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The Electromagnetic spectrum and light Electromagnetic Radiation • Electromagnetic waves: are transverse waves produced by the motion of electrically charged particles. • They do not need a medium and travel in straight lines. • Speed- Can travel though empty space at 300,000km/s or 186,000 miles/sec • Radiation:The transfer of energy by electromagnetic waves. • Photons: Bundles of light energy produced by electron movement Radio Waves • All around us • Long wavelengths and low frequencies. • Radio, TV, cellular phones, cordless phones, Microwaves • Radio waves with the highest frequency and energy. • Communications and microwave ovens! Infrared Radiation • Slightly lower frequency than visible light. • Felt as heat • Infrared lamps keep your french fries warm! IR does not penetrate walls and so does not interfere with other devices in adjoining rooms. Infrared is the most common way for remote controls to command appliances. Visible Radiation (Light) • Or light, is the only part of the electromagnetic spectrum you can see! • Light Energy is produced by the activity of electrons around the nucleus of an atom. • Each different wavelength of light has a different color!! Ultraviolet Radiation • Higher frequency than visible light. • Greater penetrating power! • Helps skin cells produce vitamin D, which is needed for healthy bones and teeth! • Sterilize surgical instruments • Over exposure kills healthy cells!!! • Sagging, dry skin, skin cancer! • Sunblock and sunglasses!!! X Rays • X rays have a shorter wavelength and a higher frequency then ultraviolet radiation. • Higher energy allows X rays to travel through some types of matter such as your skin and muscles. Gamma Rays • Have the highest frequency and are the most penetrating of electromagnetic waves! • They are emitted from the nuclei of radioactive atoms. • Earth receives some from space. • Can be used to kill cancer cells. Electrons • Electrons moving to a higher level gain energy • Electrons that move to a lower level give off electromagnetic energy • Electricity is the movement of electrons, so it comes from the atom. Light Theories • Wave Theory (like dropping a pebble into a pond) • • Electromagnetic Particle • Wave Particle Duality (modern Light Theory)energy of the photon is proportional to its frequency Transverse Waves Mount Moran in Jackson, Wyoming Properties of light • • • • • • • • Luminous- give off their own light (candle) Illuminated- light reflects off of it (moon) Transparent- See through Translucent- Partially see through (blurry) Opaque- not see through (us) Reflection- Light bounces off Refraction- light bends going through Absorption- light that gets absorbed in the material. Types of Reflection • Reflected light is when light is not completely absorbed by an object. • The type of surface affects the type of reflection. • Regular reflection- smooth surface, forms a clear image. (flat mirror) • Diffuse reflection- rough surface, forms a fuzzy image. Reflections • You need 2 things for a reflection: 1. Light 2. A smooth surface 3. The Law of reflection- the angle of reflection is equal to the angle of incidence . (Only applies to smooth surfaces, not rough) MIRRORS (3 Types) • 1. Plane Mirror- or flat mirror creates a virtual image- image that is right-side up and the same size. MIRRORS • 2. Concave mirrormirror with a surface curved inward. • concave mirrors can form either virtual images or real images depending on the position of the object in relation to the focal point. • 3. Convex mirrors- a mirror with a surface that curves outward. • The rays spread out but appear to come from a focal point behind the mirror. • Images formed are always virtual since the reflected rays do not meet. • Because you can see more through convex mirrors, the images always appear smaller and farther away “objects seen in the mirror are closer than they appear” MIRRORS LENSES • A lens is a curved piece of glass that is used to refract light • Convex- thin on top and bottom, thick in the middle • Concave- thick on top and bottom, thin in the middle A corrective lens is a lens worn on or before the eye, used to treat myopia, hyperopia, astigmatism, and presbyopia. The most common types of corrective lenses are eyeglass lenses and contact lenses. Intraocular lenses are also beginning to become common. Myopia (near sightedness) requires biconcave or diverging lenses, whereas hyperopia (far sightedness) requires biconvex or converging lenses. Correct sight with concave lens Lens is to convex • The image is focused in front of the retina • Recall: convex lens focus light (the more convex, the quicker the focus) • Adding glasses with concave lens will spread light out and not let it focus so quickly Correct sight with convex lens Lens to concave • People far sighted see things far well, but do not see things near very well • Recall: concave lens spreads light out • So, • Adding glasses with convex lens will focus light more and not so spread out Image formation • The image through a convex lens appears upside down • The image through a concave lens spreads out the light rays