Question

Cutoff wavelength of X-rays coming from a Coolidge tube depends on the
(a) target material
(b) accelerating voltage
(c) separation between the target and the filament
(d) temperature of the filament.

Answer 1

(b) accelerating voltage

Cutoff wavelength $\left({\lambda }_{\min }\right)$ is given by
${\lambda }_{\min }=\frac{hc}{eV}$
Here,
h = Planck's constant
c = Speed of light
V = Accelerating voltage
e = Charge of electron
Clearly, a cutoff wavelength depends on accelerating voltage. It does not depend on the target material, separation between the target and the temperature of the filament.