1. What is Light? What is Light?
Light is a kind of electromagnetic radiation.
Light travels in transverse waves.
Speed of Light (c) = 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!

2. Light travels much faster than sound. For example:
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.

3. 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

4. Electromagnetic Spectrum
Radiowaves
Microwaves
Infrared .
Ultra-violet
X-Rays
GammaRays
Visible Light

5. 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

6. 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

7. Electromagnetic Spectrum
UV light (Ultraviolet Light)
Sun, Tanning Beds, Black Lights
X - Rays
Medical x-rays, airport security,
Gamma Rays
Sterilizing Equipment, Cancer treatments,

8. Long wavelength
Low frequency
Low energy
Short wavelength
High frequency
High energy

9. 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.

10. 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

11. 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.

12. n1sin(q1) = n2sin(q2) Snell’s Law Snell’s Law:
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!

13. Practice Snell’s Law Example 28o
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°o
n2 = ?
10o
Snell’s Law Example

14. Snell’s Law - Example n1sin(θ 1) = n2sin(θ 2) n1 = 1.00 q1 = 28 °
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.

15. Index of refraction

16. Snell’s Law Example Given: ni = 1.00, nr = 1.33, θi = 45 ° Find θr
45°
1.00 * sine (45 °) = 1.33 * sine (θr)
= 1.33 * sine (θr)
0.532 = sine (θr)
sine-1 (0.532) = sine-1 ( sine (θr))
32.1 ° = θr

17. 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 =