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Light and the Electromagnetic Spectrum: Chapter 13 and 14 Electromagnetic Waves •Do NOT need matter in order to move •Can travel through space (in a vacuum) where matter is not present •Transfer energy between vibrating electric and magnetic fields •The electric and magnetic waves are at right angles to the direction of the wave: transverse waves •Scientists describe them as both wavelike and particlelike Production of the wave •Electrons are needed to produce the wave, they change speed and direction as they move in their orbits •They also produce electric and magnetic fields that vibrate (move back and forth) •The speed of the waves is 300 million meters per second (the speed of light). It takes light from the sun about 8 minutes to reach the Earth The Electromagnetic Spectrum •Arranged in order of wavelength and frequency •Waves with the longest wavelength have the lowest frequency •The spectrum ranges from very long wavelength, low frequency to short wavelength, high frequency •The amount of energy increases with frequency •The only portion that is visible is light, the rest is invisible 1. Radio Waves Longest frequency and lowest wavelength… not much energy 2. Produced when charged particles move back and forth in instruments (antennae) 3. They transmit information from the broadcasting station to the antenna of your radio or TV, AM (Amplitude Modulation) or FM (Frequency Modulation) 4. Your TV uses AM waves for the picture and FM waves for the sound 5. Radio waves are also used in medicine. MRI (Magnetic Resonance Imaging) shows pictures of body parts such as the brain Microwaves highest frequency radio waves •Used for cooking food, microwaves pass through glass and plastic and are absorbed by the food. Metals absorb microwaves and an electric current can form. •Radar: short wavelength microwaves, used to locate objects and monitor speed… also used for communication (cell phones) because they are not easily blocked by tree’s, mountains and buildings. Infrared Waves frequency lower than visible light •Cannot be seen, but can be felt •Warmer objects give off more heat than cooler objects •Used to keep food hot, relieve sore muscles, dry hair The Visible Spectrum •Waves we can see: Red, Orange, Yellow, Green, Blue, Indigo, Violet •Red has longest wavelength & Violet has shortest wavelength •Is essential for photosynthesis •Luminous object: anything that can give off its own light, produces its own light, the sun •Illuminated object: you can see it because it is lit up, the moon Types of Light •Incandescent Light: regular light bulb, light is produced from heat •Fluorescent Light: bulb above you, produces little heat, energy efficient, electrons pass through gas molecules •Neon Light: Cool light, electrons pass through different gases producing different colored light Ultraviolet Rays frequency higher than visible light •Energy enough to damage and kill living cells •UV lamps used to kill germs in hospitals •Can be seen by insects and felt as sunburn on humans •Cause your skin cells to produce vitamin D X-Rays •Frequency above ultraviolet •Bones absorbs X-Rays which is why we can see the bones •Overexposure can cause defects to cells. Gamma Rays •Most dangerous high frequency waves •Can travel through 3 meters of concrete •Used for cancer treatment LIGHT Mirror Types: Concave mirror – a mirror that curves inward, if the image is close it is right side up; if the image is farther away you see it upside down. Example: looking into a spoon. Convex mirror – the surface curves outward; the image is right side up and smaller. Example: rear view mirror. • • • • When light strikes any form of matter, light is either transmitted, absorbed, or reflected. We see any colors that have not been absorbed by the object. Transparent – where light goes through easily (glass, water, air…) Translucent – transmits light but no details. (wax paper; frosted glass) Opaque – when no light is transmitted. (wood, metal, etc…) The Human Eye: Steps to sight Light enters pupil Goes through the Iris Is refracted (by the cornea) and focused on the retina The Lens focuses objects Optic nerve goes to brain Rods and Cones •Rods: sensitive to light and dark •Cones: responsible for seeing color, each cone is sensitive to a particular color. •Colorblindness: when cones are not receptive to colors, most often red and green, rare, but more common in males than females. Types of sightedness •Nearsightedness – a person can see things that are near but not things at a distance. •Farsightedness – a person can see things at a distance but not things that are near.