What is Light? Light is a kind of electromagnetic radiation. Light travels in transverse waves. Speed of Light (c) = 3.00 x 10 8 m/s (in a vacuum)

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 =