what is light? light is a kind of electromagnetic radiation. light travels in transverse waves. ...
TRANSCRIPT
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?
V = f λ3.00 x 108 = 500,000 λ 600 m
Given:F = 500,000 Hzλ = ?
Radiowaves
Microwaves
Infrared .
Ultra-violet
X-Rays
GammaRays
Visible Light
ELECTROMAGNETIC SPECTRUM
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 seeR O Y G B I V
Largest to Smallest Wavelength.Larger wavelength = Lower frequency = less energyShorter 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 wavelengthLow frequencyLow energy
Short wavelengthHigh frequencyHigh 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 tomore 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 densemedium 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!
28o
10°o
n1 = 1.0 air
Snell’s Law Example
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?
n2 = ?
PRACTICE
10o
N1SIN(Θ 1) = N2SIN(Θ 2)n1 = 1.00q1 = 28 °q2 = 10 °θn2 = 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.
Snell’s Law - Example
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
Index of refraction(n)=speed of light in a vacuum(c) speed of light in material (v)
Another Equation …
Practice ProblemCalculate the speed of light in water. Water has an index refraction of 1.33.
1.33 = 3x108m/s n n =