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The work function for the following meta...

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? What happens if the laser is brought nearer and placed 50 cm away?

Text Solution

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Here, `lamda=3300A=3300xx10^(-10)`
Therefore, energy of a photon of incident light,
`E=(hc)/(lamda)=(6.62xx10^(-34)xx3xx10^8)/(3.300xx10^(-10))`
`=6.018xx10^(-19)=(6.018xx10^(-19))/(1.6xx10^(-19))=3.76eV`
Since the work function of Mo and Ni are greater than the energy of the photon of oncident light, photoelectric emission will not occur for these metals.
If the laser is brought nearer, the intensity of incident radiation on the metals will increase. It will increase the photoemission in case of Na and K. However, No photoelectric emission will take place in case of Mo and Ni.
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