Untitled

Electromagnetic Radiation

  • Definition: Describes waves created by the motion of electrically charged particles.

Key Terms

  • Photon: A small packet of light energy.
  • Medium: A substance through which light travels.
  • Wavelength: The distance from one crest (top of wave) or trough (bottom of wave) to the next crest or trough.
  • Visible Light: The only waves that the human eye can detect.

States of Matter Regarding Light Production

  • Ground State: An electron in its normal place.
  • Luminous: Objects that can produce their own light.
  • Non-luminous: Objects that do not emit their own light.

Processes of Light Production

  • Incandescence: Production of light through heating up a material.
  • Electric Discharge: Light produced by passing electricity through a gas, causing it to glow.
  • Fluorescence: An object absorbs UV light and immediately emits it as visible light.
  • Phosphorescence: Light emitted due to exposure to UV light, continues to be emitted even when the UV light is off.
  • Chemiluminescence: Light produced by a chemical reaction with little or no change in temperature.
  • Bioluminescence: Light produced by a chemical reaction in living organisms.
  • Triboluminescence: Light produced when certain crystals are scratched, crushed, or rubbed.

Light Behavior

  • LED (Light Emitting Diode): Light produced from electric current flowing through a semiconductor like silicon.
  • Refraction: The bending of light as it travels from one medium to another.
  • Index of Refraction (n): The ratio of the speed of light in a vacuum to the speed of light in another medium.
  • Transparency Classification:   - Transparent: Allows ALL light to pass through.   - Translucent: Allows SOME light to pass through.   - Opaque: Allows NO light to pass through.

Wavelength and Energy

  • Wave Characteristics:   - The distance between two identical points on a wave is a key characteristic.   - Longest Wavelength: Radio Waves.   - Shortest Wavelength: Gamma Waves.   - Energy Relationship:     - Shorter wavelength = higher energy.     - Longer wavelength = lower energy.

Parts of the Human Eye

  • Sclera: The white part of the eye.
  • Vitreous Humour: Jelly-like substance that fills the eye.
  • Cornea: Tissue forming a transparent curved structure on top of the pupil, focuses light.
  • Retina: The ‘projection screen’ at the back of the eye, contains rods and cones that respond to light and initiate nerve impulses to the brain.
  • Rod Cells: Sensitive to light but cannot distinguish colors.
  • Cone Cells: Responsible for detecting color.
  • Iris: The colored part of the eye; it opens and closes around the pupil to control the amount of light entering.
  • Pupil: The hole in the iris where light enters the eye.
  • Lens: A flexible converging lens that creates a real, smaller, inverted image on the retina.
  • Optic Nerve: Carries the signal from the retina to the brain.

Focusing of Light

  • Focusing Mechanism: The process where the eye’s lens changes shape to bend light so that it lands clearly on the retina. Actual seeing occurs in the brain.

Vision Deficiencies

  • Myopia (Near-Sightedness):   - Condition where eyes cannot focus on distant objects.   - Caused by an eyeball that is too long, causing the image to form in front of the retina.   - Corrected using a diverging lens.
  • Hyperopia (Far-Sightedness):   - Condition where eyes cannot focus on nearby objects.   - Caused by an eyeball that is too short, causing light rays to reach the retina before they converge.   - Corrected using a converging lens.