Early Work - Feb. 20 - Rock Creek Schools

Early Work - Feb. 20 - Rock Creek Schools

Early Work Feb. 20 Explain the uses of light Definitions from Ch. 16 Test Back Ch 16

Light Light Light is the range of frequencies of electromagnetic waves that stimulates the retina of the eye Light

Wavelength range 400 nm violet 700 nm red ROYGBIV Light travels in straight lines Which makes shadows possible

Light Light behaves like both a wave and a particle Use ray model to model the path of light (which thinks of it as a particle) Speed of Light Ole Roemer (1644 1710)

First to determine light travels at a measurable speed Calculated velocity based on distance and time (Ios orbit is 42.5 hours) c = 299, 792, 458 m/s c = 3 x 108 m/s

Practice Problems P 376: 1, 4 Early Work Feb. 22 Explain how Roemer first calculated the speed of light. Turn in vocab and PP 1, 4

Sources of Light A luminous body emits light waves The sun An illuminated body reflects light waves The moon

Luminous Flux Luminous Flux, P The rate at which visible light is emitted from a source Measured in lumens, lm A standard 100-watt light bulb emits 1750 lm Illuminance

Illuminance, E The rate at which light falls on a surface Something we can use more than luminous flux Measured in lumens per square meter, lm/m2

Or lux, lx Since light is emitted radially, use 4r2 to find the surface area of a sphere Illuminance Two ways to increase illumination

Get a brighter source increase luminous flux Move object closer Both represented with: P E

2 4 d Luminous Intensity Luminous Intensity The luminous flux that falls on 1 square meter of a sphere 1 meter in radius

P P E 2 4 d 4 Measured in candela, cd

SI unit for all light intensity Example What is the illumination on your desktop if it is lighted by a 1750-lm lamp that is 2.50 m above your desk?

Practice Problems 6, 7, 9 11 16.2 Light and Matter Materials Transparent materials

Light waves are transmitted without distortion Translucent materials Light waves are transmitted with distortion Opaque materials Transmit no light, or reflect all light

Color Isaac Newton, at 24, did experiments on what he called the spectrum after observing it from a prism Through it unevenness in the glass Color by Addition White light can be formed

from the correct combination of red, green, and blue lights Primary Colors red, green, and blue Used in TVs Secondary Colors purple

(magenta), cyan, yellow Red and green yellow Red and blue magenta Blue and green cyan Color by Addition If you have a color made by two other colors, then you

already have two of the three colors needed to make white light. Complementary Colors a primary and a secondary that produce white light Magenta and green Yellow and blue

Cyan and red Colors by Subtraction Dye a molecule that absorbs certain wavelengths and transmits or reflects others Pigment a colored material that absorbs certain colors and transmits or reflects

others Difference is a pigment is larger and can be seen with a microscope Often pigments are ground inorganic materials Colors by Subtraction Primary Pigment absorbs one primary color

Yellow absorbs blue and reflects red and green Cyan absorbs red and reflects blue and green Magenta absorbs green and reflects blue and red Colors by Subtraction

Secondary Pigment absorbs two primary colors and reflects one Red absorbs green and blue Green absorbs red and blue Blue absorbs red and green Note Primary pigments are secondary lights

Primary lights are secondary pigments Mixing Pigments If the primary pigment yellow (which absorbs blue) is mixed with the secondary pigment blue (which absorbs everything but), then you get black because no wavelength is being reflected

Remember, when you mix light you get white Bkwk P 389: 2 21, 24 44 Hmwk due Wed. Feb. 28 Ch. 16 Test Feb. 28

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