The Visible Spectrum

• When white light passes through a prism,

it is separated into its constituent colors:
the red, orange, yellow, green, blue, indigo
and violet. These colors do not distinctly
separate but they continuously change
from red to violet. Red color has the
longest wavelength from among these
colors and violet has the shortest.
• Our eyes are sensitive to electromagnetic waves of
wavelengths that ranges from 4x10-7 m to 7x10-7 m.
This is the range of wavelengths of white light. Thus, the
spectrum of white light is therefore called the visible
spectrum. Table 3 shows the wavelengths of the
different colors that constitute the white light.

Color Wavelength (nm)

Violet- Indigo 390 to 455
Blue 455 to 492
Green 492 to 577
Yellow 577 to 597
Orange 597 to 622
Red 622 to 700
 LIGHT: MIRRORS &
LENSES
• In the previous module, you learned about
electromagnetic spectrum.
• You gained an understanding of the
different electromagnetic waves and their
benefits. One of the most common among
these electromagnetic waves is the visible
light.
• In this module, you will study two of the
properties of visible light - reflection and
refraction. A closer look into these properties will
be done through different observable examples
and experimentations using mirrors and lenses.
• As you walk through the pages of this module,
you will be able to use the laws of reflection and
refraction in order to describe and explain how
images are formed by mirrors and lenses. You
will also be able to solve problems pertaining to
the position and magnification of images formed
by mirrors and lenses.
• One of the thrusts of this module is to
make you aware of the purposes of the
different types of mirrors and lenses so
you can select the right type of mirrors and
lenses that you can use in your daily lives.
 Learning
Competencies/Objectives
1. Predict the qualitative characteristics
(location, orientation, type, and
magnification) of images formed by plane
and curved mirrors and lenses.
2. Determine the quantitative characteristics
(location, orientation, type, and
magnification) of images formed by plane
and curved mirrors.and lenses.
3. Distinguish between converging and
diverging mirrors and lenses.
4. Apply ray diagramming techniques in
describing the characteristics and positions
of images formed by mirrors and lenses.
5. Derive the mirror and lens equations.
6. Identify ways in which the properties of
mirrors and lenses determine their use in
optical instruments (e.g., cameras and
telescopes).
Facts about Light
 It is a form of Electromagnetic Energy
 It is a part of the Electromagnetic Spectrum and the only part we
can really see
 What is light?

We see light as color and

brightness
It’s actually electromagnetic
radiation:
Partly electric, partly magnetic
Flows in straight line (radiates)
Facts about Light
The speed of light, c, is constant in a vacuum.
Light can be:
•REFLECTED
•ABSORBED
•REFRACTED

Light is an electromagnetic wave in that it has wave like properties

which can be influenced by electric and magnetic fields.
 Speed of light
• Light travels at 300,000,000
meters/second
• It takes 8 minutes for a light wave (or a
photon) to travel from the sun to the earth.
• We see the moon because it reflects the
sun’s light
• It takes 1 second for light reflected off the
moon to reach the earth.
The waves can pass through the object

The waves can be reflected off the object.

The waves can be scattered off the object.

The waves can be absorbed by the object.

The waves can be refracted through the object.

• Incident Ray. The ray of light approaching
the mirror represented by an arrow
approaching an optical element like
mirrors.
• Reflected Ray. The ray of light which
leaves the mirror and is represented by an
arrow pointing away from the mirror.
• Normal Line. An imaginary line (labeled N
in Figure 3) that can be drawn
perpendicular to the surface of the mirror
at the point of incidence where the ray
strikes the mirror.
• The angle between the incident ray and
the normal line is known as the angle of
incidence, Өi. The angle between the
reflected ray and the normal is known as
the angle of reflection, Өr.
 Multiple Images
• Reflection not only happens on a smooth
surface like plane mirrors, but also
happens on rough surfaces. This is why
reflection is classified into two types.
 Types of Reflection
1. Specular/ Regular Reflection. This is a
reflection of light on smooth surfaces such
as mirrors or a calm body of water. An
example of this is the image of the Mayon
volcano on a calm water.
2. Diffused/Irregular Reflection. This is a
reflection of light on rough surfaces such as
clothing, paper, wavy water, and the asphalt
roadway. An example of this is the image of
a mountain on a wavy body of water.
 Reflection on Spherical Mirrors
• A curved mirror is a reflecting surface in
which its surface is a section of sphere.
There are two kinds of curved mirrors, the
concave and the convex mirrors. A spoon
is a kind of a curved mirror with both
concave and convex surfaces.
 Two types of Spherical Mirrors
1. The Concave Mirror
• It is a curved mirror in which the reflective
surface bulges away from the light source.
• It is called Converging Mirror because the
parallel incident rays converge or meet/ intersect
at a focal point after reflection.
2. The Convex Mirror
• It is a curved mirror in which the reflective
surface bulges towards the light source.
• It is called Diverging Mirror because the parallel
incident rays diverge after reflection. When
extending the reflected rays behind the mirror, the
rays converge at the focus
behind the mirror.
 Images Formed by Curved Mirrors
• In locating the image formed in curved mirror
graphically, three important points are
considered.
1. Center of Curvature, C - the center of the
sphere of which the mirror is part. Its
distance from the mirror is known as the radius.
2. Vertex, V - the center of the mirror.
3. Focal Point/ Focus, F – the point between the
center of the curvature and vertex. Its distance
from the mirror is known as the focal length, f.
 Curved Mirrors
(a) Concave Mirror (b) Convex Mirror
 The ‘Four Principal Rays’ in Curved
Mirrors
• Images formed in a curved mirror can be
located and described through ray
diagramming. The P – F ray, F – P ray, C
– C ray, and the V ray are the ‘Four
Principal Rays’ in curve mirrors. These
rays, applied for concave and convex
mirrors.
 Concave Mirror
(Converging Mirror)
1. P – F Ray. A
ray of light parallel
to the principal
axis is reflected
passing through
the principal focus,
F.
• 2. F – P Ray. A ray of
light passing through
the focus, F is reflected
parallel to the principal
axis.
• 3. C – C Ray. A ray of
light passing through
the center of
curvature, C reflects
back along its own
path.
• 4. V Ray. A ray of
light directed to the
vertex reflects at
equal angle from the
principal axis
Convex Mirror (Diverging Mirror)
• 1. P – F Ray. A ray of
light parallel to the
principal axis is
reflected as if passing
through the principal
focus, F.
• 2. F – P Ray. A ray of
light directed towards
the focus, F is
reflected parallel to
the principal axis.
• 3. C – C Ray. A ray of
light directed towards
the center of
curvature, C reflects
back along its own
path.
• 4. V Ray. A ray of
light directed to the
vertex reflects at
equal angle from the
principal axis.
 Location, Orientation, Size, and Type of
Image Formed in Curved Mirrors
LOCATION OF IMAGE
OBJECT LOCATION Orientation Size (same, Type
(upright or reduced or (real or
inverted) enlarged) virtual)
A. CONCAVE Between Inverted Reduced Real
• Farther than the C and F
Center of Curvature
• At the Center of At C Inverted Same Real
Curvature
• Between the Center Beyond Inverted Enlarged Real
of Curvature and the C
Focal point
• At the Focal point No Image Formed
• Between the Focal Behind Upright enlarged virtual
point and the Center the
of the lens (Vertex) Mirror
B. CONVEX Between F Upright reduced Virtual
• All and V
locations
The Sign Conventions for Mirror
• f is positive (+) if the mirror is a concave mirror
• f is negative (-) if the mirror is a convex mirror
• q is (+) if the image is a real image and located
on the object’s side of the mirror.
• q is (-) if the image is a virtual image and located
behind the mirror
• h’ is (+) if the image is an upright image
• h’ is (-) if the image an inverted image
 Images Formed by Lenses
• In locating the image formed in lenses graphically, two
important points are considered. The following important
points are enumerated below.
1. Vertex, V – The geometric center of the lens.
2. Focal point/ Focus, F – A point where light rays converge
(or appears to converge) when parallel light rays pass
through a lens. Its distance from the vertex is called the
focal length.
 The ‘Three Most Useful Rays’ in Lenses

• Images formed in a lens can be located

and described through ray diagramming.
The following three most useful rays for
convex and concave lenses are presented
below.
Convex Lens (Converging Lens)

1. P–F Ray. A ray of

light parallel to the
principal axis is
refracted passing
through the principal
focus, F behind the
lens.
2. F–P Ray. A ray of
light passing through
the focus, F in front of
the lens is refracted
parallel to the principal
axis.
3. V Ray. A ray of light
passing through the
exact center of the lens
(vertex) continue to
travel in the same
direction.
Concave Lens (Diverging Lens)
1. P–F Ray. A ray of
light parallel to the
principal axis is
refracted as if passing
through the principal
focus, F in front of the
lens.
2. F–P Ray. A ray of
light directed towards
the focus, F behind the
lens is refracted parallel
to the principal axis.
3. V Ray. A ray of light
passing through the
exact center of the lens
(Vertex) continue to
travel in the same
direction.