VIEWS: 14 PAGES: 38 POSTED ON: 2/13/2012
Visible Light Region Wavelength Frequency (centimeters) (Hz) Radio > 10 < 3 x 109 Microwave 10 - 0.01 3 x 109 - 3 x 1012 Infrared 0.01 - 7 x 10-5 3 x 1012 - 4.3 x 1014 Visible 7 x 10-5 - 4 x 10-5 4.3 x 1014 - 7.5 x 1014 Ultraviolet 4 x 10-5 - 10-7 7.5 x 1014 - 3 x 1017 X-Rays 10-7 - 10-9 3 x 1017 - 3 x 1019 Gamma Rays < 10-9 > 3 x 1019 • Visible light is the name we give the frequencies of electromagnetic waves our eyes can detect. • Our retinas are made of cells called rods and cones – Cones allow us to see color, but they require more intensity (more waves) in order to send a message to the brain. For that reason, we can’t really see color when there isn't a lot of light. – Rods allow us to detect movement and they don’t require as much intensity (waves) before they send a signal to the brain • Everything that we see is due to the reflection of light. • When you look at something your eyes are interpreting the light that is reflected off of it. Light from sun Yellow light reflected • Opaque: – A word used to describe objects that don’t let light move through them (so you can’t see through them). This is either because they absorb or reflect light. • Transparent: – A word used to describe objects that allow light to travel through them (so it’s almost like they aren't there at all). • Fortunately for us the atmosphere is opaque to high frequency ultraviolet waves, but is transparent to visible light and some UV. • When you see your shadow it is because you are blocking the light from getting through. Color • There are three different types of cones in our eyes. Because of this we are able to see the full range of the visible light spectrum. • The color that you see when you look at something is actually the wavelengths of light that are being reflected. • The colors you don’t see are being absorbed and converted into heat energy. • ROYGBIV • Red is the lowest frequency light • Violet is the highest frequency • All of the colors we see are combination of wavelengths of visible light. • When every wavelength of visible light hits your eyes, they perceive it as white – Because of this we call it “white light” – This is what you see when you look at light from the sun and most light sources, such as lamps. • Something that reflects every wavelength looks white to you. • What do you think something that absorbs all frequencies of light looks like? What frequencies of light are being reflected from / absorbed by this dog? = green is being reflected, every other color is being absorbed = every other color is being reflected/ green is being absorbed What frequencies of light are being reflected from / absorbed by the orange? = every other color is being reflected/ orange is being absorbed = orange is being reflected, every other color is being absorbed What frequencies of light are being reflected / absorbed from the black parts of the 8-ball? = black light is being reflected. = every color is being reflected = every color is being absorbed What frequencies of light are being reflected / absorbed from the seal? = every color is being absorbed. = every color is being reflected • Something that absorbs every frequency of light looks black to you. • An object that is transparent but colored, like stained glass, looks that way because it only allows light of certain frequencies through, the rest it absorbs. • For example red stained glass only lets red through and absorbs everything else. What would you see if you shined pure green light on a red rose? = the rose would look red = the rose would look green = the rose would look black = the rose would look white Pigments • Pigments are particles that absorb and reflect specific frequencies of light. • We can use these to dye things: – If you dye a shirt with blue pigment you are dying it with particles that absorb everything but blue light. – If you mix all pigments together, that means all light will be absorbed and so that object will look black. • When light hits a surface, it can be bent (refracted), bounced (reflected) or absorbed. • Whether light is reflected, refracted or absorbed depends on how it interacts with the atoms of the material. Reflection of Light • When light is returned into the medium it came from we say it is reflected • How light is reflected depends on the roughness of the surface: – Smooth surfaces: non-diffuse reflection – Rougher surfaces: diffuse reflection • Light will always reflect from a surface at an angle equal to the angle it hit the surface at. • Incoming light is called the incident ray • The angle the light strikes the surface at is called the angle of incidence a = angle of incidence a incident ray • Reflected light is called the reflected ray • The angle that light is reflected from a surface is called the angle of reflection • The angle of incidence will always be equal to the angle of reflection. b = angle of reflection b reflected ray Mirrors • When you see yourself in the mirror it is because light is reflected off of you from a light source, hits and is reflected off of the mirror and is interpreted by your eyes to give a virtual image. Virtual image • Convex mirrors: virtual image is smaller • Concave mirrors: virtual image is larger • With concave and convex mirrors the angles of incidence and reflection are still equal, but the surfaces are bent so it changes how your eye interprets the reflected light. • Sometimes objects don’t reflect light in an ‘organized’ way. • Scattering is when light is reflected in all different directions. • Example: – Nitrogen and oxygen scatter the higher frequencies of light (blue and violet) really well. This is why the sky is blue. – Clouds scatter all light equally which is why they appear white. • What is the word used to describe when a wave is bent? refraction • Refraction occurs when a light wave is bent as it moves from one medium to another. • This happens because light travels at different speeds in different mediums. Which ray is the refracted ray? = Ray A = Ray B = Ray C = Angle x3 Which ray is the reflected ray? = Ray A = Ray B = Ray C = Angle x3 Which ray is the incident ray? = Ray A = Ray B = Ray C = Angle x3 Which angle is the angle of incidence? = Angle x1 = Angle x2 = Angle x3 Which angle is the angle of reflection? = Angle x1 = Angle x2 = Angle x3 Which angle is the angle of refraction? = Angle x1 = Angle x2 = Angle x3 • The speed of light is slower in glass, water, air and denser, cooler air. What does it mean when someone is color blind?
Pages to are hidden for
"Visible Light (PowerPoint)"Please download to view full document