Application Of Light Flashcards
1
Q
What is the purpose of the chapter?
A
This chapter discusses the application of light waves
2
Q
What does a simple lens camera consist of?
A
A light-proof box with a converging lens in front and a light sensitive film at the back.
3
Q
What is the function of the lens in a simple lens camera?
A
To focus images of the object to be photographed onto the light-sensitive plate or film.
4
Q
What does the adjustment of distance between the lens and the film allow?
A
So that objects in front of the lens can always be sharply focused on the film.
5
Q
What may the convex lens be replaced by in some cameras?
A
A system of lenses.
6
Q
What is the distance between the lens and the film in a simple lens camera?
A
A fixed distance.
7
Q
What is this fixed distance equal to?
A
The focal length of the lens.
8
Q
What do some cameras have to adjust the distance between the lens and the film?
A
Bellows or focusing rings.
9
Q
What do the diaphragm and the shutter control?
A
The amount of light entering the camera.
10
Q
What does the diaphragm regulate?
A
The size of an aperture or opening which controls the amount of light energy sensitising the film.
11
Q
What does the shutter control?
A
The time interval during which light is allowed to fall on the film.
12
Q
What is this time interval called?
A
The exposure time.
13
Q
What is the first step in making a photograph?
A
Rays of light enter a camera and are focused into an image.
14
Q
What does the light expose the film to?
A
Causing chemical changes on the film’s surface.
15
Q
What is the exposed film treated with in a procedure called developing?
A
Certain chemicals.
16
Q
What is used to make a print by transferring the image from the film to a sheet of special paper?
A
Light.
17
Q
How is a photograph taken?
A
The camera lens is pointed at the object and the focusing ring is used to adjust the distance of the lens from the film until a sharp image is seen on the film.
18
Q
What happens when the button is pressed to take a photo?
A
The shutter quickly opens and closes
19
Q
What happens after the photograph is taken?
A
The film is wound on between two spools until it is all used up.
20
Q
What is a projector?
A
An instrument for projecting on a screen an enlarged image of a transparent object e.g. a slide.
21
Q
What are the essential parts of a projector?
A
A light source
22
Q
What is the function of the light source in a projector?
A
To illuminate the object which is usually non-luminous.
23
Q
What is the function of the converging mirror in a projector?
A
Placed behind the light source
24
Q
What is the condenser in a projector?
A
Consisting of two plano-convex lenses
25
What is usually between the two lenses of a condenser?
An infra-red filter to prevent the passage of heat to the slide which might otherwise melt it.
26
What is the slide carrier?
A framework in which the slide is placed upside down
27
What does the projection lens do?
Placed near the slide
28
What is the distance of the lens from the object?
Between f and 2f
29
What does the screen do?
Usually white
30
What is the principle of the slide projector used in?
Cine-projectors
31
What does the human eye have similar to a camera?
A refracting system containing a converging lens which forms an image of an object in front of the eye on a light sensitive layer at the back of the eye.
32
What are the essential parts of the eye?
The cornea
33
What is the cornea?
The thick transparent bulge in the front part of eye.
34
What does the cornea do?
Serves as a protective covering in front of the lens and allows light into the eye. It also partly focuses the light entering the eye.
35
What are the aqueous humor and the vitreous humor?
The transparent liquid between the cornea and the lens
36
What is the main function of the aqueous and vitreous humor?
To keep the eye in its spherical shape.
37
What is the iris?
The part behind the cornea which gives the colour of the eye.
38
What does the iris act as?
A stop or diaphram of variable size.
39
What is the pupil?
A tiny opening at the center of the iris which regulates the quantity of light entering the eye.
40
Why does the pupil look black?
Because the inner layer of the eye
41
What is the crystalline lens?
It focuses the light from the object on to the light sensitive retina.
42
What are the ciliary muscles?
They support the lens and attach it to the wall of eye
43
What is the retina?
The light sensitive area of cells at the back of the eye where the image is formed.
44
What does the retina consist of?
Light sensitive nerve endings which are connected to the optic nerve.
45
What does the optic nerve do?
Conveys the sensation of sight to the brain.
46
What is the yellow spot?
The most sensitive spot of the retina where light entering the eye are usually brought to a focus and the clearest image is formed.
47
What is the blind spot?
The point of exit of the optic nerve from the retina
48
What is the sclerotic layer?
The outer covering of the eye.
49
What does the optical system of the eye consist of?
The cornea
50
What do they do?
Operate to form a real and inverted image of an external object on the retina.
51
What does the retina transmit?
The impression created on it by this image to the brain through the optic nerve.
52
What does the brain do with the impressions from the retina?
Interprets them.
53
What is accommodation in the eye?
An adjusting mechanism for focusing the image of an object on to the retina by adjusting the focal length of the crystalline lens through the action of the ciliary muscles.
54
What is the function of the ciliary muscles in accommodation?
To control the curvature and hence the focal length of the lens.
55
What happens through the accommodation mechanism?
Both near and far objects can be focused at the retina.
56
How is accommodation defined?
The ability of the eye to alter or adjust the focal length of its lens so as to form clear images of objects at different distances on its retina.
57
How is this adjustment brought about?
Through the action of the ciliary muscles.
58
What happens to see objects close to the eye?
The ciliary muscles increase the curvature of the lens
59
What happens to parallel rays from far objects?
They are focused on the retina. Therefore the normal eye is much relaxed and the lens is slim when viewing far objects.
60
Why do we have binocular vision?
Because our eyes are spaced slightly apart
61
What is the result of our eyes being spaced apart?
The images of the object falling on the retina are not exactly the same. The right eye sees more of the right side of the object
62
What happens when the two images are combined by the brain?
The proper perspective is interpreted.
63
What is binocular vision?
The overlapping of the two images formed by both eyes which gives an impression of depth and solidity and makes it possible for us to see things in relief.
64
Is such a proper perspective of an object possible with one eye?
No.
65
When is binocular vision possible?
Only if the fields of view of the two eyes overlap.
66
Why is binocular vision not possible in some birds?
Because of the location of the eyes.
67
What is persistence of vision?
When light from an object falls on the retina
68
What happens if a light flickers at very short intervals of about ten times per second?
It appears to the eye as a continuous source of light owing to the persistence of vision.
69
What phenomenon is made use of in the showing and production of motion pictures?
Persistence of vision.
70
What does persistence of vision do for still pictures?
Makes them appear to have continuity.
71
What is the near point?
The nearest point at which an object can be clearly seen.
72
What is the far point?
The farthest point at which an object can be clearly seen.
73
What is the near point for a normal eye?
About 25 cm from the eye.
74
What is the significance of the near point?
This is the limit to which the ciliary muscles can operate
75
What is the least distance of distinct vision?
The distance from the near point to the eye.
76
What is the far point for the normal eye?
At infinity.
77
What is the state of the ciliary muscles and lens at the far point?
The ciliary muscles are most relaxed and the lens is slim. The accommodation is also the least.
78
What are two common types of defects of vision?
Long sight and short sight.
79
What causes both defects of vision?
When the eye lens is unable to accommodate effectively.
80
What is long sight (hypermetropia)?
A condition where a person can see far objects but cannot see near objects clearly.
81
What is the near point of a long sighted person?
Farther away than 25 cm
82
Why can't a long sighted person see an object at the normal near point clearly?
Because the rays from the object are brought to a focus at a certain distance behind the retina. This is caused by the eyeball being too short or the crystalline lens not being sufficiently convergent.
83
How is long sight corrected?
With the aid of a suitable converging lens placed in front of the eye. The converging lens reduces the divergence of the rays entering the eye from an object just sufficiently to make the rays appear as if they originated from the near point of the defective eye. Hence a clear image of the object is formed on the retina.
84
What is short sight (myopia)?
A condition where a person cannot see distant objects clearly.
85
Why can't a short sighted person see distant objects clearly?
This is because his eyeballs are too long or the crystalline lens is too converging that rays from distant objects are brought to a focus in front of the retina instead of at the retina.
86
What is the far point of a short sighted person?
Less than the normal far point which is at infinity. Light rays from his far point A are brought to focus at the retina. Therefore objects at A can be clearly seen
87
How can short sight be corrected?
By placing a suitable concave or diverging lens in front of the eye. The action of this lens is to diverge light rays entering the eye from a distant object and make them appear to be coming from the person's far point A.
88
What type of lens is used to correct short sight?
A concave or diverging lens.
89
A short sighted man cannot see clearly objects beyond 90 cm from his eye. How can this defect be corrected?
The defect of short sight is corrected by the use of diverging lens. The image of a distant object must be made to appear to be at 90 cm in order to be seen. Hence u=∞ (infinity) v=-90 cm Using 1/f = 1/v + 1/u = 1/-90 + 1/∞ Since 1/∞ = 0
90
List the similarities between the human eye and the camera.
The camera includes light-tight box painted black inside. The human eye is impregnated with black pigments within. The pupil in the eye serves the same purpose as the aperture of the camera. Both the eye and the camera have converging lens to focus rays from an external object. Both have light sensitive material on which the rays are focused
91
List the differences between the human eye and the camera.
The Human eye has the power of accommodation
92
What is a simple microscope (or magnifying glass)?
A convex lens which is used to produce magnified images of small object.
93
What is a simple microscope used for?
Reading small print and for studying biological specimens.
94
Where is the object placed when a converging lens is used as a simple microscope?
Between the principal focus and the optical centre of the lens. With this arrangement
95
How is the lens moved until the image is seen distinctly?
At 25 cm from the normal eye.
96
What does this image subtend?
A larger visual angle than that produced when the object itself is placed 25 cm from the unaided eye
97
What is a compound microscope?
To produce a higher magnification than that obtained from a simple microscope
98
What are the two converging lenses of short focal lengths in a compound microscope?
The lens (0) nearer this object is known as the objective lens and the lens (E) through which the final image is seen is known as the eyepiece. The eyepiece has a comparatively larger focal length than the objective lens.
99
What does the objective lens produce?
At a magnified
100
Where is the eyepiece adjusted until?
I₁ falls at a distance nearer to it than its principal focus
101
Where does the observer adjust the eyepiece so that the final image is?
At the near point (about 25 cm for a normal eye).
102
What is the magnifying power M of the compound microscope?
The product of the magnifications due to the two lenses. M = M₁ x M₂ where M₁ is the magnification produced by the objective lens and M₂ is the magnification produced by the eyepiece.
103
What is a telescope used for?
Viewing distant objects
104
What is the simplest telescope?
The astronomical telescope.
105
What does the astronomical telescope use?
Two converging lenses
106
What does the objective lens do in an astronomical telescope?
Collects parallel rays from a distant object and forms a real inverted and diminished image I₁ at the principal focus (F₀) of the lens.
107
How is the eyepiece adjusted in an astronomical telescope?
So that the image I₁ of the object falls at a point nearer the eyepiece lens than its focus Fₑ. The eyepiece then acts as a magnifying glass and forms a magnified and virtual image of I₁ at I₂. The lenses can be arranged so that the final image is at infinity.
108
When is the astronomical telescope said to be in normal adjustment?
In such an arrangement the principal focus of the objective must coincide with that of the eyepiece. Thus in normal adjustment
109
What type of image does the astronomical telescope produce?
An inverted image.
110
Is an inverted image a disadvantage?
This can be tolerated when looking at stars
111
To what does the telescope owe its magnifying power?
To the fact that the angle subtended at the eye by the final image at infinity is very much greater than that subtended by the distant object.
112
What type of lenses does the Galilean Telescope use?
A convex lens of long focal length as the objective and a concave lens of short focal length as the eyepiece.
113
How are the two lenses mounted in a Galilean Telescope?
So that they have a common axis with the distance between them equal to the difference between their focal length. This is the Galilean telescope in normal adjustment.
114
What does the objective do in a Galilean Telescope?
Collects parallel rays from a distant object to form a real inverted image at its principal focus.
115
What happens before these rays actually converge to this principal focus?
They are intercepted by the diverging lens which causes the rays to diverge and emerge as a parallel beam. A virtual
116
What is the magnifying power of the telescope given by?
M = focal length of objective / focal length of eyepiece = f₀ / fₑ For high magnification therefore we need an objective of long focal length and an eyepiece of short focal length
117
Can the Galilean telescope be adjusted?
Yes so that the final image forms at the near point. At this instance the telescope is not in normal adjustment.
118
What are Prism Binoculars?
They are essentially a pair of astronomical telescopes each of which is fitted with two right angled isosceles prisms.
119
What happens to the light passing through the objective in Prism Binoculars?
It is reflected from one prism P to another Q and then emerges through the eyepiece.
120
What is the function of the prisms in Prism Binoculars?
To re-invert the image formed by the objective and present an erect image of the object to the eyepiece which subsequently magnifies it. An erect and magnified image is thus presented to the viewer.
121
What are the advantages of Prism Binoculars?
As well as presenting an upright image they are also very compact since they reduce the optical path of the light ray from the objective to the eyepiece
122
What is the formula for the magnifying power of the telescope?
M = focal length of objective / focal length of eyepiece = f₀ / fₑ
123
What is needed for high magnification in a telescope?
An objective of long focal length and an eyepiece of short focal length.
124
What are Prism Binoculars essentially?
A pair of astronomical telescopes each of which is fitted with two right angled isosceles prisms.
125
What is the function of the prisms in Prism Binoculars?
To re-invert the image formed by the objective and present an erect image of the object to the eyepiece which subsequently magnifies it.
126
What are the advantages of Prism Binoculars?
Present an upright image
