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Lithium has a work function of 2.3 eV. It is exposed to light of wavelength 4.8 xx 10^(-7) m. Find the maximum kinetic energy with which the electron leaves the surface. What is the longest wave length which can produce the photo electrons ? Data : W = 2.3 eV, h=6.626 xx 10^(-34)Js, e=1.6 xx 10^(-19)C. Longest wavelength = ? , Kinetic energy = ? |
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Answer» Solution :Kinetic energy of ejected ELECTRON = hv-W But,`hv=(hc)/(lambda)` `=(6.26 xx 10^(-34) xx 3 xx 10^(8))/(4.8 xx 10^(-7))`JOULE `hv=(6.626 xx 10^(-34)xx3xx10^(8))/(4.8xx10^(-7)xx1.6xx10^(-19))` hv = 2.588eV `:.` Kinetic energy of ejected electrons = 2.588-2.3 KE = 0.288 eV Work function,`W=hv_(0)=(hc)/(lambda_(0))` `:. lambda_(0)=(hc)/(W)` LONGEST wavelength `lambda_(0)=(6.626xx10^(-34)xx3xx10^(8))/(2.3xx1.6xx10^(-19))` `lambda_(0)=5.40xx10^(-7)m`. |
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