X-Rays - 6

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

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

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

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

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

(JEE 2008)

Answer (B)

Reason:m (λc) cuttoff wavelength is given as
λc = hc/K.E. = hc/eV

Hence λc does not depend on atomic number of target but depends on potential difference between cathode and anode (target)

X-Rays - 7

1. The shortest wavelength of x-rays emitted from an x-ray tube depends on

a. current in the tube
b. the voltage applied to the tube
c. the nature of gas in the tube
d. the atomic number of the target material

More than one alternative possible

(JEE 1982)

answer: (b)

The wave length of emitted X-rays depends on the voltage applied to the x-ray tube.

2. To produce characteristic X-rays using a tungsten target in an X-ray generator, the accelerating voltage should be greater than ---------------- volts and the energy of the characteristic radiation is ---------------- eV.
(The binding energy of the innermost electron in tungsten is 40 KeV)

(JEE 1983)

answer: 40 kilo volts, 40 KeV

Energy of the accelerating electron should be equal to the binding energy of the electron in tungsten

Hence E = eV = 40 keV
 V = 40 kV

Energy of the characteristic radiation is equal to the characteristic kinetic energy of bombarding electrons.

3. A potential difference applied to an X-ray tube is increased. As a result, in the emitted radiation

a. the intensity increases
b. the minimum wave length increases
c. the intensity remains unchanged
d. the minimum wave length decreases


Answer: (d)

(JEE 1988)

λ_min = hc/eV
If V is increased, minimum wave length will decrease