Consider the following statements about ultraviolet (UV) rays:
(A) Most of the ultraviolet light from the sun is absorbed in the ozone layer, at an altitude of about 40–50 km.
(B) Because of their longer wavelengths, UV rays can be focussed into very narrow beams for LASIK eye surgery.
(C) UV lamps are used to kill germs in water purifiers.
(D) UV rays pass through ordinary glass, so one can get tanned through glass windows.
Which of the above statements are incorrect?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (B) and (D) only
Ultraviolet rays have shorter wavelengths than visible light, from about 400 nm down to 0.6 nm. The sun is an important source of them.
(A) Most of the ultraviolet light from the sun is absorbed in the ozone layer, at an altitude of about 40–50 km. — Correct statement. The ozone layer absorbs most of the UV from the sun and protects us from it.
(B) Because of their longer wavelengths, UV rays can be focussed into very narrow beams for LASIK eye surgery. — Incorrect statement. UV rays have shorter wavelengths than visible light. It is the short wavelength that lets them be focussed into very narrow beams.
(C) UV lamps are used to kill germs in water purifiers. — Correct statement. UV radiation kills germs, so UV lamps are used in water purifiers.
(D) UV rays pass through ordinary glass, so one can get tanned through glass windows. — Incorrect statement. Ordinary glass absorbs UV radiation. So one cannot get tanned or sunburnt through glass windows.
NCERT (2026-27):
Ultraviolet rays – “The sun is an important source of ultraviolet light. But fortunately, most of it is absorbed in the ozone layer in the atmosphere at an altitude of about 40 – 50 km.”
Ultraviolet rays – “Due to its shorter wavelengths, UV radiations can be focussed into very narrow beams for high precision applications such as LASIK (Laser-assisted in situ keratomileusis) eye surgery.”
Ultraviolet rays – “UV lamps are used to kill germs in water purifiers.”
Ultraviolet rays – “UV radiation is absorbed by ordinary glass. Hence, one cannot get tanned or sunburn through glass windows.”