area). c. How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon? |
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Answer» Solution :`LAMBDA=632.8 nm=632.8xx10^(-9)m, P=9.42 mW=9.42xx10^(-3)W` a.`E=hupsilon=h(C )/(lambda)=(6.6xx10^(-34)xx3xx10^(8))/(632.8xx10^(-9))=3.14xx10^(-19)J=1.96eV` `p=(h)/(lambda)=(6.6xx10^(-34))/(632xx10^(-9))=1.044xx10^(-27) KG ms^(-1)` B. `P=nh upsilon, n=(P)/(h upsilon)=(Plambda)/(hc)=(9.42xx10^(-3)xx632.8xx10^(-9))/(6.6xx10^(-34)xx3xx10^(8))=3xx10^(16)` photon/s c.`mv=1.044xx10^(-27), v=(1.044xx10^(-27))/(1.67xx10^(-27))=0.625m//s` |
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