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The work function for the following metals is given: Na: 2.75 eV; K: 2.30 eV; Mo: 4.17 eV; Ni: 5.15 eV. Which of these metals will not give photoelectric emission for a radiation of wavelength 3300 Å from a He-Cd laser placed 1 m away from the photocell?

Q: 11.29  The work function for the following metals is given:                                                                                           Na:2.75\hspace{1mm}eV,K:2.30\hspace{1mm}eV,Mo:4.17\hspace{1mm}eV,Ni:5.15\hspace{1mm}eV. 

Which of these metals will not give photoelectric emission for a radiation of wavelength 3300\hspace{1mm}\dot{A} from a He-Cd   laser placed 1\hspace{1mm}m away from the photocell? What happens if the laser is brought nearer and placed 50\hspace{1mm}cm away? 

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S Sayak

The wavelength of the incident photons=3300\dot{A}

The energy of the incident photons is

\\E=\frac{hc}{\lambda }\\ E=\frac{6.62\times 10^{-34}\times 3\times 10^{8}}{3300\times 10^{-10}\times 1.6\times 10^{-19}}\\ E=3.16 eV

Mo and Ni will not give photoelectric emission for radiation of wavelength 3300\hspace{1mm}\dot{A} from a He-Cd.

If the laser is brought nearer no change will be there in case of Mo and Ni although there will be more photoelectrons in case of Na and K.

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