Optics

Question 1

Light

Answer 1

Form of energy that travels in electromagnetic waves (speed = 3 x 10⁸ m/s)

Question 2

Crest

Answer 2

Highest point of wave

Question 3

Trough

Answer 3

Lowest point of wave

Question 4

Resting Position

Answer 4

Level of water with no waves

Question 5

Wavelength

Answer 5

Distance from one point in the wave to another similar point (measured in nanometers - nm = 1 x 10⁻⁹ m, represented by lambda λ)

Question 6

Amplitude

Answer 6

Height of wave from resting position - amplitude = intensity

Question 7

Frequency

Answer 7

cycles/second = hertz (Hz) - frequency = energy

Question 8

Electromagnetic Spectrum

Answer 8

Radio Waves, Microwaves, Infrared Light, Visible Light, Ultraviolet Light, X-Rays, Gamma Rays

Question 9

Radio Waves

Answer 9

AM/FM radio, cellular communication, tv signals, radar, astronomy

Question 10

Microwaves

Answer 10

Telecommunication, microwaves, astronomy

Question 11

Infrared Light

Answer 11

Heat detection, remote controls, lasers, astronomy

Question 12

Visible Light

Answer 12

Human vision, theatre/concert lighting, rainbows, lasers, astronomy

Question 13

Ultraviolet Light

Answer 13

Tans skin, sunburns, simulates vitamin D production, “black” lights, sterilization, astronomy

Question 14

X-Rays

Answer 14

Medical imaging, cancer treatment, security, astronomy

Question 15

Gamma Rays

Answer 15

Product of some nuclear decay, cancer treatment, astronomy

Question 16

Visible Light and Colours

Answer 16

Longest to shortest wavelengths: red, orange, yellow, green, blue, indigo, violet

Question 17

Natural Sources of Light

Answer 17

Bioluminescence, Sun, stars, aurora borealis, volcanoes (incandescence)

Question 18

Artificial Sources of Light

Answer 18

Chemiluminescence, fluorescence, phosphorescence

Question 19

Incandescence

Answer 19

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)

Question 20

Electric Discharge

Answer 20

Light produced when electric current is passed through a gas (ex. sodium/mercury vapour bulb, lightning)

Question 21

Light-Emitting Diodes (LEDs)

Answer 21

Semiconductors that emit infrared/visible light when charged with an electric current (ex. billboards, clocks, signs)

Question 22

Luminescence

Answer 22

Light produced for any reason other than for a rise in temperature

Question 23

Fluorescence

Answer 23

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)

Question 24

Phosphorescence

Answer 24

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)

Question 25

Chemiluminescence

Answer 25

Light produced from a chemical reaction without a rise in temperature (ex. glow sticks, some bioluminescent animals - fireflies)

Question 26

Bioluminescence

Answer 26

Light produced from living organisms (ex. fish, jellyfish, sea stars, fireflies) Functions: mimicry, counterillumination, attracting mates, distracting predators, camouflage, warning, communication, illumination)

Question 27

Triboluminescence

Answer 27

Light produced from friction (ex. quartz, diamonds, Wintergreen Lifesavers)

Question 28

Law of Reflection for Plane Mirrors

Answer 28

angle of incidence = angle of reflection

Question 29

Plane Mirrors

Answer 29

Image is always (LOST): behind the mirror, upright, same size, and virtual

Question 30

Mirror Applications

Answer 30

Concave/Converging: flashlights, telescopes, cosmetic mirrors, car headlights Convex/Diverging: security mirrors, side-view mirrors on automobiles

Question 31

Shadows

Answer 31

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

Question 32

Refraction

Answer 32

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

Question 33

Index of Refraction

Answer 33

Ratio of the speed of light in a vacuum to the speed of light in a medium (n = c/v)

Question 34

Dispersion

Answer 34

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)

Question 35

Partial Reflection and Refraction

Answer 35

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)

Question 36

The Critical Angle

Answer 36

1. As angle of incidence increases, angle of refraction gets closer to 90 degrees (angle of incidence < critical angle) 2. When angle of incidence = critical angle, refracted line lays on the boundary (no light passes through to second medium) 3. When angle incidence > critical angle, no light passes through, all light is reflected (total internal reflection)

Question 37

Applications of the Critical Angle

Answer 37

Binoculars, optical fibres, perfect-cut diamond, retro-reflectors

Question 38

Cornea

Answer 38

Thin layer of transparent tissue (550 micrometers - µm) with 75% of eyes total refractive power (n = 1.37)

Question 39

Pupil

Answer 39

Dark circular opening that allows light to enter the eye

Question 40

Iris

Answer 40

Coloured band of muscles that control the size of the pupil (controls the amount of light let into the eye)

Question 41

Lens

Answer 41

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)

Question 42

Retina

Answer 42

Inner lining of back of eye that the image is projected on made of photoreceptor cells sensitive to light

Question 43

Rod Cells

Answer 43

Detects shape and movement in low light, but can't detect colour (only shades of grey) - found in peripheral areas of retina

Question 44

Cone Cells

Answer 44

Detects colour: three types that are sensitive to each of the primary colours of red, green, or blue - found in central area of retina

Question 45

Blind Spot

Answer 45

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

Question 46

Hyperopia/Far Sightedness

Answer 46

Eye is too short and image forms behind the retina - can't see nearby objects clearly (corrected with a converging lens)

Question 47

Myopia/Near-Sightedness

Answer 47

Eye is too long and image forms in front of the retina - can't see distant objects clearly (corrected with a diverging lens)

Question 48

Astigmatism

Answer 48

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)

Question 49

Presbyopia

Answer 49

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)