1.

A photon of wavelength `4xx 10^(-7)` m strikes on metal surface, the work function of the metal being 2.13 eV. Calculate (i) the energy of the photon (eV) (ii) the kinetic energy of the emission and (iii) the velocity of the photoelectron `(1 eV = 1.602 xx 10^(-19) J)`

Answer» (i) Energy of the photon `(E) = hv = (hc)/(lamda) = ((6.626 xx 10^(-34) Js) xx(3 xx 10^(8) ms^(-1)))/(4 xx 10^(-7) m) = 4.97 xx 10^(-19) J`
`= (4.97 xx 10^(-19))/(1.602 xx 10^(-19)) eV = 3.10 eV`
(ii) Kinetic energy of emission `((1)/(2) mv^(2)) = hv - hv_(0) = 3.10 - 2.13 = 0.97 eV`
(iii) `(1)/(2) mv^(2) = 0.97 eV = 0.97 xx 1.602 xx 10^(-19) J`
i.e., `(1)/(2) xx (9.11 xx 10^(-31) kg) xx v^(2) = 0.97 xx 1.602 xx 10^(-19) J`
or `v^(2) = 0.341 xx 10^(12) = 34.1 xx 10^(10) or v = 5.84 xx 10^(5) ms^(-1)`


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