A voltage applied to an `X`-ray tube being increased `eta = 1.5` times, the short-wave limit of an `X`-ray continuous spectrum shifts by `Delta lambda = 26 pm`. Find the initial voltage applied to the tube.

Explanation

The general formula is
`(2pi cancelh c)/(lambda) = eV`
Thus `lambda = (2pi cancelh c)/(eV)`
Now `Delta lambda = (2pi cancelh c)/(eV) (1-(1)/(eta))`
Hence `V = (2picancelh c)/(edelta lambda) ((eta - 1)/(eta)) = 15.9kV`