Light 12/8/15 Light Basics Light is the range of frequencies emitted by different objects Many different objects emit light, light bulbs, the sun. ect. Light basics Light travels in a straight line This has lead to the ray model of light. This is useful for taking about reflection and refraction Light basics The speed of light is a constant in a vacuum This speed is 299,792,458 m/s. However for class we will just use 3X10^8 m/s Albert Michelson First American to win the Nobel Prize in a science Experimentally determined the speed of light of 299,799,600 m/s Disproved idea of the ether Wavelength and Frequency Because speed of a wave is constant, if we change wavelength frequency must change as well. If yellow light has a wavelength of 556 nanometers, what is its frequency? EM Spectrum Since light can have different wavelengths and frequencies different types of light exist. EM Spectrum With the wavelength of light you had for your practice problem, research this type of light and find where it is on the spectrum, and its practical application. Illuminance How illuminated an object is Determined by luminous flux(lumens)/ 4*pi*r^2 Unit is lux, lx Light decreases by 1/r^2 Practice problem A lamp is moved from.3 to.9 m away from a book. What is the illumination on the page, before and after the movement? Luminous Intensity The intensity of light at 1m Lumens/4*pi Unit is candela (candle power) Doppler effect Doppler effect still works for light. Equation is the same except velocity is the speed of light Laser safety Four classes of lasers 1:safest-4:most dangerous Class four may ignite combustible materials Reflection What did you see in the lab you just did? Reflection How can you crate a mathematical formula based on what you saw? Reflection We dont see light unless the light gets reflected so we can see it. Reflection Now place your laser on the edge of the table and make a system of mirrors to hit an object at a different point on your table. Real world applications Mirrors: use use one everyday Optical fibers: fibers are made out of glass and reflect images back so we can see them Law of Reflection Last Wednesday we learned about the law of reflection what does the Law of Reflection mean? How can this be used by multiple mirrors? Mirrors As you saw on Wednesday we have used mirrors that you are used to in your everyday life. How can we figure out where an image will appear on the mirror? Ray model In the ray model we draw lines to indicate where light is travelling. Lets take an example of a person taking a selfie. Ray model use 1: parallel ray. This ray is parallel to an object. 1: parallel ray. This ray is parallel to an object. 2: focus ray. Ray travels toward and passes through focal point of mirror. For plane mirrors this ray hits mirror and goes towards the observer Where rays meet is where an image is. Example for a candle Mr. Give an example of ray diagrams for a candle in his plane mirror. You will do this three times in your group. Parts of images Do=distance of object Di=distance of image F=focal length Ho=height of object Hi=height of image Concave mirrors Concave mirrors are one type of curved mirror. You will be performing a lab to find the relationship between the distance an object is and the image it creates. Concave and convex mirrors 1/(focal length)= 1/(distance image)+1/(distance object) Magnification=(height image)/(height object) (Height image)/(height object)=-(distance image)/(distance object) Practice problem A concave mirror has a focal length of.1m and an object is placed at.2 meters and is.1 m high. Where is he image located, and what is the height of this new image? Practice problems In your group work on this problem: The focal length of a concave mirror is.4m. If we place a mirror at.5 meters, Darw a picture and find the the distance of the image. If the the height of the object is.1m, what is the height of the image. Real vs. imaginary image Real images can be found on a screen not just in a mirror. Imaginary images can only be seen in a mirror. What did you see when you brought the candle inside the focal point Convex mirrors Convex mirrors have the opposite look of a concave mirror No real images are created by a convex mirrors Convex mirrors Convex mirrors create an upright imaginary image These can be used in security mirrors. Refraction When light passes into another medium light will refract Straw and water Refraction Different materials will have a different index of refraction Index of refraction n is equal to the speed of light divided by lights speed in a particular material N=Vc/V Index of refraction Common indices of refraction: Vacuum=1.00Water=1.33Quartz=1.54Diamond=2.42 Snells law Snells law tells us the relationship between index of refraction and the angle our light will travel. N1*sin(theta1)=n2*sin(theta2) Practice A light is incident on a block of glass with an angle of 10*, If the refracted angle is 5* what is the index of refraction of the material? Snells law Today we will investigate the index of refraction of water.