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x Chapter 2 Using Light Section 1: Waves and the Electromagnetic Spectrum What causes waves? What are the basic properties of waves? What does an electromagnetic wave consist of? What are the waves of the electromagnetic spectrum? x Chapter 2 Using Light Electromagnetic Waves Believe it or not, you are being “showered” all the time, not by rain but by waves. x Chapter 2 Using Light Transverse Waves Waves that move the medium perpendicular to the direction in which the waves travel are called transverse waves. x Chapter 2 Using Light Properties of a Wave Amplitude: The maximum distance that the medium carrying the wave energy moves away from the resting position. x Chapter 2 Using Light Properties of a Wave Wavelength: The distance between two similar parts of a wave. x Chapter 2 Using Light Properties of a Wave Frequency: The number of times a wave passes an area in 1 second. Measured in Hertz (Hz). x Chapter 2 Using Light Properties of a Wave Speed: How fast a wave travels. Measured in kilometers per second (km/s). • Mechanical Waves: The speed can change depending on the medium and the energy. Can be slow or fast, but they can NEVER be as fast as electromagnetic waves. • Electromagnetic Waves: Always travel at “the speed of light” (300,000 km per second in a vacuum). They will slow down a bit when going through mediums like air or glass. x Chapter 2 Using Light Amplitude, Wavelength, and Frequency The basic properties of all waves are amplitude, wavelength, and frequency. x Chapter 2 Using Light Mechanical Waves Mechanical waves are produced when a source of energy passes through a medium. Examples: » Sound » Earthquakes » Ocean waves » “Snapping” a rope x Chapter 2 Using Light What Is an Electromagnetic Wave? • An electromagnetic wave consists of vibrating electric and magnetic fields that move through space at the speed of light. • They do NOT require a medium to travel. x Chapter 2 Using Light What Is the Electromagnetic Spectrum? The electromagnetic spectrum is the complete range of electromagnetic waves placed in order of increasing frequency. x Chapter 2 Using Light Radio Waves • Longest wavelength (and lowest frequency) • Uses the least amount of energy (and is therefore the safest of all E.M. waves) • Used to broadcast FM and AM radio signals • Was once used to broadcast television signals • CB Radio (popular with truck drivers) x Chapter 2 Using Light Microwaves • Used to heat up food in microwave ovens • Also used for cell phone communication x Chapter 2 Using Light Infrared Rays • Usually in the form of invisible heat (stove, fire, etc.) • Can also be used for night vision and thermography x Chapter 2 Using Light Visible Light Makes up a very small part of the very large Electromagnetic Spectrum x Chapter 2 Using Light Visible Light • The human eye can only see wavelengths between 800 nanometers (red light) to 400 nanometers (violet light). • 1 billion nanometers = 1 meter (about 3 feet) x Chapter 2 Using Light Visible Light The main colors of visible light (in order of largest to smallest wavelength): ROY G BIV x Chapter 2 Using Light Visible Light • “White light” is actually all the colors of the visible spectrum blended into one. • Light is separated into the colors of the visible spectrum when it passes through a prism. x Chapter 2 Using Light Ultraviolet (U.V.) Rays • Small amounts are useful to humans (skin can convert UV rays into Vitamin D). • Buy sunblock that has the highest UVA and UVB protection (the best sunblocks contain zinc oxide). • Large amounts are harmful to humans (leading cause of skin cancer). x Chapter 2 Using Light X-Rays • Can pass through most objects except dense matter (like bone or lead). • Excessive exposure can lead to cancer, but getting 3 - 4 X-ray exams a year is considered safe. x Chapter 2 Using Light Gamma Rays • Shortest wavelength (and highest frequency). • Most dangerous of all electromagnetic waves. • In small, concentrated doses, can be used to kill cancer cells. x Chapter 2 Using Light End of Section: Waves and the Electromagnetic Spectrum x Chapter 2 Using Light Section 2: Visible Light and Color How does visible light interact with an object? What determines the color of an opaque object? How is mixing pigments different from mixing colors of light? x Chapter 2 Using Light When Light Strikes an Object When light strikes an object, the light can be reflected, transmitted, or absorbed. Key Term Transmit : to send from one place to another x Chapter 2 Using Light Visible Light Transparent: material that allows light to transmit through it in straight lines »examples: clear glass, clean air Translucent: material that scatters transmitted light as it passes through it »examples: fog, frosted glass Opaque: material that reflects some colors and absorbs other colors; does not allow any light to pass through » examples: walls, mirrors x Chapter 2 Using Light The Color of Objects The color of an opaque object is the color of the light it reflects. x Chapter 2 Using Light Combining Colors : Light . When combined in equal amounts, the three primary colors of light (green, red, and blue) produce white light. The primary colors can also form other colors (example: red and green make yellow). x Chapter 2 Using Light Combining Colors : Pigments • Pigments are found in inks, paints, and dyes. • They absorb some colors while they reflect others. • The primary colors of pigments (magenta, yellow, and cyan) combine in equal amounts to form black. x Chapter 2 Using Light End of Section: Visible Light and Color x Chapter 2 Using Light Section 3: Reflection and Refraction What does the law of reflection state? Why do light rays bend when they enter a new medium at an angle? What determines the types of images formed by convex and concave lenses? x Chapter 2 Using Light The Law Of Reflection When an object or wave hits a surface through which it cannot pass, it reflects (bounces back). x Chapter 2 Using Light Concave Mirrors A mirror with a surface that curves inward like the inside of a bowl is a concave mirror. x Chapter 2 Using Light Concave Lenses A concave lens will make a larger real object look like a smaller “virtual” image. x Chapter 2 Using Light Examples of Concave Mirrors & Lenses Make-Up Mirrors Glasses for Nearsightedness x Chapter 2 Using Light Convex Lenses How can you make this tiny ladybug appear larger? A convex lens will make a small real object look like a larger “virtual” image. x Chapter 2 Using Light Examples of Convex Mirrors & Lenses Blind-spot Mirrors Magnifying Lens Reading Glasses x Chapter 2 Using Light Refraction of Light When light rays enter a medium at an angle, the change in speed causes the rays to bend, or change direction. x Chapter 2 Using Light The Index of Refraction The index of refraction of a medium is a measure of how much light bends as it travels from air into the medium. The table shows the index of refraction of some common mediums. x Chapter 2 Using Light The Index of Refraction Interpreting Data: Which medium causes the greatest change in the direction of a light ray? Diamond causes the greatest change in the direction of a light ray traveling from air. x Chapter 2 Using Light The Index of Refraction Interpreting Data: According to the table, which tends to bend light more: solids or liquids? According to the graph, most solids bend light more than liquids do (quartz is an exception). x Chapter 2 Using Light The Index of Refraction Predicting: Would you expect light to bend if it entered corn oil at an angle after traveling through glycerol? Explain. You would not expect light to bend if it entered corn oil at an angle after traveling through glycerol, because corn oil and glycerol have the same value for the index of refraction. x Chapter 2 Using Light End of Section: Reflection and Refraction x Chapter 2 Using Light Section 4: Seeing Light How do you see objects? What types of lenses are used to correct vision problems? x Chapter 2 Using Light Cross-Section of the Eye ___________________ : Hole through which light enters the eye. ___________________ : Transparent front surface of the eye. ___________________ : Short, thick nerve through which signals travel to the brain from the eye. x Chapter 2 Using Light Cross-Section of the Eye ___________________ : Ring of muscle around the pupil. ___________________ : Curved part of the eye behind the pupil that refracts light. ___________________ : Layer of cells lining the inside of the eyeball. x Chapter 2 Using Light Pupil and Iris The iris (the colored part of the eye) is a ring of muscle that opens and closes depending on how much light needs to enter the eye. The pupil (black hole) is simply the opening made by the iris. x Chapter 2 Using Light Retina The retina is a layer of cells that lines the inside of the eyeball. Contains two types of cells: – Rods • able to see with very little light • can only see black and white images – Cones • respond to colors red, green, and blue • needs bright light to function properly x Chapter 2 Using Light Correcting Vision Concave lenses are used to correct nearsightedness. Convex lenses are used to correct farsightedness. x Chapter 2 Using Light End of Section: Seeing Light x Chapter 2 Using Light Section 5: Optical Tools How are lenses used in cameras, telescopes, and microscopes? x Chapter 2 Using Light Cameras The lens of the camera focuses light to form a real, upsidedown image on film in the back of the camera. x Chapter 2 Using Light Microscopes A microscope uses a combination of lenses to form enlarged images of a tiny object. x Chapter 2 Using Light Telescopes Telescopes use lenses or mirrors to collect and focus light from distant objects. x Chapter 2 Using Light End of Section: Optical Tools