Electromagnetic Waves and Reflection

Study Notes

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 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.

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.

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.

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.

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.

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.

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.

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.