WHAT IS LIGHT?
 What
is Light?
 Light
is a kind of electromagnetic radiation.
 Light travels in transverse waves.
 Speed of Light (c) = 3.00 x 108 m/s (in a vacuum)
 That’s
186,000 miles per second
At this speed light could
travel the equivalent of 8
times around the world in
one second!

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.
PRACTICE PROBLEM
Ex. If a light wave has a frequency of 500,000
Hz, what is its wavelength?
Given:
F = 500,000 Hz
λ=?
V=f λ
3.00 x 108 = 500,000 λ
600 m
ELECTROMAGNETIC SPECTRUM
Radio Micro Infrared
waves waves .
Ultra- XGamm
violet Rays aRays
Visible Light
ELECTROMAGNETIC SPECTRUM

Radio Waves
 Radio
Stations, 2-way radio, remote controls,
radar (navigation), listening devices (bugs)

Microwaves
 Microwaves,
Cellular phones, speed radars,
Television, Ovens

Infrared
 Movie
– Predator, Police,
Firemen, heating & air
ELECTROMAGNETIC SPECTRUM
 Visible
Spectrum – Light we can see
R
O
Y G
B
I
V
 Largest to Smallest Wavelength.


Larger wavelength = Lower frequency = less energy
Shorter wavelength = Higher frequency = more energy
ELECTROMAGNETIC SPECTRUM

UV light (Ultraviolet Light)
 Sun,

Tanning Beds, Black Lights
X - Rays
 Medical

x-rays, airport security,
Gamma Rays
 Sterilizing
Equipment, Cancer treatments,
Long wavelength
Low frequency
Low energy
Short wavelength
High frequency
High energy
REFRACTION
is the bending of the path of a light wave as it
passes across the boundary separating two
media.
 is caused by the change in speed experienced
by a wave when it changes medium.

• When light travels from a less dense to
more dense medium (light slows down),
the ray is refracted toward the normal.
Example: light slows down when it passes from
air into water
• When light travels from a more dense
medium to a less dense medium (light speeds up), the
ray is refracted away from the normal.
Example: light speeds up when passing from glass
into air
INDEX OF REFRACTION

Index of refraction (n)
Basically it says how hard it is
for light to travel through a media.
 The higher the number the harder it is to travel.

SNELL’S LAW

Snell’s Law:
n1sin(q1) = n2sin(q2)
 n1
= index of refraction of medium 1
 θ1= incident angle or θi
 n2 = index of refraction of medium 2
 θ2 =refracted angle or θr

To calculate: BE IN DEGREE MODE!
PRACTICE
A person is shinning a flashlight (through air 1.0) into an unknown
medium (n2). The light enters at 28° to the normal line. It becomes
10 °within the 2nd medium. Calculate the index of refraction of the
2nd medium?
28o
n1 = 1.0 air
10°
n2 = ?
o
10o
Snell’s Law Example
Snell’s Law - Example
N1SIN(Θ 1) = N2SIN(Θ 2)
n1 = 1.00
q1 = 28 °
q2 = 10 °θ
n2 = unknown index





(1.00) sin(28) = n2 (sin 10)
0.469 = n2 (0.174)
Divide by 0.174
n2 = 2.70
We can then check this value against the list of
known refractive indexes and identify the
material.
INDEX OF REFRACTION
SNELL’S LAW EXAMPLE

Given: ni = 1.00, nr = 1.33,
θi = 45 ° Find θr
1.00 * sine (45 °) = 1.33 * sine (θr)
0.7071 = 1.33 * sine (θr)
0.532 = sine (θr)
sine-1 (0.532) = sine-1 ( sine (θr))
32.1 ° = θr
45°
INDEX OF REFRACTION
Another Equation …
Index of refraction(n)=speed of light in a vacuum(c)
speed of light in material (v)
Practice Problem
Calculate the speed of light in water. Water has an
index refraction of 1.33.
1.33 = 3x108m/s
n
n=