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Lithium has a work function of 2.3 eV. I...

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 = ?

Text Solution

Verified by Experts

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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