Presentation on theme: " 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)"— Presentation transcript:
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) 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.
Ex. If a light wave has a frequency of 500,000 Hz, what is its wavelength? V = f λ 3.00 x 10 8 = 500,000 λ 600 m Given: F = 500,000 Hz λ = ?
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
Visible Spectrum – Light we can see Y R O Y G B I V Largest to Smallest Wavelength. Larger wavelength = Lower frequency = less energy Shorter wavelength = Higher frequency = more energy
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
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.caused by the change in speed
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 (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: n 1 sin( 1 ) = n 2 sin( 2 ) n 1 = index of refraction of medium 1 θ 1 = incident angle or θ i n 2 = index of refraction of medium 2 θ 2 =refracted angle or θ r To calculate: BE IN DEGREE MODE!
28 o 10° o n 1 = 1.0 air Snell’s Law Example A person is shinning a flashlight (through air 1.0) into an unknown medium (n 2 ). The light enters at 28° to the normal line. It becomes 10 °within the 2 nd medium. Calculate the index of refraction of the 2 nd medium? n 2 = ? 10 o
n 1 = 1.00 1 = 28 ° 2 = 10 °θ n 2 = unknown index (1.00) sin(28) = n 2 (sin 10) = n 2 (0.174) Divide by n 2 = 2.70 We can then check this value against the list of known refractive indexes and identify the material. Snell’s Law - Example
Given: n i = 1.00, n r = 1.33, θi = 45 ° Find θr 1.00 * sine (45 °) = 1.33 * sine (θr) = 1.33 * sine (θr) = sine (θr) sine -1 (0.532) = sine -1 ( sine (θr)) 32.1 ° = θr 45°
Index of refraction(n)=speed of light in a vacuum(c) speed of light in material (v) Another Equation … Practice Problem Calculate the speed of light in water. Water has an index refraction of = 3x10 8 m/s n n =