An electric bulb of 100 Watts converts 3% electrical energy into light energy. If the wavelength of light emitted is 6625 A, the number of photons emitted in 1 s is? h= 6.625 x 10^-34 J.sec
Correct answer: B. 1019
- A. 1017
- B. 1019
- C. 1021
- D. 1015
Explanation
P=100 x 3 / 100= 3 Watts λ=6625 A= 6625x 10^-10 m P=Nhc/λt N=Pλt/hc 3 x 6625 x 10^-16 x 1 / 6.625x10^-34 x 3 x 10^9 N=10^19
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About Dawn of Modern Physics
Classical physics cannot explain blackbody radiation and related observations, leading to Planck’s quantum theory, in which energy is emitted or absorbed in discrete packets. Photons provide the particle model of light, with energy and momentum linked to frequency and wavelength, including the photoelectric effect and its threshold frequency.
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