Physics · MU Sofia

22. Ultraviolet

Covers ultraviolet radiation, which spans roughly 10 to 400 nanometres, within the wider context of electromagnetic waves, the spectrum and solar radiation. It notes that UV makes up only a small share of sunlight, that UV-C is largely blocked by the ozone layer, and that UV exposure is linked to skin cancer, pigmentation disorders and collagen damage. The note also briefly compares it with infrared radiation and touches on effects on the biosphere.

Inside: 1 section · 6 labelled pictures · 7 flashcards · 3 min

Topic 23 of 42 in the MU Sofia syllabus for Physics (Dental Medicine, Year 1). The free AceMed note covers it in 1 section, about 371 words (3 min of reading), with 7 flashcards.

In this note

  1. Introduction

Introduction

Summary

  • The notes explore various aspects of electromagnetic radiation, covering its fundamental nature, the electromagnetic spectrum, and specific effects of different wavelengths on the biosphere. Emphasis is placed on visible, infrared, and ultraviolet radiation, detailing their properties, interactions with biological systems, and measurement techniques. The sensitivity of the human eye to visible light and the impact of UV and infrared radiation on health and the environment are highlighted, along with applications like infrared thermography for temperature detection.

Electromagnetic Waves

  • Its Nature: Self-propagating waves formed by coupled electric and magnetic fields, traveling at the speed of light without needing a medium.
  • Speed and Refraction: Propagate at light velocity; the index of refraction (n) is calculated as n = c/v, where c is the speed in vacuum and v in a medium.

Electromagnetic Spectrum

  • Range: Encompasses all frequencies of electromagnetic radiation, categorized by wavelength into radio, microwave, infrared, visible, ultraviolet, X-rays, and gamma rays.

Solar Radiation

  • Properties: Composed of a mix of electromagnetic waves, serving as the primary energy source for all living organisms.
  • Earth Impact: The energy received on Earth's surface varies based on the sun's angle and atmospheric path.

Spectral Sensitivity of the Human Eye

  • Range: 380-800 nm, peak sensitivity at 555 nm.
  • Photometric Vision: Daylight (photopic vision) and dark conditions (scotopic vision) influence perception.

Photometric Quantities and Units

  • Luminous Intensity (I): Measured in candela (lumens per steradian), indicating the amount of flux per unit solid angle.
  • Illuminance (E): Luminous flux per area, measured in lux (lumens per square meter).
  • Brightness (L): Luminous intensity per unit projected area, measured in candela per square meter.

Properties of Infrared and Ultraviolet Radiation

  • Infrared Radiation: Ranging from 1 mm to 750 nm, primarily affects heating and is used in infrared thermography to detect and convert temperature.
  • Ultraviolet Radiation: Ranging from 10 nm to 400 nm, constitutes only 5% of solar radiation. UV-C is mostly blocked by the ozone layer, while other types penetrate clouds and glass. UV radiation can lead to skin cancer, pigmentation disorders, and collagen structure damage.

Applications

  • Infrared Thermography: Detects infrared energy emissions, converting them to temperature readings for various applications.
  • Impact on the Biosphere: UV and infrared radiation have significant biological effects, influencing plant growth, animal behavior, and human health.

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