The wavelength of `K_(alpha)` line in copper is `1.54 Å`. The ionisation energy of `K` electron in copper in Joule is

Options

A. `11.2xx10^(-17)`
B. `12.9xx10^(-16)`
C. `1.7xx10^(-15)`
D. `10xx10^(-16)`

Answer

C

Explanation

For `K_(alpha)`-line, `(1)/(lamda_(alpha))=R(Z-1)^(2)((1)/(1^(2))-(1)/(2^(2)))`
`=R(Z-1)^(2)xx(3)/(4)`
`R(Z-1)^(2)=(3)/(3lamda_(alpha))`
Ionisation energy is given by
`E=Rhc(Z-1)^(2)((1)/(1^(2))-(1)/(oo))=hc(4)/(3lamda_(alpha))`
`=(6.6xx10^(-34)xx3xx10^(8)xx4)/(3xx1.54xx10^(-10))=1.7xx10^(-15)J`