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UPSC Prelims 1993 · Environment · Pollution Files
When there is depletion of ozone in the stratosphere, the wavelength of radiation striking the earth's surface will be
- (a) 10⁻⁷ m
- (b) 10⁻¹⁰ m
- (c) 10⁻² m
- (d) 10⁰ m
Show the answer and explanation
Answer: (a) 10⁻⁷ m
10⁻⁷ m is the order of magnitude for ultraviolet; ozone thinning mainly increases UV-B (280–315 nm) at the ground.
The idea
Arrange radiation by wavelength, from shortest to longest. The ozone layer absorbs ultraviolet rays, so if it thins, the extra radiation reaching the ground is mainly UV-B, with wavelengths of about 280–315 nm.
X-rays: about 10⁻¹⁰ m → Ultraviolet: about 10⁻⁷ m → Visible light: 4 to 7 × 10⁻⁷ m → Microwaves: about 10⁻² m → Radio waves: 1 m and more
Why the others are wrong
(b) 10⁻¹⁰ m is X-ray range.
(c) 10⁻² m is microwave range.
(d) 10⁰ m (1 m) is radio waves.
The trap
Convert: UV ≈ 10⁻⁷ m.
Also know
Ultraviolet has three bands. UV-C is the most harmful and is fully absorbed. UV-B is mostly absorbed by ozone; the part that gets through causes sunburn, skin cancer and cataract and damages phytoplankton. UV-A mostly reaches the ground.
🔒 UV-C 100–280 nm, UV-B 280–315, UV-A 315–400. Ozone blocks UV-C and most UV-B.