Tru Physics

Ultraviolet (UV) Radiation

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Introduction

Ultraviolet (UV) radiation is a type of electromagnetic radiation that lies beyond the violet end of the visible light spectrum and before X-rays. The wavelengths of UV radiation range from 10 nm to 400 nm, and they are typically divided into three types: UVA, UVB, and UVC.

Planck’s Law

UV radiation, like all electromagnetic radiation, can be described by Planck’s law. Planck’s law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T. It can be written as follows:

I(\lambda, T) = \dfrac{2hc^2}{\lambda^5} \dfrac{1}{e^{\frac{hc}{\lambda k_B T}} - 1}

where:

  • I(\lambda, T) is the spectral radiance,
  • h is Planck’s constant,
  • c is the speed of light,
  • \lambda is the wavelength,
  • k_B is Boltzmann’s constant,
  • T is the absolute temperature (in kelvin).

Types of UV Radiation

UVA (320-400 nm)

UVA has the longest wavelength and accounts for approximately 95% of the UV radiation reaching the Earth’s surface. It can penetrate deep into the skin, leading to aging and long-term damage.

UVB (290-320 nm)

UVB radiation is partially absorbed by the Earth’s atmosphere but is more biologically active than UVA. It’s responsible for sunburn and can cause direct DNA damage, leading to skin cancers.

UVC (100-290 nm)

UVC has the shortest wavelength and is the most harmful type of UV radiation. Fortunately, it’s almost completely absorbed by the Earth’s atmosphere and does not reach the surface. Artificial sources of UVC radiation are used in germicidal applications due to its strong disinfectant properties.

Applications

UV radiation has various applications. It’s used in medicine for treating certain skin conditions, in forensic science for detecting substances not visible in regular light, in meteorology for weather forecasting, and in sterilization and disinfection processes. UV lamps are used in tanning booths and to cure inks and resins.

Despite its benefits, prolonged exposure to UV radiation can cause harmful effects, such as sunburn, skin aging, eye damage, and skin cancer. Hence, protective measures, such as sunscreen and UV-blocking sunglasses, are essential when exposed to strong UV radiation, especially during peak sun hours.

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