# What is Light? What is Light?

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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!

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.

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

Electromagnetic Spectrum

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.

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!

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

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.

Index of refraction

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

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 =