In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. ... Like all types of EM radiation, visible light propagates as waves. However, the energy imparted by the waves is absorbed at single locations the way particles are absorbed.

1. The Physics behind
Light by
Somu Rajesh

2. Light
In this Powerpoint presentation:
1) Properties of light
2) Colors
3) Reflection - Mirrors
4) Refraction - Lenses

3. What Is Light?
Light, or Visible Light, commonly refers to
electromagnetic radiation that can be
detected by the human eye. ... Light can
also be described in terms of a stream of
photons, massless packets of energy, each
travelling with wavelike properties at the
speed of light.

4. Properties of Light
Light travels in straight lines:
Laser

5. Light travels much faster than sound. For example:
1) Thunder and lightning
start at the same time,
but we will see the
lightning first.
2) When a starting pistol
is fired we see the
smoke first and then
hear the bang.

6. Light travels VERY FAST – about
300,000 kilometers per second or
186,000 miles per second.
At this speed light
could travel the
equivalent of 8 times
around the world in
one second!

7. Light can create shadows
Shadows are places where light is “blocked”:
Rays of light

8. Light travels in waves
A wave is a disturbance that transfers
energy from place to place.

9. What characteristics do light
waves have?
Light waves are like other kinds of waves.
They have crests, troughs, wavelength,
frequency and speed. However, light waves
are electromagnetic! Light waves have a
component that is electric and magnetic!!

10. We see things because they
reflect light into our eyes! This
is literally the only way we get to
see things! ALL objects we see
either create light or reflect
light!!
Homework

11. Electromagnetic Radiation
•Light is a form of energy called
Electromagnetic Radiation -
Electromagnetic Radiation comes from the sun and
other sources
•Travels at the speed of light
•Is mostly invisible
•Carries energy
•Is VERY important to society and is something YOU
can’t be without for many reasons

12. Properties of Light summary
1) Light travels in straight lines and is a form of
energy
2) Light travels much faster (a million times faster!)
than sound
3) We see things because they reflect light into our
eyes
4) Shadows are formed when light is blocked by an
object
5) Visible light is only a small part of the
electromagnetic spectrum; the other parts are
invisible to the human eye but not necessarily the
eyes of other animals.

13. Part 2 - Reflection and
Mirrors

14. Regular vs. Diffuse Reflection
Smooth, shiny surfaces
have a regular
reflection:
Rough, dull surfaces have
a diffuse reflection.
Diffuse reflection is when
light is scattered in
different directions

15. Using mirrors
Two examples:
1) A periscope
2) A car headlight

16. Types of Mirrors: Plane, Concave, Convex
Plane mirrors are
flat and make
“virtual images”.
The images is
“virtual” because
the light rays do
not come from the
image, they only
appear to

17.  Concave Mirrors are curved inward - just
remember, you go “in” to a cave, and “in” to
a concave mirror!
 Convex mirrors are mirrors that curve
outward
 Convex mirrors are used for security
purposes, in cars etc. They allow us to see
a wide view. The images they make are
virtual

18. Review of Reflection
1. Two types of reflection, regular and diffuse
2. Mirrors come in 3 types: plane, convex and
concave. Each has a distinct shape and use.
3. Mirrors can make virtual images or real
images depending on their type
4. Virtual images - light rays do not meet and
the image is always upright or right-side-up
5. Real images - always upside down and are
formed when light rays actually meet

19. Refraction
•Refraction is when waves speed up or slow down due to
travelling in a different medium
•A medium is something that light waves will travel
through
•Light rays are slowed down by the water
•Causes the ruler to look bent at the surface
• The mediums in this example are water and air

20. The degree that light bends when it enters a
new medium is called the “index of refraction”

21. Light hitting at an
angle is bent
Light hitting
straight on is
not bent

22. Lenses work because of refraction! Light is
bent as it enters a new medium, glass!
1. Thicker in middle, thin
on edges
2. Light rays meet to
form a focal point
3. Makes real images
since light rays come
together from a light
source, but can also
make virtual images
(center picture)
4. Used in cameras,
telescopes, human eye

23. Concave Lenses
1. Concave lenses are
thin in the middle
and thicker on the
edges
2. Since light rays
never meet with
this lens, they make
virtual images only
3. Used in cameras &
telescopes to
correct spherical
aberation, and also
eyeglasses

24. Review of Refraction
1. Light rays slow down when they enter a new
medium
2. Refraction can cause light rays to change
their direction
3. All transparent materials have their own
“index of refraction”
4. Light is refracted when it passes through
lenses and this creates images

25. Color
Part 3 - Color In this section of the
Powerpoint you will learn about color and
how we can mix colors to create other
colors. We will also learn how light helps us
to see various colors around us.

26. Color
White light is not a single color; it is made up of a
mixture of the seven colors of the rainbow.
We can demonstrate this by
splitting white light with a
prism:
This is how rainbows are
formed: sunlight is “split up”
by raindrops.

27. The colors of the rainbow:
Red
Orange
Yellow
Green
Blue
Indigo
VioletJust remember ROY G. BIV

28. Adding colors of light
White light can be split up to make separate colors.
These colors can be added together again.
The primary colors of light are red, blue and green:
Adding blue and red
makes magenta
(purple)
Adding blue and
green makes cyan
(light blue)
Adding all
three makes
white again
Adding red
and green
makes yellow

29. Seeing color
The color an object appears depends on the colors of
light it reflects.
For example, a red book only reflects red light:
White
light
Only red light
is reflected

30. In different colors of light this shirt would look different:
Red
light
Shirt looks red
Shorts look black
Blue
light
Shirt looks black
Shorts look blue

31. A white hat would reflect all seven colors:
A pair of purple trousers would reflect purple light
(and red and blue, as purple is made up of red and blue):
Purple light
White
light

32. Using filters
Filters can be used to “block” out different colours of light:
Red
Filter
Magenta
Filter

33. Some further examples:
Object Color of light
Color object
seems to be
Red socks
Red Red
Blue Black
Green Black
Blue teddy
Red Black
Blue
Green
Green camel
Red
Blue
Green
Magenta book
Red
Blue
Green

34. Investigating filters
Color of filter Colors that could be “seen”
Red
Green
Blue
Cyan
Magenta
Yellow

35. Red
Magenta
White
Yellow
Blue Green
Cyan

36. Part 2 - Reflection and
Mirrors
Reflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of
incidence
Angle of
reflection
Mirror

37. The Law of Reflection
Angle of incidence = Angle of reflection
In other words, light gets reflected from a surface at
____ _____ angle it hits it.
The
same !!!