High School
by SSL Technologies
Part 2 /2
Physics Ex-46
PART-2 /2
In studying optics, it is convenient to classify objects into those that
emit light (luminous) and those that reflect light (non-luminous):
LUMINOUS (originate light)
NON-LUMINOUS or ILLUMINATED (do not originate light)
Incandescent Opaque (light cannot pass through)
Neon
Transparent (light and images pass through)
Fluorescent
Translucent (light passes through, images do not)
BEAM OF LIGHT: A beam of light is a "bunch" of light rays.
CONVERGENCE: When rays of light come together to meet at
a point, they are said to converge.
DIVERGENCE: When rays of light go away from a point, they are
said to diverge.
MEDIUM: A medium is the material through which light travels.
Optical mediums are classified according to density.
The more "optically dense" a material is, the slower
light travels in that medium.
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Physics Ex-46
THE PRIMARY COLORS
Monochromatic light is light of one color.
Polychromatic light is light of many colors.
In everyday language we use names to represent monochromatic
light such as red, orange, yellow, green, blue and violet.
Furthermore, each of these colors has a variety of different shades.
Collectively, all the different colors form the “light band” which is
part of the “electromagnetic spectrum”.
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Physics Ex-46
Red, green and blue light (RGB) are called the primary colors.
Adding these three primary colors together forms “white” light.
Adding pairs of the primary colors form the secondary colors.
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Physics Ex-46
The color of an object is determined by the color (or colors)
it reflects.
Suppose white light shines on a red object. The object will
absorb all the colors except red. Thus, it is red.
Study the illustration below.
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Additive color theory
Subtractive color theory
Primary colors: RGB
Primary colors: CMY
Red – Green – Blue
Cyan – Magenta – Yellow
Cyan = Green + Blue
Magenta = Red + Blue
Yellow = Red + Green
Red = Magenta + Yellow
Green = Cyan + Yellow
Blue = Cyan + Magenta
White = Red + Green + Blue
Black = Cyan + Magenta + Yellow
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Physics Ex-46
SHADOWS
Shadows are formed when light is obstructed. The light may be
totally obstructed thereby forming a dark shadow known as an
umbra, or it may be partially obstructed thereby forming a gray
shadow known as a penumbra.
Penumbra (grey)
Umbra (black)
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Physics Ex-46
For example, in diagram-A below, a point source of light encounters an
obstacle (a disc) causing an umbra (total darkness).
In diagram-B, a large source of light causes both an umbra and a penumbra.
Note that when the source is a point, the shadow consists of an umbra
(total darkness) with a well defined outline.
From the side view,
we have two rays
(one to the top of the
obstruction, one to
the bottom of the
obstruction) to define
the shadow (the light
source has no top and
bottom portions).
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Question-1
Physics Ex-46
Define the following terms:
a) Beam of light
A stream of photons emanating (coming from) a light source.
b) Medium
The material through which light travels.
c) Opaque
A material that blocks light (light cannot pass through).
d) Transparent
A material through which light and images pass through.
e) Translucent
A material through which light can pass through but
images cannot pass through.
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Question-2
Physics Ex-46
Define the meaning of the terms monochromatic and
polychromatic light.
Monochromatic is light consisting of only a single color.
Polychromatic is light consisting of many colors.
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Question-3
Physics Ex-46
Draw 5 rays of light that are parallel, converging and diverging.
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Question-4
Physics Ex-46
What does RGB stand for?
Red, Green and Blue.
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Physics Ex-46
Question-5
Fill in the primary and secondary colors in the chart below:
Red
Primary colors
Red
Secondary colors
Green
Yellow
Green
Red
Blue
Blue
Green
Blue
Cyan
Magenta
(light blue)
(light violet)
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Question-6
Physics Ex-46
Define an umbra and explain how it is formed.
The umbra consists of total darkness and is caused by the
total obstruction of the light rays.
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Question-7
Physics Ex-46
Define an penumbra and explain how it is formed.
The penumbra consists of partial darkness and is caused
by the partial obstruction of light rays.
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Question-8
Physics Ex-46
In your own words, define light intensity.
Light intensity (also known as brilliance) refers to the total
number of photons emitted by a light source per second.
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Question-9
Physics Ex-46
Sketch the electromagnetic spectrum and indicate the position
of light.
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Question-10
Physics Ex-46
In the given diagram, measure the length of the umbra and
penumbra of the shadow formed by the obstruction (line).
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Question-11
Physics Ex-46
A beam of white light strikes a glass prism producing an array
of different colors as illustrated below.
What optical phenomena does this represent?
A) Specular reflection
B) Total internal reflection
C) Diffusion
D) Dispersion
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Physics Ex-46
Question-12
The diagram below illustrates light coming from the sun to the
earth with the moon in between.
Which of the following statements correctly describes the shadow
of the moon on the earth?
I-
Region Y is the penumbra
II-
Regions X and Z are the umbra
III- Regions Y is the umbra
IV- Regions X and Z are the penumbra
A) I and II
B) I and IV
C) II and III
D) III and IV
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Physics Ex-46
Question-13
The diagram below illustrates a white light source, a blue filter
and a yellow object.
All the colors
Blue
Blue filter
What color will the object appear?
A) White
B) Black
C) Yellow
D) Blue
A yellow object illuminated by white light will
absorb all the colors except yellow. A blue
filter will filter all the colors except blue.
Thus, when the blue light strikes the yellow
object, it will be absorbed and the object
will appear black (since it reflects no light).
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Physics Ex-46
Question-14
A green filter is placed between a red light source and an object.
Red light source
White object
Green filter
What color is the object?
A) Red
B) Green
C) Yellow
D) White
A green filter will block (absorb) all colors
except green. Since the light source gives
off red light, the green filter will absorb the
red light causing no light to fall on the object.
E) Black
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Physics Ex-46
Question-15
Three different colored objects X, Y and Z, are illuminated by
three projectors. Each projector emits a different colored light.
The first projector causes object X to appear blue while the
other objects appear black.
The second projector causes objects X and Y to appear red
while object Z appears black.
The third projector causes objects X and Z to appear green
while object Y appears black.
What color do the objects appear if while light is used to
illuminate the objects?
White Red Green
Object-X
Object-Y
Object-Z
X Y Z
A) Blue
Black
Black
B) Blue
Red
Green
C) White
Red
Green
2
D) White
Black
Red
3
E) White
Black
Green
1
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