Hard `X` -rays for the study of fractures in bones should have a minimum wavelength of `10^(-11) m`. The accelerating voltage for electrons in `X` -ray machine should be

Options

A. `lt124kV`
B. `gt124kV`
C. between `60 kV` and `70kV`
D. `=100kV`

Answer

a

Explanation

From conservation of energy the electron kinetic energy equals the maximum photon energy (we neglect the work function `f` because it is normally so small compared to `eV_(0)`.
`eV_(0)= hv_(max)`
or `eV_(0)=(hc)/(lambda_(min))`
`:. V_(0)=(hc)/(elambda_(min))`
or `V_(0)=(12400xx10^(-10))/(10^(-11))= 124kV`
Hence, accelerating voltage for electrons in `X`-rays machine should be less than `124kV`.