The threshold wavelength `(lambda_(0))` of sodium metal is `6500 Å`. If UV light of wavelength `360 Å` is used, what will be kinetic energy of the pho

Monjur Alahi

The threshold wavelength `(lambda_(0))` of sodium metal is `6500 Å`. If UV light of wavelength `360 Å` is used, what will be kinetic energy of the photoelectron in erge?
A. `55.175xx10^(-12)`
B. `3.056xx10^(-12)`
C. `52.119xx10^(-12)`
D. `48.66xx10^(-10)`


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Salim Ahmed Kawsar

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Correct Answer - 3
The threshold frequency `(v_(0))` corresponding to the wavelength `6500 Å` is `c//lambda_(0)`
Therefore, the threshold energy `=hv_(0)hc//lambda_(0)`
Substituting for `h, c` and `lambda_(0)` we gwt threshold energy `=3.056xx10^(-12)` ergs.
The energy of the incident photons is given by `E=hc//lambda_(0)`, since incident wavelength `lambda=360 Å`. Therefore, incident energy `=55.175xx10^(-12)` erge
The kinetic energy of the photoelectrons will be the difference of incident energy and threshold energy, `:. KE=hv-hv_(0)=(55.175xx10^(-12))-(3.056xx10^(-12))` ergs. `=52.119xx10^(-12)` ergs

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