Light Electromagnetic and Visible Spectrum

Electromagnetic Waves Consist of changing magnetic and electric fields moving through space at the speed of light (3.0 x 10 8 m/s) Consist of changing magnetic and electric fields moving through space at the speed of light (3.0 x 10 8 m/s) Are produced by vibrating charged particles Are produced by vibrating charged particles Do not require a medium Do not require a medium

Electromagnetic Spectrum Range of frequencies of electromagnetic waves Range of frequencies of electromagnetic waves As frequency increases, wavelength decreases As frequency increases, wavelength decreases As frequency increases, energy of a wave increases As frequency increases, energy of a wave increases

Electromagnetic Spectrum The light we can see is only a small part of all light. The light we can see is only a small part of all light. The whole range is called the electromagnetic spectrum and visible light is in the middle of it. The whole range is called the electromagnetic spectrum and visible light is in the middle of it. On the low energy end of the spectrum are radio waves. On the high energy end are gamma rays. On the low energy end of the spectrum are radio waves. On the high energy end are gamma rays.

E-M Spectrum Radio waves Microwaves InfraredUltraviolet Visible X-rays Gamma-rays

Radio Waves have the lowest frequency and the longest wavelength. have the lowest frequency and the longest wavelength. includes TV waves, which are “vhf” (very high frequency) or “uhf” (ultra high frequency), and radar waves, with highest frequency includes TV waves, which are “vhf” (very high frequency) or “uhf” (ultra high frequency), and radar waves, with highest frequency Each radio station broadcasts at a set frequency. Each radio station broadcasts at a set frequency. Sound waves are converted into electrical signals and change (modulate) the carrier waves. Sound waves are converted into electrical signals and change (modulate) the carrier waves. am - amplitude modulation fm - frequency modulation In receiver antennae, electrons are made to vibrate sympathetically at set frequency (concept of resonance) In receiver antennae, electrons are made to vibrate sympathetically at set frequency (concept of resonance)

Microwaves Penetrate food evenly. Penetrate food evenly. Match the natural frequencies of large molecules, which vibrate and produce heat to cook food from inside. Match the natural frequencies of large molecules, which vibrate and produce heat to cook food from inside. Air molecules in the oven are too small to be excited, and microwaves also have no effect on ceramics, plastic, or glass. Air molecules in the oven are too small to be excited, and microwaves also have no effect on ceramics, plastic, or glass. Metals reflect microwaves. Metals reflect microwaves. Droplets of water absorb microwaves and form steam. Droplets of water absorb microwaves and form steam. When food is removed from an oven, molecules continue to vibrate, so “stand” time is included in recipes. When food is removed from an oven, molecules continue to vibrate, so “stand” time is included in recipes.

Infrared Atoms and molecules vibrate to produce infrared waves. Atoms and molecules vibrate to produce infrared waves. All objects emit infrared waves in the form of heat. All objects emit infrared waves in the form of heat. uses for infrared waves: uses for infrared waves: Sun, fire, radiation, heat lamps used in restaurants

Visible Light electromagnetic radiation to which human eyes are sensitive. electromagnetic radiation to which human eyes are sensitive. makes up less than % of electromagnetic spectrum makes up less than % of electromagnetic spectrum different frequencies are seen as colors. different frequencies are seen as colors. red – lowest frequency and lowest energy violet – highest frequency and highest energy

Visible light is that portion of the electromagnetic spectrum which stimulates the retina of the human eye. Visible spectrum wavelengths range from about 400 nm (violet) to 760 nm (red). Light travels at about 3 x 10 8 m/s through empty space and slightly slower through air. Remember that for all waves, v = f.

WHITE light is a combination of ALL the colors of the visible spectrum. Red, orange, yellow, green, blue, indigo, violet is the order of increasing frequency or decreasing wavelength. Frequencies directly above this spectrum are ultraviolet. Frequencies directly below this spectrum are infrared.

Ultraviolet Overexposure can cause sunburns and skin cancer Overexposure can cause sunburns and skin cancer uses: medicine to sterilize surgical instruments by killing bacteria uses: medicine to sterilize surgical instruments by killing bacteria higher UV frequencies are blocked by gas in atmosphere higher UV frequencies are blocked by gas in atmosphere Fact or Fiction: Sunlight through a window can give you a sunburn? Fact or Fiction: Sunlight through a window can give you a sunburn? Fiction- Ultraviolet rays can not penetrate through a window. It is infrared waves that are passing through and that is why it is warm.

X-rays discovered by Wilhelm Roentgen discovered by Wilhelm Roentgen produced by greatest acceleration of electrons. produced by greatest acceleration of electrons. uses: x-ray machine for bodies or teeth, to check luggage at airports uses: x-ray machine for bodies or teeth, to check luggage at airports

Gamma Rays highest energy and greatest penetrating power highest energy and greatest penetrating power produced by nuclear reactions, including decay of radioactive atoms and nuclear explosions produced by nuclear reactions, including decay of radioactive atoms and nuclear explosions kills cancer cells before it kills healthy cells kills cancer cells before it kills healthy cells uses: removing decay-causing bacteria from many foodstuffs or preventing fruit and vegetables from sprouting to maintain freshness and flavor uses: removing decay-causing bacteria from many foodstuffs or preventing fruit and vegetables from sprouting to maintain freshness and flavor