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InterviewSolution
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The work function for the following metals is given: Na:2.75eV,K:2.30eV,Mo:4.17eV,Ni:5.15eV. 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 ? |
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Answer» Solution :Here `lamda=3300Å=3300xx10^(-10)m=3.3xx10^(-17)m` `therefore`Energy of radiation photon in eV `E=(hc)/(elamda) eV=(6.63xx10^(-34)x3xx10^(8))/(1.6xx10^(-19)xx3.3xx10^(-7))eV=3.767eV` For photoelectric emission energy of radiation photon must be greater than or equal to the work function of given metal. therefore, we conclude that in present CASE photoelectric emission from NA and K is possible but from Mo and Ni no photoelectric emission will take place. There is no effect on photoelectric emission from Mo and Ni even when laser source is brought nearer to the PHOTOCELL. HOWEVER, on bringing the source nearer, the intensity of radiation increases. As a result, in case of Na and K, the value of photoelectric current will rise in proportion to the rise in intensity of radiation. |
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