Electromagnetic Waves and Reflection

Electromagnetic Waves

• Light has a dual nature, both particle and wave.
• Particle nature: light consists of photons.
• Wave nature: characterized by wavelength and frequency.
• Photons have energy (E = hν), where h is Planck's constant (6.62607×10⁻³⁴ Js) and ν is frequency.
• Visible light is a portion of the electromagnetic spectrum, covering roughly 400-700 nm.
• Light is electromagnetic radiation.

Reflection

• Reflection occurs when light strikes a surface separating two mediums.
• The law of reflection states the angle of incidence equals the angle of reflection.
• Reflection can be specular (smooth surfaces) or diffuse (rough surfaces).
• Reflectance is the ratio of reflected power to incident power.

Lambert's Cosine Law

• The total radiant power observed from a Lambertian surface is directly proportional to the cosine of the angle between the observer's line of sight and the surface normal.
• It's also known as the cosine emission law or Lambert's emission law.

Refraction

• Light changes direction when passing from one medium to another due to changes in velocity.
• This phenomenon is easily observed with objects partially submerged in water.

Absorption

• Electromagnetic waves can be partially absorbed by a medium, producing an effect like heat.
• The amount of absorption depends on wavelength/frequency, angle of incidence, nature of the medium, and intensity of radiation.
• The light reflected by an object determines its color. Color isn't due to absorbed but reflected light.

Law of Grotthus Draper

• This law describes the inverse relationship between penetration and absorption of energy.
• If energy is not absorbed it is transmitted to deeper tissues.
• The more energy absorbed, the less transmitted and the less penetration.

Arndt-Schulz Principle

• Small doses of a substance stimulate, moderate doses inhibit, large doses kill.
• A small stimulus may have no biological effect, but a moderate stimulus may have a biostimulatory effect, while a large stimulus may have a bio-inhibitory effect.

Inverse Square Law

• Intensity of radiation striking a surface is inversely proportional to the square of the distance from the source.
• The closer the source of radiation, the greater the intensity received by the skin.
• The further away from the source, the less the intensity of received radiation.

Medical Applications of Light

• Light is beneficial in medicine for both diagnostic and therapeutic purposes.
• Diagnostic use: visual information gathering of the patient (e.g., using mirrors to see inside body openings).
• Endoscopes: instruments for viewing internal body cavities (e.g., cystoscopes, proctoscopes, bronchoscopes, colonoscopes).
  • Flexible endoscopes are used to reach areas inaccessible with rigid endoscopes.
• Transillumination: transmission of light through tissues. Used for detecting conditions like hydrocephalus and pneumothorax.
  • A tool for diagnosis of conditions in infants.
• Light Therapy (phototherapy): using visible light to treat conditions (e.g., jaundice).
• UV light: important in medicine for sterilization of medical instruments due to germicidal properties.
  • Also produces vitamin D in humans, beneficial but also has harmful effects like sunburn and cataracts on the eye.
• IR light: used in physical therapy; warmth due to heat; damage to retina if not filtering the right light.