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Light Light is an electromagnetic wave No medium is necessary to travel Has all of the characteristics of a wave All electromagnetic waves are transverse waves Light can also behave as a particle Light is only one type of electromagnetic wave but all electromagnetic waves do not need a medium to travel through Electromagnetic Waves produced by charges that are accelerating rapidly charging made up of vibrating electric and magnetic fields how do electromagnetic waves travel the charging electric field creates the magnetic field the changing magnetic field creates the electric field Speed Electromagnetic Waves all electromagnetic waves travel at the same speed in a vacuum speed v c 3 00 x 10 8 m s c 300 000 000 m s if all electromagnetic waves travel at the same speed what makes them different from one another wavelength Electromagnetic Spectrum Electromagnetic waves are grouped by wavelength or frequency Visible light is only a small portion of the spectrum high frequency waves carry more energy than low classification of electromagnetic waves according to frequency lowest frequency of light we can see appears red highest frequency of light we can see appears violet higher frequency of light is ultraviolet more energetic and causes sunburn beyond are x ray and gamma ray no sharp boundary between regions Frequency vs Wavelength as frequency goes up wavelength goes down Visible Light what the wave values mean wavelength or frequency color frequency energy amplitude intensity brightness Wavelength and color your retina chemically responds to wavelengths between 400 nm and 700 nm 1 nm 1 nano meter or one billionth of a meter 1 nm 1 000 000 000 nm Other colors your retina does not respond to other wavelengths shorter than 400nm longer than 700nm When light encounters matter light behaves like a particle called a photon when it interacts with matter light pushes charged particles three things can happen light goes straight through transmission light bounces off reflection chp 14 light is absorbed absorption Transparent and Opaque Materials how does light penetrate transparent material such as glass electrons or molecules in the glass are forced into vibration energy is momentarily absorbed and vibrates the electrons in the glass this vibrating electron either emits a photon or transfers the energy as heat time delay between absorption and reemission of energy of vibrating electrons results in a lower average speed of light through a transparent material Transmission Absorption Transmission only the electrons move the light doesn t lose energy light travels slower in the medium Absorption the nuclei also move stealing energy from the light the substance heats up infrared light is very good at heating things Average speed of light through different materials vacuum c 300 000 000 m s atmosphere slightly less than c but rounded off to c water 0 75 c 3 4 c glass 0 67 c 2 3 c diamond 0 41 c How to slow down light light moves slower in any material as compared to in vacuum the speed depends on the type of medium recall speed wavelength x frequency what changes wavelength frequency or both when light crosses a boundary from one medium to other wavelength changes frequency does not change Color objects reflect light of some frequencies and absorb the rest rose petals absorb most of the light and reflect red objects that absorb light and reflect none appear black object can reflect only those frequencies present in the illuminating light color of transparent object depends on the color of light it transmits colored glass is warmed due to energy of absorbed light illuminating the glass additive primary colors red green blue complementary colors magenta red blue cyan blue green and yellow red green Why is the sky blue scattering of sunlight by atoms in the atmosphere such as nitrogen and oxygen atoms behave as tiny tuning forks reacting to the energy of the sun vibration of the atom causes photons to be emitted from the atom discrete frequencies of light violet is scattered the most by nitrogen and oxygen then blue green yellow orange and red blue sky varies with atmospheric conditions low moister very blue sky high amount of dust particles causes a white appearance Why sunsets are red

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Longwood PHYS 103 - Light

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