Presentation on theme: "What is Light? What is Light?"— Presentation transcript:
1What 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 secondAt this speed light could travel the equivalent of 8 times around the world in one second!
2Light 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.
3Practice ProblemEx. If a light wave has a frequency of 500,000 Hz, what is its wavelength?Given:F = 500,000 Hzλ = ?V = f λ3.00 x 108 = 500,000 λ600 m
6Electromagnetic Spectrum Visible Spectrum – Light we can seeR O Y G B I VLargest to Smallest Wavelength.Larger wavelength = Lower frequency = less energyShorter wavelength = Higher frequency = more energy
7Electromagnetic Spectrum UV light (Ultraviolet Light)Sun, Tanning Beds, Black LightsX - RaysMedical x-rays, airport security,Gamma RaysSterilizing Equipment, Cancer treatments,
8Long wavelengthLow frequencyLow energyShort wavelengthHigh frequencyHigh energy
9Refractionis 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.
10When 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 waterWhen 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
11Index of refraction Index of refraction (n) Basically it says how hard it isfor light to travel through a media.The higher the number the harder it is to travel.
12n1sin(q1) = n2sin(q2) Snell’s Law Snell’s Law: n1 = index of refraction of medium 1θ1= incident angle or θin2 = index of refraction of medium 2θ2 =refracted angle or θrTo calculate: BE IN DEGREE MODE!
13Practice 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?28on1 = 1.0 air10°on2 = ?10oSnell’s Law Example
14Snell’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 0.174n2 = 2.70We can then check this value against the list of known refractive indexes and identify the material.
16Snell’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
17Index of refraction Another Equation … Index of refraction(n)=speed of light in a vacuum(c) speed of light in material (v)Practice ProblemCalculate the speed of light in water. Water has an index refraction of 18.104.22.168 = 3x108m/snn =