The X ray spectrum in the diagram has two curves each representing a different accelerating voltage.

Each spectrum has two parts:
(a) a continuous background
(b) a series of sharp peaks.

The background is due to radiation emitted as the electrons are slowed down by electromagnetic attraction of the nuclei of the material.
The rest of the curve is produced by electrons losing only part of their energy during collisions with many nuclei.

where V is the accelerating voltage and c the velocity of light.
The smaller the value of V, the greater the minimum wavelength will be and the smaller the maximum frequency.
The peaks on the spectrum are characteristic of the particular target material.