Optics Flashcards
Light
Form of energy that travels in electromagnetic waves (speed = 3 x 10⁸ m/s)
Crest
Highest point of wave
Trough
Lowest point of wave
Resting Position
Level of water with no waves
Wavelength
Distance from one point in the wave to another similar point (measured in nanometers - nm = 1 x 10⁻⁹ m, represented by lambda λ)
Amplitude
Height of wave from resting position - amplitude = intensity
Frequency
cycles/second = hertz (Hz) - frequency = energy
Electromagnetic Spectrum
Radio Waves, Microwaves, Infrared Light, Visible Light, Ultraviolet Light, X-Rays, Gamma Rays
Radio Waves
AM/FM radio, cellular communication, tv signals, radar, astronomy
Microwaves
Telecommunication, microwaves, astronomy
Infrared Light
Heat detection, remote controls, lasers, astronomy
Visible Light
Human vision, theatre/concert lighting, rainbows, lasers, astronomy
Ultraviolet Light
Tans skin, sunburns, simulates vitamin D production, “black” lights, sterilization, astronomy
X-Rays
Medical imaging, cancer treatment, security, astronomy
Gamma Rays
Product of some nuclear decay, cancer treatment, astronomy
Visible Light and Colours
Longest to shortest wavelengths: red, orange, yellow, green, blue, indigo, violet
Natural Sources of Light
Bioluminescence, Sun, stars, aurora borealis, volcanoes (incandescence)
Artificial Sources of Light
Chemiluminescence, fluorescence, phosphorescence
Incandescence
Light produced from high temperatures (ex. volcanoes, light bulbs, red stove burners, white hot iron)
Light bulbs: electric current runs through filament causing it to heat up and produce light (inefficient - only 5% of energy converted to light)
Electric Discharge
Light produced when electric current is passed through a gas (ex. sodium/mercury vapour bulb, lightning)
Light-Emitting Diodes (LEDs)
Semiconductors that emit infrared/visible light when charged with an electric current (ex. billboards, clocks, signs)
Luminescence
Light produced for any reason other than for a rise in temperature
Fluorescence
Light produced from exposure to electromagnetic radiation (ex. light bulbs, some minerals, “black” light, germicidal lamps)
Light bulbs: electrons collide with mercury gas to produce UV light that is absorb by phosphor lining the sides, causing it to glow (more efficient and longer life - 20-30% of energy converted to light, but disposal problems)
Phosphorescence
Light produced from exposure to electromagnetic radiation even after the absence of radiation - light is stored and released slowly over a period of time (ex. glow-in-the-dark objects, glowing paint, some safety signs)
Chemiluminescence
Light produced from a chemical reaction without a rise in temperature (ex. glow sticks, some bioluminescent animals - fireflies)
Bioluminescence
Light produced from living organisms (ex. fish, jellyfish, sea stars, fireflies)
Functions: mimicry, counterillumination, attracting mates, distracting predators, camouflage, warning, communication, illumination)
Triboluminescence
Light produced from friction (ex. quartz, diamonds, Wintergreen Lifesavers)
Law of Reflection for Plane Mirrors
angle of incidence = angle of reflection
Plane Mirrors
Image is always (LOST):
behind the mirror, upright, same size, and virtual
Mirror Applications
Concave/Converging: flashlights, telescopes, cosmetic mirrors, car headlights
Convex/Diverging: security mirrors, side-view mirrors on automobiles
Shadows
Size of shadow depends on object’s size and distance from the light source
Smaller light source: sharp, well defined shadow
Larger light source: fuzzy shadow
Umbra: darkest part of shadow
Penumbra: lighter parts of shadow
Refraction
The bending of light as it travels between mediums
- Light bends because of the difference of the speed of light in different mediums (light is slower in denser materials)
- When speed of light is slower in second medium = refracted towards normal
- When speed of light is faster in second medium = refracted away from normal
Index of Refraction
Ratio of the speed of light in a vacuum to the speed of light in a medium (n = c/v)
Dispersion
Process of separating white light into its spectrum of colours - each colour travels at a different speed (blue is slower than red - blue gets refracted more)
Partial Reflection and Refraction
When travelling from one medium to another, some light is reflected, some is refracted (amount of reflection/refraction depends on angle of incidence and densities of the mediums)
The Critical Angle
- As angle of incidence increases, angle of refraction gets closer to 90 degrees (angle of incidence < critical angle)
- When angle of incidence = critical angle, refracted line lays on the boundary (no light passes through to second medium)
- When angle incidence > critical angle, no light passes through, all light is reflected (total internal reflection)
Applications of the Critical Angle
Binoculars, optical fibres, perfect-cut diamond, retro-reflectors
Cornea
Thin layer of transparent tissue (550 micrometers - µm) with 75% of eyes total refractive power (n = 1.37)
Pupil
Dark circular opening that allows light to enter the eye
Iris
Coloured band of muscles that control the size of the pupil (controls the amount of light let into the eye)
Lens
Convex lens that can adjust its focal length because of ciliary muscles
When muscles contract = lens becomes thicker, refractive power increases, focal length decreases (for nearby objects
When muscles relax: lens becomes thinner/flatter, focal length increases (for distant objects)
Retina
Inner lining of back of eye that the image is projected on made of photoreceptor cells sensitive to light
Rod Cells
Detects shape and movement in low light, but can’t detect colour (only shades of grey) - found in peripheral areas of retina
Cone Cells
Detects colour: three types that are sensitive to each of the primary colours of red, green, or blue - found in central area of retina
Blind Spot
Area in retina that has no photoreceptor cells and can’t detect light because it is where the optic nerve connects the eye to the brain
Hyperopia/Far Sightedness
Eye is too short and image forms behind the retina - can’t see nearby objects clearly (corrected with a converging lens)
Myopia/Near-Sightedness
Eye is too long and image forms in front of the retina - can’t see distant objects clearly (corrected with a diverging lens)
Astigmatism
Irregular cornea causes irregular refraction on an axis from 0 to 180 degrees - forms blurry images (corrected with a toroidal lens that has multiple focal lengths)
Presbyopia
As people get older, their lens hardens and becomes less flexible, while ciliary muscles get weaker, meaning the lens is less able to expand into its near focusing shape - less able to accommodate for near distances (corrected with a converging lens)
