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A. How many photons of a tradiation of wavelength `lamda=5xx10^(-7)` m must fall per second on a blackened plate in order to produce a force of `6.62xx10^(-5)`N? B. At what rate will the temperature of plate rise if its mass is 19.86kg and specific heat is equal to `2500J(kgK^(-1))`?A. `3xx10^(19)`B. `5xx10^(22)`C. `2xx10^(22)`D. `1.67xx10^(18)` |
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Answer» Correct Answer - B The momentum of photon `=(h)/(lamda)` If n is the number of photons falling per second on the plate, then total momentum per second of the incident photons is `P=nxx(h)/(lamda)` Since the plate is blackened, all photons are absorbed by it. `(triangleP)/(trianglet)=n(h)/(lamda)` Since `F=(triangleP)/(trianglet)=n(h)/(lamda)` `n=(Flamda)/(h)` `=(6.62xx10^(-5)xx5xx10^(-7))/(6.62xx10^(-34))=5xx10^(22)` |
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