Given:

Let

λ be the cut off wavelength and V be the operating potential in the X-ray tube.
Then,

Here,
h = Planck’s constant
c = Speed of light

If the operating voltage is increased by 1%, then the new operating voltage will be given by

V’=V+1/100×V= 1.01

V Cut-off wavelength on increasing the operating voltage is given by

difference in wavelength =

Percentage change in the wavelength is given by

=11.01=0.9901 = 1% (approx.)