Question

Given below are some famous numbers associated with electromagnetic radiations in different contexts in physics. State the part of the electromagnetic spectrum to which each belongs.

(a) 21 cm (wavelength emitted by atomic hydrogen in interstellar space).

(b) 1057 MHz (frequency of radiation arising from two close energy levels in hydrogen; known as Lamb shift).

(c) 2.7 K [temperature associated with the isotropic radiation filling all space thought to be a relic of the big-bang origin of the universe].

(d) $5890\mathring{A}-5896\mathring{A}$ [double lines of sodium]

(e) 14.4 ke V [energy of a particular transition in ${}^{57}$Fe nucleus associated with a famous high resolution spectroscopic method ($\text{M}\ddot{o}\text{ssbauer spectroscopy}$)].

Answer 1

(a)

Radio waves have wavelengths of 1mm to 100km. Hence, 21cm lies at short wavelength end of radio waves.

(b)

Radio waves belong to the shortest wavelength in the electromagnetic spectrum.

(c)

${\lambda }_m=0.29/T=0.11cm$

This wavelength corresponds to the microwaves.

(d)

Lines from 400nm to 700nm lies in visible range. The range of 589nm lies in Yellow part of visible spectrum.

(e)

$E=h\nu$

$\nu =3.4\times {10}^{18}Hz$

This corresponds to the X-rays.