Ch13 Light Flashcards
1
Q
Define reflection:
A
The change of direction of a ray when it strikes a surface without passing through it
2
Q
Define ray box:
A
Apparatus used to produce a ray of light
3
Q
Define ray:
A
A narrow beam of light
4
Q
Define laser:
A
A device used for producing a narrow beam of light of a single colour (monochromatic)/wavelength
5
Q
Define incident ray:
A
A ray of light arriving at a surface
6
Q
Define reflected ray:
A
A ray of light which has been reflected from a surface
7
Q
Define ray diagram:
A
A diagram showing the path of rays of light
8
Q
Define angle of incidence:
A
The angle between the incident ray and the normal drawn at the point where the ray hits the surface
9
Q
Define normal:
A
The line drawn at right angles to a surface at the point where a ray hits the surface
10
Q
Define image:
A
What we see when we view an object by means of reflected rays
11
Q
Define plane mirror:
A
(Flat mirror)
A mirror with a flat, reflective surface
12
Q
Define laterally inverted:
A
An image in which left and right have been reversed
13
Q
Define real image:
A
An image that can be formed on a screen
14
Q
Define virtual image:
A
An image that cannot be formed on a screen
15
Q
What are the characteristics of the image of an object reflected in a pane mirror?
A
1) Image is the same size as object
2) The same distance behind the mirror as the object is in front of it
3) laterally inverted
4) virtual
5) upright
16
Q
What is a luminous object?
A
Objects that emit their own light
17
Q
True/false: light rays travel in non-linear paths.
A
False
Light rays travel in straight paths
18
Q
True/false: The incident ray, the reflected ray and the normal to the surface lie in different planes.
A
The incident ray, the reflected ray and the normal to the surface lie in the same plane.
19
Q
What are the 2 types of reflection?
A
1) Specular
2) Diffuse
20
Q
What is specular reflection?
A
Reflection of parallel rays of light off a smooth surface so that reflected rays remain parallel
21
Q
What is diffuse reflection?
A
When incident rays are reflected of a rough surface at many different angles.
22
Q
Is the law of reaction applicable to diffuse reflections?
A
No, because the reflected rays shine in arbitrary directions
23
Q
Define refraction:
A
The bending of light when it passes from one medium to another
24
Q
Define angle of refraction:
A
The angle between a refracted ray
and the normal to the surface
at the point where it passes from one medium to another
25
Define speed of light:
Speed at which light travels
(Usually in a vacuum: **3.0 x 10^8 m/s**)
26
Give a word for the definition:
The ratio of the speeds of a light wave in 2 different media.
Refractive Index
27
What’s the equation for refractive index?
n = sin i / sin r
28
Define internal reflection:
When a ray of light strikes the inner surface of a material and some of it reflects back inside it
29
Give a word for:
The minimum angle of **incidence** at which total internal reflection occurs.
Critical angle
30
Define total internal reflection (TIR):
When a ray of light strikes the inner surface of a material and **100%** of the light reflects back inside
31
What is the equation for critical angle?
n = 1 / sin c
32
Where does refraction happen?
At the boundary of 2 materials
33
Why aren’t images through windows distorted because of refraction?
Windows are made of a parallel-sided sheet of glass
So even though the light rays are slightly shifted as they pass through the glass, the image is not distorted because the light rays leave the glass in the same direction as the original direction.
34
When is a light ray not refracted?
When it hits a boundary at 90 degrees
35
What causes the refraction of light?
Because light travels at different speeds
In different materials
36
Does light travel faster in a vacuum or in air?
Vacuum
37
What happens when light passes from air into glass?
The light **slows down** and **bends towards the normal**
38
What happens to light rays when they pass from glass to air?
The light ray bends away from the normal
39
Explain what refractive index of a material is:
It’s a measure of how much light **slows** down/how much it is **bent**.
40
What is the refractive index if the speed of light is halved when it enters a material?
2
41
True or false:
When light rays reach the boundary of another transparent medium, ALL of the rays pass through and are refracted.
False
**Part** of the light rays are **reflected** at the boundary, the **rest** are transmitted through and **refracted**
42
True/false:
The incident and refracted rays lie in the same plane, which also includes the normal to the boundary.
True
43
True/false:
Refraction distorts the image
True, if light from an object changes media on its way to our eye, we see a distorted image.
Remember, same does not happen for a window because they light ray goes back into the same medium as before the window- air
44
What does it mean if a medium has a high index of refraction? (2)
1) medium is more optically dense
2) light travels slower in the medium
45
The **greater** the index of refraction of a medium, the — less the speed of light in that medium
**less**
46
The **greater** the refractive index of the material, the ____ the critical angle
**smaller**
47
How does light travel along a fibre?
By total internal reflection
48
Why must the glass used to carry signals over long distances be of high purity?
So that the glass does not absorb the light
49
What is an endoscope?
A device used to see inside of a patients body
50
Name 3 uses of total internal reflection:
Endoscopy, communications, therapeutic play
51
What 2 requirements are there for total internal reflection to occur?
1) Light has to strike a boundary beyond which the medium has a lower index of refraction
2) The angle of incidence has to be greater than the critical angle
52
Define **converging lens**:
A lens that causes rays of light parallel to the axis to **converge** at the principal focus.
53
Define **diverging lens**:
A lens that causes rays of light parallel to the axis to **diverge** from the principal focus
54
Define **principal axis**:
The line
passing through the centre of a lens
perpendicular to its surface.
55
Define **principal focus/focal point**:
The point at which rays of light parallel to the principal axis converge after passing through a converging lens.
56
Define focal **length**:
The distance from the centre of the lens to its principal focus.
57
Define enlarged:
Used to describe an image that is bigger than the object
58
Define diminished:
Used to describe an image which is smaller than the object
59
Define inverted:
Used to describe an image which is upside down compared to the object
60
Define upright:
Used to describe an image which is the same way up as the object
61
Define spectrum:
(Plural: spectra)
Waves/colours of light, separated out in order according to their wavelengths
62
Define dispersion:
The separation of different wavelengths of light because they are refracted through different angles
63
Define monochromatic:
Describes a ray of light (or other electromagnetic radiation)of a single wavelength
64
What is a characteristic of converging lenses?
They are thicker in the middle
65
What is a characteristic of diverging lenses?
Diverging lenses are thinnest in the middle
66
Are the focal points on either side of the lens equal distances from the lens?
Yes
67
What is another name for a converging lens?
Convex lens
68
When we want to draw a ray diagram of light going through a lens, which 3 rays of light are there?
1) Parallel ray
2) Focal ray
3) Centre ray
69
Give a word for the following:
A ray parallel to the optical axis.
It passes through the focal point on the other side of the converging lens.
Parallel ray
70
Give a word for:
A ray that passes through the focal point of a converging lens emerges parallel to the optical axis on the other side of the lens.
Focal ray
71
Give a word for:
A ray that passes through the centre of the lens continues straight and emerges on the other side with no change in direction.
Centre ray
72
If you draw any 2 of the 3 rays from the top of the object you can find:
Position, Orientation, Size of the image
73
What is another name for a diverging lens?
Concave lens
74
Define focal ray for diverging lenses:
A ray that is heading toward the focal point of the other side of the diverging lens emerges parallel to the optical axis on the other side of the lens.
75
Define parallel ray for diverging lenses:
A ray parallel to the optical axis. It passes to the other side of the diverging lens in a direction as if it was coming from the focal point in front of the lens.
(In front means the side of the lens that the incident rays fall.)
76
Define centre ray for diverging lenses:
A ray that passes through the centre of the lens continues straight and emerges on the other side with no change in direction.
77
What type of lens is a magnifying glass?
A converging lens
78
Compare a thin and fat lens:
Fat lens
More powerful, bends light more
Shorter focal length
Thin lens
Less powerful, doesn’t bend light as much
Longer focal length
79
What lenses are in our eyes?
Converging lenses
80
What do the muscles attached to the converging lenses do?
They enable us to look at objects at varying distances
81
What lens shape is needed to view an object further away?
The lens doesn’t need to be strong
Lens must be longer and thinner for the image to form
82
How does the shape of a lens in the eye look when viewing a closer image?
Lens needs to be stronger
Lens must be shorter and thicker for image to form
83
Why doesn’t the lens of the eye need to be super strong when viewing an image further away?
It is because the light from the image arrives t the lens parralell → lens doesn’t need to bend light much in order to form an image
84
Why must the lens be stronger when viewing an image close up?
Light from the object s diverging and needs to be bent in order to form an image
85
What is another word for short sight?
Myopia
86
What can a person with ** Myopia** see?
→ can see things up close clearly
→ objects further away look blurry
87
What can cause **Myopia**?
Happens when the eyeball is too long → so the rays meet in front of the retina
88
How can **Myopia** be corrected?
By using a diverging lens
It causes the rays from the distant object to diverge → helps lens form a clear image
89
What is another word for **longsight**?
Hyperopia
90
What can a person with **Hyperopia** see?
→ things that are far away
→ they can’t see near objects clearly
91
What causes **Hyperopia**?
→ Short eyeball
→ rays meet behind retina
92
How can **Hyperopia** be corrected?
A converging lens is used → causes rays from close object to converge → helps lens form a clear image
93
What is a prism?
A medium that disperses white light into its component colours
94
What are the colours (in order) that white light is dispersed into?
Red
Orange
Yellow
Green
Blue
**Indigo**
**Violet**
95
How many times does light refract when it passes through the prism?
2
96
What is the evidence that there is no **constant** *Index of Refraction* for white light?
When white light goes through a medium it disperses. The index of refraction of the medium is not constant but it depends on the wavelength
The different colours of light inside of the prism all have a slightly different index of refraction depending on their wavelength. This is known as dispersion
97
What visible colour light has the highest refractive index and is therefore refracted the most?
Violet
98
What visible light colour has the lowest refractive index and is therefore refracted the least?
Red
99
Name a demonstration of dispersion in nature:
Rainbow
100
What produces rainbows?
Combination of refraction and TIR inside spherical rain droplets, combined also with the dispersion of the various colours
