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.