Chapter 12

Question 1

refraction

Answer 1

the bending or change in direction of light when it travels from one medium into another

Question 2

what causes refraction?

Answer 2

a change in the speed of light in a medium

Question 3

how fast is the speed of light in a vacuum, water, and acrylic

Answer 3

c = 3.00 x 10^8

water = 2.26 x 10^8

acrylic = 1.76 x 10^8

Question 4

angle of refraction

Answer 4

the angle between the refracted ray and the normal

Question 5

the rules for refraction

Answer 5

1. the incident ray, refracted ray, and the normal all lie on the same plane, and the incident ray and refracted ray are on opposite sides of the line separating the media
2. light bends toward the normal when the speed in the second medium is less than the first, and it bends away from the normal when the speed in the second medium is greater

Question 6

what is the principle of the reversibility of light

Answer 6

light still follows the same path even if you switch its original direction

Question 7

why do spoons look bent in water / behind where it really is

Answer 7

• the brain thinks that the spoon is behind where it really is because light is refracted away from the normal when travelling from water into air
• the human brain perceives light in a straight line, so it will project these light rays backward to a virtual light source behind the spoon

Question 8

partial reflection and refraction

Answer 8

when light reflects off a surface, but is also refracted
(ie/ on water images are seen from reflection and fish are seen from refraction or mirrored sunglasses)

Question 9

index of refraction

Answer 9

the ratio of the speed of light in a vacuum to the speed of light in a medium, n = c/v, or n = sin(<i)/sin(<R)

it is a dimensionless quantity

it is inversely proportional to the speed of light in that medium

Question 10

what does a higher index of refraction say about the speed of light travelling through it

Answer 10

the greater the index of refraction, the more the speed of light will slow down in that material

(ie/ for air n = 1.00 and diamond n = 2.42)

the relationship is inversely proportional, higher index slower speed

Question 11

critical angle

Answer 11

the angle of incidence that results in an angle of refraction of 90 degrees

Question 12

total internal reflection

Answer 12

• the situation when the angle of incidence is greater than the critical angle
• the refracted ray will no longer exit the medium, but instead reflects back into the meeting and disappears (only a reflected ray is visible)

Question 13

when does total internal reflection occur

Answer 13

total internal reflection occurs when two conditions are met:
1. light is travelling more slowly on the first medium than the second
2. the angle of incidence is large enough that no refraction occurs in the second medium (instead the ray is reflected back into the first medium)

Question 14

why do diamonds sparkle

Answer 14

they are cut a certain way, have a high index of refraction, and have a small critical angle of 24.4 degrees, therefore it often undergoes total internal reflection and sparkles

Question 15

fibre optics

Answer 15

• a technology that uses light to transmit information along a glass cable
• the light must not escape so it needs to have a small critical angle
• used in communications industry for phones, computers, and TVs

Question 16

the triangular prism

Answer 16

• exhibits total internal reflection
• glass has a critical angle of about 41.1
• prisms are more useful in optics than mirrors (mirrors lose light through absorption and deteriorates)
• the emergent ray can either be 90 or 180 degrees
• used in cameras, binoculars, and periscopes

Question 17

retro-reflector

Answer 17

an optical device in which the emergent ray is parallel to the incident ray
- ie/ corner of a glass cube and used in road signs to see them at night

Question 18

apparent depth

Answer 18

• the depth that an object appears to be at due to the refraction of light in a transparent medium
• images in water are higher than the actual object, so items seem closer to the surface than they actually are

Question 19

the flattened sun

Answer 19

• at sunset close to the horizon, light from the bottom of the sun is refracted more than light from the top of the sun
• this is because air is more dense near earths surface (greater refraction)
• the bottom light rays also have a greater angle of incidence resulting in the sun having a flattened appearance

Question 20

the mirage

Answer 20

• a virtual image of the sky reflected on the road like water on pavement
• can appear when travelling from cool air to warmer air
• as air gets warmer closer to the ground, the light ray reflects further away from the normal until TIR happens
• now the light ray travels up from the hottest layer and is gradually refracted toward the normal as the temp decreases until it enters the eye

Question 21

shimmering on a lake by the moon

Answer 21

• caused by light being refracted as it passes through air of different temps
• the air just above a lake is warmer than air further away
• light travels slower in the further colder air so it bends to the normal
• as it continues down to the warmer air, it’s speed increased and bends farther away from the normal
• eventually total internal reflection occurs and results in virtual images of the moon

Question 22

dispersion

Answer 22

the separation of white light into its constituent colours (through a prism)
- violet light refracts more and bends more toward the normal than red light because it’s speed of light is slower

Question 23

the rainbow

Answer 23

steps to making a rainbow:
1. refraction as light from air enters the raindrop, resulting in dispersion
2. partial internal reflection when this light hits the back of the raindrop
3. refraction as the light now exits the raindrop

Question 24

thin lens / mirror equation

Answer 24

1/F = 1/di + 1/do

Question 25

fermat’s principle

Answer 25

aka principle of least time, links ray and wave optics states that the path taken by a ray between two given points is the path that can be travelled in the least time

Question 26

magnification equation

Answer 26

M = -(di)/do OR M = hi/ho

Question 27

what causes a mirage

Answer 27

the bending or reflection of rays of light by a layer of heating air of varying density

Question 28

what are the types of optical illusions

Answer 28

1. physiological: occur when the brain is trying to figure out a pattern 2. cognitive: based on a persons perception of the world 3. literal: intentionally created by combining many smaller images to create a larger image

Question 29

snell’s law

Answer 29

used to describe the relationship between the angles of incidence and refraction n1(sin0i) = n2(sin0R)

Question 30

when is the only time you can see a rainbow

Answer 30

when the sun is behind you; the brain projects the light rays backwards to form a virtual image of the spectrum

Question 31

what happens when light travels from something more dense to something less dense?

Answer 31

it bends away from the normal

Question 32

what happens when light travels from something less dense to something more dense?

Answer 32

it bends toward the normal

Question 33

what is the index of refraction of air, water, acrylic, and diamond

Answer 33

- air/vacuum: 1.00 - water: 1.33 - acrylic: 1.49 - diamond: 2.42