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  • Light

    small portion of the electromagnetic spectrum that our eyes are capable of seeing

    Electromagnetic Spectrum

    complete range of radiation produced by accelerated charged particles

    Cosmic, Gamma, Ultraviolet, and X rays

    high frequency and harmful

    Light, Infrared, and Radio Waves

    low frequency and harmless

    Velocity of Light

    all travel at 3x10^8 m/s

    Light year

    distance that light travels in one year, used to measure extremely large distances like the distance to stars

    Production of Light

    all atoms have electrons in distinct energy levels. When atoms absorb energy, electrons move to higher energy levels. In all substances, the electrons return to lower energy levels and give off energy in form of light

    3 means of atoms becoming excited

    heat which occurs in a regular incandescent bulb, electricity through a gas which occurs in a fluorescent light bulb, and light shining on a substance that glows which occurs in the white phosphorous in the inside of the fluorescent tubes

    Continuous Spectrum

    all the colors of white light when viewed through a spectroscope, ROYGBIV

    Bright Line Spectra

    distinct lines of color (wavelength) given off an element when viewed through a microscope

    Color of Objects

    the color we see due to the wavelengths reflected. Blue objects reflect blue wavelengths and red objects reflect red wavelengths, etc. Black objects absorb light and white objects reflect all wavelengths

    Primary Colors

    when mixed they produce white: blue, green, and red

    Primary Pigments

    yellow, cyan, magenta

    Luminous Objects

    give off their own light, example: sun, light bulb, candle flame

    Illuminated Objects

    reflect light, everything we see that isn't luminous

    Luminous Intensity

    brightness of the source, measured in candles or candle power

    Luminous flux

    brightness of the source, more commonly used than luminous intensity, measured in lumens

    Illumincance (Illumination)

    the amount of light that falls on a surface, depends upon the brightness of the source and how far the surface is from the source

    Illuminance Calulation


    Transparent Objects

    allow light to pass through without distortion, example: clear glass or air

    Translucent Objects

    allow light to pass through but the light is distorted, example: frosted glass

    Opaque Objects

    do not allow light to pass through, example: solid wall

    Reflection of Light

    light rays will bounce off a surface at the same angle they struck

    Law of Reflection

    angle of incidence = angle of reflection

    Diffuse Reflection

    reflection off a rough surface, no image is seen

    Regular Reflection

    reflection off a smooth surface like mirrors, images are seen


    breaking of white light into its colors when it passes through a prism, it produces a continuous spectrum (ROYGBIV)

    Rainbow in the Sky

    produced when tiny water droplets in the sky act as prisms and disperse the light

    Real Image

    can be projected onto a screen and is always upside down if the object is right side up. Image distance is positive, magnification and height are negative

    Virtual Image

    cannot be projected and is only seen on the mirror or lens, they are always right side up. Image distance is negative, magnification and height are positive

    Refraction of Light

    as light passes from one medium to another, it changes velocity. If the light enters the new medium at an angle, the light ray will bend. The degree to which it bends upon the optical densities of the media involved

    Law of Refractions

    as light pases from less dense medium into more dense medium, it will blend towards to the normal. If the light ray passes from more dense to less dense, it bends away from the normal

    Index of Refraction

    numerical value for the optical density of the substance

    Total Internal Refraction

    when a light passes from more dense medium toward less dense medium, if the angle is large enough, it wil not refract out of the substance but rather reflects inward

    Dual Nature of Light

    light has the properties of both particles and waves

    Photo Electric Theory

    when light strikes a thin foil, electrons are emmitted off the backside of the foil as if a collision took place, this effect could not be explained by the wave theory and was a conclusive support for the particle theory

    Concave Mirrors

    curved inward

    Convex Mirrors

    focal length is negative

    Flashlights and spotlihts

    they contain a concave or spherical mirror or parabolic mirror, the light source is placed at the focal point and the light shines back on the mirror and reflects as a beam

    Converging (convex) lens

    thicker in the middle and thinner on the ends, example: magnifying glass

    Diverging (concave) lens

    thinner in the middle and thicker on the ends

    Compound lens system

    (microscope or telescope) contains at least 2 lenses, the real image is produced by the first lens (objective lens) becomes the object for the second lens (the eyepiece) that magnifies it as a larger virtual image

    Human Eye

    contains a flexible converging lens surrounded by muscles, the muscles contract to focus near and relax to focus far, a real image is focused on the black of the eye (retina)

    Nearsightedness (myopia)

    the lens can focus near but not far, most young people who need glasses are nearsighted, corrected with a diverging lens

    Farsightedness (hyperopia)

    the lens canot focus near, almost all people become this as they age and need reading glasses, converted with a converging lens


    change in density above road is caused by heat, causes the light to bend and never reach the road

    Sun not where it appears?

    light left sun 8 minutes ago, the light is going to the atmosphere, different in n's and the light bends. The light bends from vacuum to air, the n changes

    Scattering (blue sky)

    blue wavelengths reflect off air molecules and scatter in all directions

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