IIT-JEE 2008 · Paper 1 · Physics Q26

PhysicsSingle correct+3 / -1Question 26 of 69

Which one of the following statements is WRONG in the context of X-rays generated from a X-ray tube?

Wavelength of characteristic X-rays decreases when the atomic number of the target increases

Cut-off wavelength of the continuous X-rays depends on the atomic number of the target

Intensity of the characteristic X-rays depends on the electrical power given to the X-ray tube

Cut-off wavelength of the continuous X-rays depends on the energy of the electrons in the X-ray tube

Answer and worked solution

Official answer: B

(A) Characteristic lines follow Moseley's law, $\frac1\lambda\propto(Z-1)^2$ : heavier targets give shorter wavelengths. Correct.
(B) The cut-off wavelength is $\lambda_\text{min}=\dfrac{hc}{eV}$ , set by the accelerating voltage alone, independent of the target. Wrong.
(C) More power (more electrons per second) gives more intense lines. Correct.
(D) The cut-off depends on the electrons' energy $eV$ . Correct.

(B)

Topics:X-rays Moseley's law

IIT-JEE 2008 · Paper 1, Physics question 26