Lesson 14.1
How Light Travels
1
describe how light travels;
2
infer that light travels in a
straight line;
3
describe how light travels
in different kinds of
materials;
Objectives
At the end
of the
lesson, you
should be
able to:
Objectives
At the end
of the
lesson, you
should be
able to:
4
explain how shadows are
formed; and
5
classify objects as
transparent, translucent,
and opaque.
Learn about It!
Sun as the Main Source of Light
Sun is the main source of light on
Earth.
It is about one hundred fifty
million kilometers from Earth.
Sun’s distance from earth.
Learn about It!
Speed of Light
Light travels fast.
It moves at a speed of three
hundred million meters per
second in a vacuum.
Light travels faster than sound. This is the
reason why you see the lightning first before
hearing the thunder clap during a
thunderstorm.
Learn about It!
Speed of Light
Sun’s light can reach Earth in
just around eight minutes.
Light travels faster than sound. This is the
reason why you see the lightning first before
hearing the thunder clap during a
thunderstorm.
Learn about It!
The Path of Light
Light travels in a straight line.
This behavior of light can be
observed by putting an
obstacle to the light source.
Sun’s light passes through the
hole on top of the cave in a
straight path.
Learn about It!
What is a shadow?
A shadow is a dark area or pattern
that is formed on a surface when
light rays are blocked by an object.
The shadow usually appears on the
side of the object that is blocking
the light.
Shadows are dark areas
formed on surfaces when
objects block the light.
Learn about It!
How Light Travels Through Different Materials
An opaque material does not allow
light to pass through.
Objects made from wood, metal,
cloth, plastics and concrete are
opaque.
Wooden furnitures are
opaque materials.
Learn about It!
How Light Travels Through Different Materials
Translucent materials allow
some light to pass through.
Some examples of translucent
objects are wax paper and
stained glass windows.
Stained glass windows are
translucent materials.
Learn about It!
How Light Travels Through Different Materials
Objects that allow light to pass
through completely are described
as transparent.
Clear materials are usually
transparent.
Clear glass bottles are
transparent materials.
Learn about It!
How Light Travels Through Different Materials
Therefore, the speed of light changes as it
travels, depending on the material where
it passes through.
Learn about It!
How Light Travels Through Different Materials
The pencil appeared to be broken inside
the glass of water as the speed of light
changes as it travels through the different
states of matter.
Key Points
1
Light travels from its source in a straight path.
2
Light interacts with different materials.
● Opaque materials do not allow light to pass through.
● Transparent materials allow all light to pass through.
● Translucent materials allow some light to pass through.
3
Light travels at different speeds as it passes through
solids, liquids, and gases.
Check Your Understanding
Supply the word that will make each statement
true.
1. Light travels in a __________ path.
2. Some light can pass through __________ objects.
3. Light cannot pass through __________ objects.
4. The __________ of light changes as it passes through different
states of matter.
5. Light travels fastest in __________ where there are no
obstacles.
Challenge Yourself
Can shadows be formed in a completely dark place? Why or
why not?
Bibliography
Jones, Mary, Geoff Jones, and Phillip Marchington. Physics. 2nd ed. Coordinated Science. Cambridge: Cambridge
University Press, 2000.
Dobey, Daniel C., Robert J. Beichner, and Sharon Lee Raimondi. Essentials of elementary science. 2nd ed. Essentials of
Classroom Teaching Series. Boston: Allyn and Bacon, 1999.
Hackett, Dr. Jay, Dr. Richard Moyer, Dr. Joanne Vasquez, Mulugheta Teferi, M.A., Dinah Zike, M.Ed, Dr. Dorothy
Terman, and Dr. Gerald Wheeler. 2013. Science A Closer Look 6. Quezon City: McGraw-Hill Education (Asia) and
Phoenix Publishing House.
Heat Transfer. Accessed August 23, 2017. http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatra.html.
"Temperature
System."
How
does
heat
move?
Accessed
August
http://www.qrg.northwestern.edu/projects/vss/docs/thermal/1-how-does-heat-move.html.
Group,
ACEPT
W3.
"The
Path
of
Light."
Pinhole
Reading.
Accessed
https://www.asu.edu/courses/phs208/patternsbb/PiN/rdg/lightpath/lightpath.shtml.
August
The Propagation of Sound. Accessed August 24, 2017. http://pages.jh.edu/~virtlab/ray/acoustic.htm.
23,
23,
2017.
2017.