Class 12th Physics 2017 Set1 Delhi Board Paper Solution
The work function of the following metals is given as Na = 275. eV, K = 23. eV, MO = 4 17. eV and Ni = 515. eV. Which of these metals will not cause photoelectric emission for radiation of wavelength 3300 Å from a laser source placed 1 m away from these metals? What happens if the laser source is brought nearer and placed 50 cm away?
Energy of the incident radiation of wavelength λ,
E = hc / λ
This energy of the incident radiation is greater than the work function of Na and K but less than those of Mo and Ni, so photoelectric emission will occur only in Na and K metals and not in Mo and Ni. If the laser is brought closer, the intensity of incident radiation increases. This does not affect the result regarding Mo and Ni metals, while photoelectric current from Na and K will increase in proportion to intensity.
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