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if the surface of a metal is successfully exposed to rediation of `lamda _(1)=350 nm and lamda_(2)=450` nm th miximum velocity velocity of protoelectrons will differ by a factor 2 . The work function of this metal is :A. `2.84xx10^(-19)J`B. `1.6xx10^(-19)J`C. `3.93xx10^(-19)J`D. `2.4xx10^(-19)J` |
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Answer» Correct Answer - C from photo electric `eq^(n)`: `(hc)/(lamda_(1))=W_(0)+(mV_(1)^(2))/(2)" "...(1)` `and (hc)/(lamda_(2))=W_(0)+(mV_(2)^(2))/(2)" "...(2) ` `from (1)-(2) hc((1)/(lamda_(1))=(1)/(lamda_(2)))=(m)/(2) (V_(1)^(2)-V_(2)^(2))` `(m)/(2)(4V_(2)^(2)-V_(2)^(2))` `=(3mV_(2)^(2))/(2)` `therefore (mV_(2)^(2))/(2)=(hc)/(3)[(1)/(lamda_(1))-(1)/(lamda_(2))]" "...(3)` from (2 ) and (3) `W=-(he)/(3)[(1)/(lamda_(1))-(4)/(lamda_(2))]` `=3.93xx10^(-19)J` |
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