Moseley's Law - Practice Questions & MCQ

Moseley's Law-

During the time when the periodic table is arranged with atomic weight, Moseley measured the frequency of charcterstic X-rays from a large number of elements and plotted the square root of the frequency against its position number in the periodic table. He discovered that the plot is very close to a straight line. A portion of Moseley's plot is shown in figure where $\sqrt{\nu}$ of $\mathrm{K}_\alpha \mathrm{X}$-rays is plotted against the position number. From this linear relation, Moseley concluded that there must be a fundamental property of the atom which increases by regular steps as one moves from one element to the other. This quantity was later identified to be the number of protons in the nucleus and was referred to as the atomic number.

The frequency $\nu$ of a characteristic X-ray of an element is related to its atomic number $Z$ by

$$
\sqrt{\nu}=a(Z-b)
$$

where a and b are constants called proportionality and screening (or shielding) constants. For K series, $a=\sqrt{\frac{3 R c}{4}}$ and that of b is 1 . Here R is Rydberg's constant and c is speed of light (as in Bohr's model).