Ultraviolet Rays

Ultraviolet Rays: Concept and Properties

Ultraviolet (UV) rays are electromagnetic waves with wavelengths shorter than visible light but longer than X-rays. They lie just beyond the violet end of the visible spectrum.

Wavelength Range

The UV spectrum spans from about $4 \times 10^{-7} \,\text{m}$ (400 nm) down to $6 \times 10^{-10} \,\text{m}$ (0.6 nm). This means UV wavelengths are smaller than those of violet light (which is around 400 nm) and extend into the sub-nanometre region.

Sources of UV Radiation

• Natural source: The Sun is the most important natural source of UV light.
• Artificial sources: Special UV lamps and very hot bodies (like welding arcs) produce UV radiation.

Interaction with the Atmosphere

Most of the Sun's UV radiation is absorbed by the ozone layer in the Earth's atmosphere, located at an altitude of about 40–50 km. This absorption is crucial for life on Earth.

Effects on Humans

• Positive effect: Exposure to UV induces the production of melanin, causing tanning of the skin.
• Harmful effects: Large quantities of UV can cause sunburn, skin damage, and increase the risk of skin cancer.

Key Physical Properties

• Absorption by glass: Ordinary glass absorbs UV radiation. Therefore, you cannot get tanned or sunburn through glass windows.
• Focusing ability: Due to their shorter wavelengths, UV rays can be focused into very narrow beams. This allows high-precision applications like LASIK eye surgery.
• Germicidal action: UV lamps are used to kill germs in water purifiers.

Protective Role of the Ozone Layer …