Electromagnetic Spectrum LIGHT Principles of Physics

Electromagnetic Spectrum Waves created by fluctuating electric and magnetic fields Transverse waves Can travel in a vacuum – do not need a medium Travel at the speed of light in a vacuum (c = 300,000,000 m/s) Organized by frequency and wavelength

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5.20x1014 Hz 3.84x1014 Hz 4.82x1014 Hz 5.03x1014 Hz 6.10x1014 Hz 6.59x1014 Hz 7.69x1014 Hz Red Orange Yellow Green Blue Violet

Radio, Micro, and Infrared Waves Longest wavelength and lowest frequency RADIO WAVES ARE NOT SOUND WAVES Provide the signal for communications devices such as: radios, television, cell phones Micro waves are used to cook food Infrared waves are used for TV remote controls, night vision

Ultraviolet, X and Gamma Waves Shortest wavelength, highest frequency Cause damage to human cells because wavelength is close to atomic size Ultraviolet – sun bathing X – used to detect bone damage, baggage screening at airports Gamma – radioactive decay

Visible Light Waves that allow us to see color Red – longest wavelength, lowest frequency (3.84 x 1014 Hz = 384,000,000,000,000 Hz) Violet – smallest wavelength, highest frequency (7.69 x 1014 Hz = 769,000,000,000,000 Hz)

Light Sources Emit light waves Produce light Sun, light bulbs, flames Illuminated Objects Most objects Actually are reflecting light People, plants, rocks, etc. Moon – source or illuminated?

Characteristics of Light Waves Intensity (brightness) = amplitude Large amplitude, a lot of energy (very hot) Small amplitude, less energy (warm)

Characteristics of Light Waves Color = frequency Order of colors = spectrum Primary colors of light – red, green and blue Red light +green light +blue light = white light Different than pigment colors (ink, paint, etc) These reflect light, they are not sources Mixing colors Applet

Light can be reflected or transmitted: Materials Transparent – transmit clearly (clear glass, still water) Translucent – transmit blurry (frosted glass) Opaque – no transmission (light may be reflected or absorbed)

Speed of light in a vacuum = c = 299,792,458 m/s = 2.99792458 x 108 m/s ≈ 3.00 x 108 m/s Speed of light in any other material depends on optical density (ability of a material to transmit light) Greater optical density, more light slows down Air c / 1.003 ≈ 3.00 x 108 m/s Water c/1.33 Diamond c/2.42

Scientific Notation Put a decimal after the first non-zero number and drop any zeroes Determine the power of ten by counting the places before of after the decimal Show the places before or after the decimal using an exponent. Use a negative on your exponent if the decimal is before the number 1. Ex: 300,000,000 → 3.0 0.000345 → 3.45 2. Ex: 300,000,000 → 3.0 8 places after 0.000345 → 3.45 4 places before Ex: 300,000,000 → 3.0 x108 0.000345 → 3.45 x 10-4