Question

The maximum wavelength for which an em wave can ejected electrons form a platinum surface is 195 nm. When radiations with a wavelength of 131nm shines on the surface. What is the maximum speed of the ejected electrons? [Use `h=6.63xx10^(-34)Js`] `m_(e)=9.1xx10^(-31)kg`.

Answer 1

Correct Answer - `.105xx10^(6)ms^(-1)`
Here, `lambda_(0)=195nm=195xx10^(-9)m`,
`lambda=131xx10^(-9)m`
`1/2mv_(max)^(2)=(hc)/lambda-(hc)/(lambda_(0))`
`=(6.63xx10^(-34)xx3xx10^(8))/(131xx10^(-9))-(6.63xx10^(-34)xx3xx10^(8))/(195xx10^(-9))`
`=0.152xx10^(-17)-0.102xx10^(-17)J`
`v_(max)=[2/mxx0.050xx10^(-17)]^(1//2)`
`=[2/(9.1xx10^(-31))xx0.050xx10^(-17)]^(1//2)`
`=1.05xx10^(6)ms^(-1)`