I. C O N T E N T S T A N D A R D S

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1 Introductory Physics, High School Learning Standards for a Full First-Year Course I. C O N T E N T S T A N D A R D S 4. Waves Central Concept: Waves carry energy from place to place without the transfer of matter. 4.1 Describe the measurable properties of waves (velocity, frequency, wavelength, amplitude, period) and explain the relationships among them. Recognize examples of simple harmonic motion. 4.2 Distinguish between mechanical and electromagnetic waves. 4.3 Distinguish between the two types of mechanical waves, transverse and longitudinal. 4.4 Describe qualitatively the basic principles of reflection and refraction of waves. 4.5 Recognize that mechanical waves generally move faster through a solid than through a liquid and faster through a liquid than through a gas. 4.6 Describe the apparent change in frequency of waves due to the motion of a source or a receiver (the Doppler effect). Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 6.1 Recognize that electromagnetic waves are transverse waves and travel at the speed of light through a vacuum. 6.2 Describe the electromagnetic spectrum in terms of frequency and wavelength, and identify the locations of radio waves, microwaves, infrared radiation, visible light (red, orange, yellow, green, blue, indigo, and violet), ultraviolet rays, x-rays, and gamma rays on the spectrum.

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3 4. Waves Central Concept: Waves carry energy from place to place without the transfer of matter. 1. Which of the following is the best example 2. The diagram below shows a wave trace. of a wave? A. a stone rolling downhill B. a vehicle traveling on a bumpy road C. a string vibrating on a guitar D. a grasshopper jumping up and down occasionally. C. A vibrating guitar string is a wiggle in space and time that repeats regularly. The matter in the guitar string does not move from one placed to the other, but the energy does. Distance Z is a measure of A. amplitude. B. frequency. C. wavelength. D. wave speed. A. The amplitude of a wave is the distance from the midpoint to the highest point of the wave crest or the lowest point of the wave trough.

4 4. Waves Central Concept: Waves carry energy from place to place without the transfer of matter. 3. The illustration below shows three toy ducks floating on water, moving up and down as a wave travels to the right with a velocity of 3 m/s. 4. The figure below shows a spring with a wave traveling through it. Which of the following is the frequency of the wave? A Hz B Hz C. 1.5 Hz D. 6.0 Hz Which type of wave is illustrated? A. sound B. transverse C. longitudinal D. electromagnetic A. Wave speed = wavelength x frequency. Frequency = Wave speed / Wavelength Frequency = 3m / s 4m.75Hz C. In longitudinal waves, the wave pulse is in the same direction that the wave is traveling. As the wave travels, the medium undergoes compressions and rarefactions.

5 4. Waves Central Concept: Waves carry energy from place to place without the transfer of matter. 5. What is the frequency of ocean waves that have a speed of 18 m/s and a wavelength of 50 m? A Hz B Hz C. 2.8 Hz D. 9.0 Hz 6. The diagram below represents a mass suspended vertically by a rubber band. The mass is set in motion by pulling down slightly on the mass and letting go. Which of the following correctly identifies the up-and-down motion of the mass? A. torsional B. transverse C. nonharmonic D. simple harmonic B. Wave speed = wavelength x frequency. Frequency = Wave speed / Wavelength 18m /s 50m.36Hz D. The up and down oscillation of a spring or the back and forth motion of a pendulum is called simple harmonic motion.

6 4. Waves Central Concept: Waves carry energy from place to place without the transfer of matter. 7. An organ pipe produces a musical note with 8. Which of the following best describes the a wavelength of 2.72 m. What is the frequency relationship between frequency and of this note if the speed of sound is 348 m/s? wavelength of electromagnetic waves? A Hz A. If the frequency remains constant, the B. 128 Hz wavelength increases. C. 260 Hz B. The wavelength decreases as the frequency D. 466 Hz decreases. C. The frequency increases as the wavelength decreases. D. If the wavelength remains constant, the frequency increases. B. Wave speed = wavelength x frequency. Frequency = Wave speed / Wavelength 348m /s 2.72m 128Hz C. As wavelengths become shorter, more of them will occur in a given amount of time. Mathematically: v = f Since the wave speed for all electromagnetic waves is the same. If the wavelength gets bigger, the frequency must go down to keep their product constant.

7 4. Waves Central Concept: Waves carry energy from place to place without the transfer of matter. 9. Five bowling balls are lined up touching one 10. What causes sound? another on a smooth surface. Striking the first A. sunlight ball with a hammer makes the fifth ball move B. vibrations away from the group. The force of the hammer C. x-rays was transmitted through the line of balls as D. pitch what type of wave? A. electromagnetic B. heat C. longitudinal D. transverse C. The wave energy is traveling parallel to the direction of the pulse. B. All sounds are caused by the vibrations of material objects. Note that sunlight and X-rays are examples of electromagnetic waves, NOT sound waves. Pitch is a property of sound, but it is not the cause of sound.

8 Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 11. Sound reaches our ears because sound makes air particles A. heat up. B. cool down. C. slow down. D. vibrate. 12. What property of electromagnetic waves makes it possible to use these waves to transmit information between a space shuttle and NASA mission control centers on the ground? A. Electromagnetic waves are transverse waves. B. Electromagnetic waves have very low velocity. C. Electromagnetic waves are all visible to human eyes. D. Electromagnetic waves can travel through a vacuum. D. The vibration of air particles causes the vibration of the parts of our ears which send a signal to our brain which we perceive as sound. D. Electromagnetic waves do not require a medium to travel from one place or another. The waves themselves consist of electric and magnetic fields, and do not depend on the vibration of particles of matter. Note that answer A is true, but doesn t explain why they are used. Answers B and C are false.

9 4. Waves Central Concept: Waves carry energy from place to place without the transfer of matter. 13.) Each of the following illustrations shows the movement of a 1 kg object. Which of these is an example of simple harmonic motion? B. Simple harmonic motion is an oscillation, a repeated back and forth movement. Correct Answer and Explanation

10 Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 14. The chart below shows a portion of the electromagnetic spectrum. A plastic filter is fitted over a light. The light emits white light, but the filter only lets the longest wavelengths of visible light pass through. Which color would a person looking at the filtered light see? A. green B. red C. violet D. yellow 15. Which of the following is designed to transform an electromagnetic wave into a mechanical wave? A. a portable radio B. a television screen C. a computer monitor D. a mercury thermometer B. Red light waves are the longest of the visible spectrum, followed by orange, yellow, green, blue, and violet. Violet waves are the shortest of the visible spectrum. A. Radio signals are carried on electromagnetic radio waves. In a radio, that wave energy is transferred to the vibration of a speaker, which sets up mechanical waves (sound waves, to be specific) through the air. Television screens and computer monitors produce electromagnetic waves (visible light). Thermometers do not really use either type of wave.

11 Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 16. The figure below shows the regions of the electromagnetic spectrum. Which of the following statements best compares the wavelengths of the regions of the electromagnetic spectrum? A. Microwaves are shorter than x-rays. B. Infrared waves are longer than gamma rays. C. Radio waves are shorter than visible light waves. D. Ultraviolet waves are longer than visible light waves. B. As it is drawn here, the longest wavelengths are on the left of the spectrum, and the shortest are on the right,. Infrared waves are much longer than gamma waves, which are the shortest on the spectrum.

12 Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 17. Which of the following devices relies on electromagnetic radiation in the radio wave region of the spectrum for operation? A. sun tanning lamp B. electric light bulb C. cellular telephone D. electric toaster 18. Which of the following colors of visible light has the longest wavelength? A. red B. blue C. green D. orange C. Cellular telephone signals are transmitted at frequencies in the radio (and microwave) portion of the electromagnetic spectrum. Tanning lamps produce mostly UV and some visible radiation. Light bulbs produce mostly visible and some IR radiation. Toasters produce mostly IR and some visible radiation. A. Red light waves are the longest of the visible spectrum, followed by orange, yellow, green, blue, and violet. Violet waves are the shortest of the visible spectrum.

13 Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 19. Visible light passes through glass. Other types of electromagnetic radiation are able to pass through other materials in a similar way. Which of the following are used in medical technology because they can pass through some parts of the human body? A. x-rays B. infrared waves C. microwaves D. ultraviolet rays 20. Some campers are sitting around a campfire outside their tent. Which product of the fire is in the form of electromagnetic waves? A. light B. smoke C. sound D. water vapor A. X-rays can penetrate the soft tissues of the human body, but cannot travel through teeth and bones. A. Visible light is a form of electromagnetic waves. Smoke and water vapor are not waves at all, and sound is a mechanical wave.

14 Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 21. Which of the following describes how a microwave oven heats food? A. The oven s interior reflects heat onto the food. B. The oven s interior, like a lens, focuses heat onto the food. C. Water molecules in the food reflect energy from microwave radiation. D. Water molecules in the food absorb the energy of microwave radiation. 22. The figure below shows regions of the electromagnetic spectrum. Which of the following waves has the highest frequency? A. visible light B. microwaves C. ultraviolet rays D. infrared radiation D. The wave frequency generated by microwave ovens causes water molecules to absorb energy and vibrate. This increase in kinetic energy of the water molecules is an increase in temperature. The heat from the water molecules can then be transferred (by conduction) to other kinds of molecules in the food. C. Ultraviolet rays have higher frequencies than visible light. Visible light has a higher frequency than infrared, and infrared has a higher frequency than microwaves.

15 Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 23. A sound wave can be transmitted through all of the following except A. a gas. B. a liquid. C. a solid. D. a vacuum. 24. Which of the following statements applies to a longitudinal wave? A. The motion of the medium is random. B. The motion of the medium is in a circular pattern. C. The motion of the medium is parallel to the motion of the wave. D. The motion of the medium is perpendicular to the motion of the wave. Answer: D. a vacuum. Sound is a mechanical wave, it requires a medium to be transmitted. Answer: C. A longitudinal wave is defined as a wave in which the motion of the medium is parallel to the motion of the wave.

16 Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 25. A student standing on the edge of a swimming pool sees a painted mark on the bottom of the pool. The mark appears to be at a shallower depth than the actual depth of the pool. Which of the following descriptions of light waves best explains this observation? A. Light from the mark travels through the water in a curved path. B. Light from the mark is refracted as it travels from the water to the air. C. Light from the mark is reflected as it travels from the water to the air. D. Light from the mark bounces off the boundary between the water and the air. 26. A student is sitting in a large stadium far away from the starting line of a footrace, while listening to the footrace on the radio. As the race starts, the student hears the sound of the starting pistol on the radio. Shortly after that, the student hears the sound of the starting pistol from inside the stadium. Which of the following best explains these observations? A. Mechanical waves travel faster than electromagnetic waves. B. Electromagnetic waves travel faster than mechanical waves. C. The radio's signal traveled a shorter distance than the sound wave traveled. D. The radio s microphone was farther away from the starting line than the student was. Answer: B. Light crossing a boundary between two media will change its direction (if the speed of light is different in the two media). This property is called refraction. Answer: B. The sound of the starting pistol travels as an electromagnetic wave from the microphone to the radio speaker, and as a mechanical wave from the source to your ear. Electromagnetic waves travel at the speed of light through a vacuum, always faster than mechanical waves.

17 Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 27. People perceive sound differently in air than they do under water. Which of the following correctly compares the motion of sound waves in air and in water? A. Sound waves travel faster in air than in water. B. Sound waves travel slower in air than in water. C. Sound waves travel in air but do not travel in water. D. Sound waves travel at the same speed in air and in water. Answer: B. Air molecules are further apart than water molecules. The wave will propagate faster through a denser The diagram below shows what happens when a particular light wave strikes a boundary.

18 Practice: Open-response question #1 The electromagnetic spectrum is shown below. There are multiple stages involved in the transmission, reception, and display of a television broadcast. A signal is sent by satellite from the station and relayed to the television by several methods. The signal is translated electronically and converted into an image on regular, liquid crystal, or plasma TV displays. The viewer then sees the image. a. Identify one region of the electromagnetic spectrum used by television and explain how it is used. The radio section of the electromagnetic spectrum is used in television broadcasts. The transmitter at the TV station sends out a signal as a series of radio waves that carry the information to individual TV s. OR The visible section of the electromagnetic spectrum is used by televisions. The television produces a visible image that consists of different wavelengths of visible light. Different wavelengths are visible as different colors. b. Select a different portion of the electromagnetic spectrum that is not used by television. Explain a useful application of this spectral region. Microwaves are not used by TV. One useful application of microwaves is the microwave oven, which shines microwaves on food. The water molecules in the food absorb the microwaves and heat up. OR Infrared waves are not (really) used by TV. (It is true that most TV s get hot, so they will emit IR radiation to their surroundings. However, this is not really using IR waves). A useful application of IR waves is in heat lamps. Heat lamps emit IR radiation that can be absorbed by food placed under them. This keeps the food warm. IR waves are also often used in remote controls. The remote control produces a signal that is transmitted to the television (or other device) via IR waves. OR Ultraviolet waves are not used by television. UV rays can be used to sterilize (kill bacteria on) things. Often, you will find UV rays in restaurant kitchens for employees to sterilize their hands. Some labs will have cabinets where UV rays sterilize safety goggles. Biology labs use UV lights to sterilize surfaces and prevent contamination of cells and organisms grown in the lab. OR X-rays are not used by television. X-rays can be used for medical purposes. Since they pass through soft tissues of the human body but not through bones, X-rays can be used to produce images of the bones and teeth. OR Gamma rays are not used by television. Gamma rays can be used in the treatment of cancer. The gamma rays can be aimed at a tumor, killing the cancerous cells.

19 Practice: Open-response question #2 BE SURE TO ANSWER AND LABEL ALL PARTS OF THE QUESTION. Show all your work (diagrams, tables, or computations) If you do the work in your head, explain in writing how you did the work. What happens when light wave strikes a boundary? QuickTime and a decompressor are needed to see this picture. a. Identify each light ray, A, B, and C, as an incident, a refracted, or a reflected ray. b. Describe the relationship between angles x1 and x2. c. Describe how this setup could be changed so that the size of angle x3 is different. Answer A. Ray A is the incident ray, B is the reflected ray, and C is the refracting ray. B. Angles x 1 and x 2 are equal. The angle of incidence is equal to the angle of reflection. C. The angle x 3 depends on what materials are on the two sides of the boundary. In the picture, x 3 is smaller than x 1, which indicates that the light moves faster in Medium 2 than it does in Medium 1. To change the angle, you could change either medium in which light travels with a different speed.