NCERT Class XII Chapter
Electromagnetic Waves
Questions With Solutions
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Question : 14
Total: 15
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 Å – 5896 Å [double lines of sodium]
(e) 14.4 keV [energy of a particular transition in
F e
(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 Å – 5896 Å [double lines of sodium]
(e) 14.4 keV [energy of a particular transition in
Solution:
(a) 21 cm wavelength corresponds to radiowaves, at nearly 1445 MHz.
(b) Electromagnetic wave of 1057 MHz also corresponds to radiowaves.
(c) Using Wien’s Law the wavelength of the radiation mostly emitted at given temperature of heavenly bodies can be calculated
λ m T
orλ m
This wavelength corresponds to microwave region of electromagnetic waves.
(d) This wavelength corresponds to visible region (yellow) of electromagnetic waves.
(e) The frequency of radiation can be calculated, E = hυ
v =
10 18
This frequency corresponds to X-ray region of electromagnetic waves.
(b) Electromagnetic wave of 1057 MHz also corresponds to radiowaves.
(c) Using Wien’s Law the wavelength of the radiation mostly emitted at given temperature of heavenly bodies can be calculated
or
This wavelength corresponds to microwave region of electromagnetic waves.
(d) This wavelength corresponds to visible region (yellow) of electromagnetic waves.
(e) The frequency of radiation can be calculated, E = hυ
v =
This frequency corresponds to X-ray region of electromagnetic waves.
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