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Physics - Dr. Naumoff Review – Chapters 25-29. Name_________________________________ Date _________________________________ To be shown to your instructor at the end of the period. 1. (Chapter 25) In the picture below a. What is the length labeled “a” called? _____Wavelength (or Period if x-axis in time) b. What is the length labeled “b” called? _____ Wavelength (or Period if x-axis in time) c. What is the length labeled “c” called? ______Amplitude d. What is the point labeled “d” called? ______Trough e. What is the point labeled “e” called? _______Crest 2. A wave is generated by a source with a frequency of 30Hz. The distance between wave crests is 0.25m. What is the speed of the wave? Please show all work and units. V=f*λ V = 30 * .25 = 30/4 = 7.5 m/s 3. How is the frequency of a wave related to its period? The frequency of a wave is the inverse of its period: F = 1/T where T is the wave’s period. 4. How is the period of a wave related to its frequency? The period of a wave is the inverse of its frequency: T = 1/F where F is the wave’s frequency. 5. What is the difference between a transverse wave and a longitudinal wave? In a transverse wave the medium (particles of matter in the wave) move perpendicular to the motion of the wave. In a longitudinal wave the medium (particles of matter in the wave) move in parallel to the motion of the wave. 6. (chapters 27 and 28)What does all electromagnetic radiation have in common? They are all transverse waves. 7. What makes different types of electromagnetic radiation different? _ The frequency and wavelength of the waves. (Chapter 26) 8. Define the following terms. Please use complete sentences. a. Beats: A throbbing in the loudness of sound caused by interference when two tones of slightly different frequencies are sounded together. b. Compression: A pulse of compressed air or other matter. c. Forced Vibration: The vibration of an object that is made to vibrate by another vibrating object that is nearby. The sounding board in a musical instrument amplifies the sound through forced vibration. d. Infrasonic: The term applied to sound pitch too low to be heard by the human ear, that is, below 20 Hz. e. Natural Frequency: A frequency at which an elastic object will vibrate. Minimum energy is required to continue at that frequency. Also called resonant frequency. f. Pitch: The term that refers to how high or low sound appear to be. g. Rarefaction : A disturbance in the air (or matter) in which the pressure is lowered. The opposite of compression. h. Resonance: A phenomenon that occurs when the frequency of forced vibrations on an object matches the objects natural frequency, resulting in a dramatic increase in amplitude. i. Ultrasonic: The term applied to sound pitch that is too high to be heard by the human ear, that is, above 20,000 Hz. 9. What causes all sound waves? Vibrations of material objects. 10.What can sound waves travel through? Mater that is solid, liquid or gas. 11.What cannot sound waves travel through? Empty Space or a vacuum. 12.Explain what causes the sounding board on a guitar to amplify the sound of the strings? The strings cause a forced vibration in the sound board resulting in an amplification of the sound since the sound board has a greater surface area than the strings. 13.Will sound travel faster through air or steel? Why? Steel because the molecules that need to vibrate for sound to travel through are closer together in steel than they are in air. 14.What happens to the speed of sound in air as the air temperature increases? The speed of sound increases when the temperature of the environment increases. 15.By how much does the speed of sound increase for every increase of 1oC in temperature? The speed of sound increases in speed by 0.6 m/s for every 1 °C increase in temperature. 16.At 0 oC sound travels through air a 330 ms . How fast does it travel at 5 oC? V2 = V1 + 0.6*ΔT = 330 m/s + 0.6 * 5 oC = 330 + 3 = 333 m/s 17.A device produces two tones, one at 400Hz and 1 at 410Hz. What is the beat frequency? FB = F 2 - F1 FB= 410 – 400 = 10 Hz. 18.What 19.How is important in creating resonance? A forced vibration at the natural frequency of the object. do noise cancelling earphones work? In coming noise is recorded , shifted by 180 degrees (or ½ wavelength) and then added to the noise prior to reaching the speakers of the headphones. This is an example of destructive interference. 20.If you have two identical sources producing the same tone, why does destructive interference occur when the path lengths from the two sources to the observer differ by ½ of a wavelength? Because the sign of the wave that is shifted by ½ wavelength becomes the exact opposite on the un-shifted wave. When the two waves are added they cancel each other (+1 +-1 =0). Chapter 27 21.Define the following terms. Please use complete sentences. a. Photon: A photon is a “particle” of light. b. Electromagnetic wave : A wave that is partially electric and partially magnetic and carries energy. It is emitted by vibrating electrons. c. Light-year: The distance light travels in one year in a vacuum traveling at 3 x 108 meters/sec. d. Opaque : The term applied to materials that absorb light without reemission, and consequently do not allow light through them. e. Penumbra: A partial shadow that appears where light from part of a source is blocked and light from another part of the source is not blocked. f. Polarization: The aligning of vibrations in a transverse wave, usually by filtering out waves of other directions. g. Ray: A thin beam of light. h. Shadow : A shaded region that results when light falls on an object and thus cannot reach into a region on the far side of the object. i. Transparent : The term applied to materials that allow light to pass through them in straight lines. j. Ultraviolet: Electromagnetic waves of frequencies higher than those of violet. Cannot be seen by human eyes. k. Umbra : The darker part of a shadow where all the light is blocked. 22.What does all electromagnetic radiation have in common? All electromagnetic radiation is composed of transverse waves. 23.What makes different types of electromagnetic radiation different? Electromagnetic radiation types differ by their wavelength and frequencies. 24.How does a penumbra occur? As an object moves between a light source and a viewing surface (screen) the object partially blocks some of the light from that source. However, some of the light from the source gets around the object and fills in part of the shadow. This results in a fuzzy shadow as opposed to a distinct total shadow (umbra) when the light is completely blocked by an object. 25.Describe how ultraviolet electromagnetic radiation is kept from passing through glass. Light is transmitted through glass by exciting electrons in the glass. Since the atoms in glass have a natural frequency (they are resonant) in the ultraviolet range, the atoms in the glass vibrate without exciting the electrons. While these atoms bump into each other they give up their energy to each other Within the glass, thereby warming it up not allowing these frequencies pass through. a. Explain why visible light passes through glass. Light is transmitted through glass by exciting the electrons in the atoms on the surface of the glass. As these electrons emit the light photons, they excite electrons on the inner portion of the glass. This process continues until the electrons in the atoms on the other side of the pane of glass finally emit their photons into the area enclosed completing the journey through the glass. This process is also known as the “Gulp and Burp” transmission of light. 26.Explain why infrared electromagnetic radiation is kept from passing through glass? Infrared radiation vibrates not only the electrons, but the entire structure of the glass. The vibration of the structure increases the internal energy of it warming it up thereby preventing these frequencies from passing through. 27.How do polaroid sunglasses block out glare caused by horizontal surfaces? Since light is composed of transverse waves (waves whose particles vibrate perpendicular to the direction of wave travel), polarized sunglasses are made with filters that only pass light that vibrate in the vertical direction. 28.What causes all electromagnetic radiation? The vibration of Electrons. Chapter 28 1. Define the following terms. Please use complete sentences. a. Spectrum: For sunlight and other white light, the spread of colors seen when light is passes through a prism or diffraction grating. b. Line spectrum: The pattern of distinct lines of color corresponding to particular wavelengths that are seen in a spectroscope when hot gas is viewed. c. White light: Light, such as sunlight, that is a combination of all colors. Under white light, white objects appear white and colored objects appear in their individual colors. d. Additive primary colors: Red, Green, Blue light. When these three colors of light are added together, they produce white light. e. Complementary colors: Two colors of light beams that when added together appear white. f. Pigment : A material that selectively absorbs colored light. g. Scatter : To absorb sound or light and reemit it in all directions. h. Spectroscope: An instrument used to separate the light emanating from a hot gas or other light source into its constituent frequencies (colors) i. Subtractive primary colors: The colors of magenta, yellow and cyan. These are the three colors most useful in color mixing by subtraction (Paints and dyes). 2. Explain why the sky is blue? The sky is blue because the O2 and N2 in the atmosphere scatters the blue light the most during the daylight hours. 3. Why is water greenish blue? Water absorbs Red & infrared leaving cyan, that color that appears greenish blue. 4. What is the brightest color in sunlight? YellowGreen because our eyes are most sensitive to that portion of the visible spectrum. 5. What are the three primary colors of light addition? Red, Green, Blue 6. What color is produced when red and blue lights shine on a white surface? Magenta. 7. What is the complementary color of blue Red. 8. What are the three paint colors useful for color subtraction? Magenta, Yellow and cyan. 9. What happens to most of the ultraviolet radiation that comes to earth from the sun? Most of it is blocked by the Earth’s atmosphere but some does get through and reaches the surface. 10. How does the daytime sky on the moon look? Black 11. When a solid sample of an element is heated until it glows what colors of light are given off? First Infrared which we cannot see, then Red, then Orange, then Yellow then bluish until it gives off white light if the heat source is strong enough to raise the object’s temperature high enough to emit white light. 12. Explain why sunrises and sunsets are red. At the time of sunrise and sunset, the sunlight must pass through more and more atmosphere that scatters more and more blue light leaving less and less to reach the surface of the Earth. The light “left over to reach the Earth’s surface” contains more red light as compared to blue thereby turning the sky more red. Chapter 29 – 1. Define the following terms. Please use complete sentences. a. Angle of incidence: The angle between an incident ray of light and the normal (perpendicular line) to a surface. b. Angle of reflection : The angle between a reflected ray of light and the normal (perpendicular line) to a surface. c. Critical angle: The minimum angle of incidence for which a light ray is totally reflected within a medium. d. Dispersion : The separation of light into their colors arranged according to their frequency by interaction with a prism or diffraction grating. e. Law of reflection : The Angle of Incidence for a wave that strikes a surface is equal to the Angle of Reflection for that wave. This is true for both partially and totally reflected waves. f. Normal: The line perpendicular to a surface that the Angle of Incidence and Reflection is measured from. g. Reflection: The bouncing back of a particle or wave that strikes the boundary between two media. h. Refraction: The change in direction of a wave as it crosses the boundary between two media in which the wave travels at different speeds. i. Total internal reflection: The 100% reflection (with no transmission) of light that strikes the boundary between two media at an angle greater than the critical angle. j. Virtual image: An image formed through refraction that can be seen by an observer but cannot be projected on a screen because light from the object does not come from to a focus. k. Wave front: The crest, trough or any continuous portion of a two- dimensional or threedimensional wave in which vibrations are all the same way at the same time. 2. How does reflection of sound compare with the reflection of light? Sound and light reflect in the same way, they both obey the law of reflection. Therefore, the angle of reflection for sound incident on a boundary at the same angle of incidence as a light wave would be identical to that of light. 3. Which color in the visible spectrum is bent the most when it moves between different media? Violet. 4. Which color in the visible spectrum is bent the least when it moves between different media? Red. 5. In the space below draw a diagram of a light ray going from air to water. Air ׀ _________ ___________׀ Water ׀ 6. In the space below draw a diagram of a light ray going from water to air. Water ׀ _________ ___________׀ Air ׀ 7. What is the index of refraction n? The ratio of the speed of light in a vacuum to the speed of light in a medium. n = Light speed in Vacuum / Light speed in a medium 8. Light moves through a substance with a speed of 2.2×108 meters per second. What is the index of refraction for that substance? n = Light speed in Vacuum /Light speed in a medium = 3 x 108 / 2.2 x 108 = 1.363636 9. A light ray transitions from air into a substance with a refractive index of 3.0. If the angle of incidence is 25°, what is the angle of refraction? This is an application of Snell’s Law which states that: n1 x sin θinc = n2 sin θrefrac 1 x sin (25) = 3 x sin θ2 Sin-1 (θ2) = 1/3 x sin (25) Sin-1 θ2 = .42/3 =.14 θ2 = 8° 10. Draw a diagram for the situation described in question nine. ׀ ׀ ׀ 11. What kinds of waves obey the law of reflection? All waves. 12. How far does an image in a plane mirror appear to be behind the surface of the mirror? The same distance the object is in front of the plane mirror. 13. Is light refracted when passing between substances that have the same refractive index? No. Refer to Snell’s Law. 14. Do different colors of light have the same speed in a vacuum? Yes. 15. Do different colors of light have the same speed in substances? No, the different colors are slowed down and bent at different rates when traveling through substances . 16. Why do different colors of light become separated when going through a prism? Colors separate when going through a prism because in a prism the boundary surfaces are not parallel but rather at angles to each other causing light rays to be bent more acutely.