Which of the following radiation is used to get relief from body aches ?

Question

UnlockIAS · Accepted Answer

Correct — A, Infra-red radiation. Infrared occupies the band of the electromagnetic spectrum just beyond the red end of visible light, from roughly 700 nanometres to about a millimetre in wavelength, and its defining practical property is that biological tissue absorbs it and converts it directly into heat. An infrared lamp directed at a shoulder or a knee raises the temperature of the tissue a few millimetres below the skin; the local blood vessels dilate in response, blood flow to the area increases, muscle tone relaxes and the perception of pain falls. That is the entire basis of the infrared lamp used in physiotherapy departments, and of every heat pad and hot-water bottle applied to a sore back — infrared is simply the radiant version of the same therapy. The reason it is infrared and not one of the neighbouring bands is a matter of photon energy. Photon energy rises as wavelength falls, so infrared photons are too weak to break chemical bonds and can only set molecules vibrating, which is what heat is. Ultraviolet photons are energetic enough to damage DNA, which is why UV is used to kill microorganisms rather than to soothe muscles. Visible light lies between the two and passes through or scatters off tissue without depositing a useful amount of heat. Since option (a) is a real and standard clinical use, 'None of these' cannot stand.

Why the other options are wrong — (b) Ultraviolet has genuine medical uses, which is precisely why it is the tempting wrong answer — it sterilises water, air and instruments because its photons damage microbial DNA, and UV-B on the skin drives the synthesis of vitamin D. Neither is analgesia. In dose it is harmful, causing sunburn, cataract and skin cancer, and no one treats a sore muscle with it.  (c) Visible light, from about 400 to 700 nanometres, carries too little energy to affect molecular bonds and too little absorbed heat to warm tissue usefully; it is largely scattered or reflected at the skin. Its medical roles are in imaging, endoscopy and phototherapy for neonatal jaundice, not in pain relief.  (d) Available only if all three named bands failed, and one of them plainly does not — the infrared lamp is standard physiotherapy equipment. Treat a 'None of these' option the way you would treat any universal claim: it requires every other option to be false, so a single confirmed true option destroys it.

Concept: The electromagnetic spectrum runs, in order of increasing wavelength and decreasing photon energy, from gamma rays and X-rays through ultraviolet, visible light and infrared to microwaves and radio waves. All travel at the speed of light in vacuum and differ only in wavelength and frequency, but that one difference determines everything about how each interacts with matter, and therefore what each is used for. The high-energy end is ionising: gamma rays and X-rays can knock electrons out of atoms and break DNA, which makes them both dangerous and useful — X-rays for imaging, cobalt-60 gamma rays for radiotherapy and sterilisation. Ultraviolet sits at the boundary, energetic enough to damage biological molecules but not to penetrate deeply. Infrared is absorbed as vibrational energy, that is, as heat. Microwaves excite water molecules, which is why they cook food. Radio waves pass through most matter and carry communication. Infrared was the first band to be discovered beyond the visible: William Herschel found it in 1800 by placing a thermometer just beyond the red edge of a prism's spectrum and observing that it registered the highest temperature of all.

State PCS 2024 Q88 — Science & Technology PYQ with Answer

State PCS 2024 Q88 — Science & Technology PYQ with Answer