Arrange the given associated wavelengths (\( \lambda_1, \lambda_2, \lambda_3 \) and \( \lambda_4 \)) of radiations with the part of the electromagnetic spectrum in decreasing order of magnitude:
(A) \( \lambda_1 \) used to detect fracture in bones
(B) \( \lambda_2 \) used to kill germs in water purifiers
(C) \( \lambda_3 \) used to treat muscular strain
(D) \( \lambda_4 \) used to transmit voice communication
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (D), (C), (B), (A)
Identify the radiation used in each case and place it in the electromagnetic spectrum.
(A) \( \lambda_1 \) used to detect fracture in bones — X-rays, \( \lambda \sim 10^{-10}\,\mathrm{m} \)
(B) \( \lambda_2 \) used to kill germs in water purifiers — ultraviolet, \( \lambda \sim 10^{-8}\text{ to }10^{-7}\,\mathrm{m} \)
(C) \( \lambda_3 \) used to treat muscular strain — infrared, \( \lambda \sim 10^{-6}\text{ to }10^{-4}\,\mathrm{m} \)
(D) \( \lambda_4 \) used to transmit voice communication — radio waves, \( \lambda \gt 0.1\,\mathrm{m} \)
The wavelength is largest for radio waves, then infrared, then ultraviolet and smallest for X-rays.
\( \displaystyle \lambda_{4}\,(\mathrm{D}) \gt \lambda_{3}\,(\mathrm{C}) \gt \lambda_{2}\,(\mathrm{B}) \gt \lambda_{1}\,(\mathrm{A}) \)
The decreasing order is (D), (C), (B), (A).
NCERT (2026-27):
Electromagnetic Spectrum – “… We briefly describe these different types of electromagnetic waves, in order of decreasing wavelengths.”
Radio Waves – “… Cellular phones use radio waves to transmit voice communication in the ultrahigh frequency (UHF) band.”
Infrared Waves – “… Infrared lamps are used in physical therapy.”
Ultraviolet Rays – “… UV lamps are used to kill germs in water purifiers.”
X-Rays – “… X-rays are used as a diagnostic tool in medicine and as a treatment for certain forms of cancer.”