Physics 222 Study Guide

Transcription

1 Unit 2: Waves & Unit 3: Light Use this course guide to help you prepare for Exam 2. This Guide is designed to give an overview of the main concepts, equations, and vocabulary that will be tested in Unit 1. The questions asked below are NOT the questions that will be on Exam 1, but are to be used to help you study for the examination. Using this study guide is not required, but can be helpful. Effective Preparation for Exams: - The following steps are recommended to help you prepare for each exam: - Do not wait for the last minute to study for the exam! - Setup a chapter of HW problems and study at least an hour each day. - Keep a record of all the equations you use, and notice which are used most often. - Check the Formula Sheet for the Final Exam (on the webpage), to be aware of which equations you use are most important. - Redo Clicker Questions, lecture problems, worked out problems in the text, and any practice quizzes. - Reread the lecture notes. - Make use of the animations used in lecture - found via links on the course webpage, to help you understand the material. - Ask questions during office hours Tips: Don t spend more than 15 minutes on a problem, move on to the next one! Later return to problems you were stuck on and you might no longer be! Physics takes A LOT of practice. Work at it each day. Don t cram! Form a study group with a few students. Make use of office hours, MESA, TLC, study buddies,... Physics is not about learning facts. It is about thinking and reasoning, using logic to explain relationships between facts and the patterns in nature. When studying look for the logic underlying all examples and problems. Reason like a physicist. You will get more out of the lectures if you read through the material BEFORE coming to class Do NOT copy other peoples homework. Do NOT be a lab parasite who always copies other people s work Have a POSITIVE attitude and relax! Don t Stress!

2 Waves What is a wave? What moves in a wave? How does a wave differ from an oscillation? What characteristic or property must the medium have through which the wave travels? What motion does the disturbance have to have to be a source of a sinusoidal wave? In your own words define what a transverse wave is and give an example of a transverse wave. Explain how you identify this as a transverse wave? In your own words define what a longitudinal wave is and give an example of a longitudinal wave. Explain how you identify this as a longitudinal wave? Create a problem where wavelength and amplitude are measured, the period is observed, and then calculate wave speed and wave frequency. Draw both y versus x and y versus t graphs for this wave.

3 Describe what happens to a wave when it enters a more/less dense medium. How does tension relate to a wave on a string? What wave parameters change when tension is varied? What does each symbol mean in the sinusoidal displacement equation for a wave? Draw history and snapshot graphs for a few waves with differing parameters If a wave has a speed -v, with a period T (make up values and solve for λ and f) plot a history and snapshot graph for location x and location x = λ/4 at t = 0 and t = T/4.

4 What is total phase and the phase constant? Draw graphs of waves with differing phase constants. What is the range of visible light in nm, m, μm, and Hz? What is the index of refraction and how does λmatter relate to λvacuum Sound Waves What is the relation for velocity of sound to temperature of a simple gas?

5 How does sound speed relate to density? Draw both a displacement and a pressure graph for a sound wave. pictures relate to each other and how much they are phase shifted. Explain how the What is power and intensity for sound? What minimum intensity is the threshold of hearing? What is a decibel and the sound intensity level equation? Calculate how many db corresponds to a doubling and tripling in sound. How much of an increase of db usually sounds twice as loud? What is the doppler effect and the relevant equations. Calculate two examples.

6 Wave Interference What is a standing wave? Is it a real wave? Define nodes and antinodes and how they can quantify harmonics. Illustrate with both pressure and displacement graphs sound waves standing in openopen, open-closed, and closed-closed tubes. Write the related wavelength and frequency equations to tube length next to each drawing. What is resonance? What is a beat frequency, carrier frequency, and musical chord?

7 You hear an A-note. What is a possible frequency, period, and wavelength at 20º C? If you hear the A-note from a distance r away, with an intensity of 70 db, what is the intensity I of the sound heard and power in joules from the source of sound? If the note is played from a source that is moving at you at a speed v, what is the frequency heard by the stationary observer? If the A-note is played in a tube of length L, in which there air inside is at 20º C, draw three harmonics of the A-note in an open-open, an open-closed, and a closed-closed tube and calculate the length of each of the three tubes.

8 If the same A-note from above is played identically by two identical speakers and the speakers are a distance d apart creating one-dimensional destructive interference occurs so that no sound is heard, calculate a possible distance d. Calculate two other distances of separation of the speakers in 1-d, so that a minimum sound will be heard. Calculate three other distances of separation of the speakers in 1-d, so that a maximum sound will be heard. Introduce another speaker which emits one frequency that is a different musical note where the beat frequency of the speakers is also a musical note (i.e. a chord). Determine these two new frequencies (see the image of the notes on a piano from lecture).

9 Describe how thin-film interference works. Create an example of two identical monotone sound waves in interfering in 2-d. Create values to identify wavelength, frequency, and multiple locations of constructive and destructive interference relating to angle from a midline between the sources.

10 Create a two-slit interference of light problem of a particular color. Create values to identify screen distance, frequency, and distance along screen to multiple locations of constructive and destructive interference relating to angle from a midline between the sources. What happens to the interference pattern when a color that is a shorter wavelength passes through the smae two-slits form above? What happens to the interference pattern when many more slits are used rather than two? What happens to the interference pattern when all but one slit is blocked? How does the width of the fringes relate to distance and slit-size now?

11 What is an interferometer and how does it work? involving one. Name a famous experiment What is polarization of light and how do polarizers work?

12 Light Rays What is a light ray? Can they interact or interfere with each other? How is one observed? What is specular versus diffuse reflection? What is the law of reflection? Draw with light rays how a reflection is seen in a flat mirror. What is the Principle of Least Time? How does it relate to the refraction of light? Create a quantitative example of the refraction of light using Snell s Law of Refraction and illustrate with a ray diagram.

13 Use the wavefront/tinker toy model to illustrate how light converges through a convex lens. What is chromatic aberration? Use given values to calculate the percent difference between deep blue and red in the angle of refraction, θ2, from white light in air incident at an angle θ1 on glass. Explain Total Internal Reflection, the Critical Angle, and the view from under the water looking up at the outside world.

14 Illustrate the principal (special) rays for a converging lens and mirror. Illustrate the principal (special) rays for a diverging lens and mirror. What are the advantages of mirrors versus lenses in telescopes? What are real and virtual images? What are mirages? Why do stars twinkle? How are rainbows and double rainbows formed?

15 What is the thin lens equation and magnification equations? Use principal rays in a ray diagrams to show a virtual image for each of the following a converging lens, a converging mirror, diverging lens, and a diverging mirror. Illustrate how a camera obscura and simple camera work.

16 Explain the myopic eye. What type of corrective lens is needed? Use ray diagrams to illustrate the corrected image on the retina. Explain the hyperopic eye. What type of corrective lens is needed? Use ray diagrams to illustrate the corrected image on the retina.

17 Use ray diagrams to illustrate the image in a double convex lens telescope and derive the total magnification equation. Use ray diagrams to illustrate the image in a double convex lens microscope and derive the total magnification equation.

18 Practice Quiz Waves 1. A machine tugs sideways on an elastic rope with a frequency of 5 Hz. A graph of the transverse displacements of this rope wave at t = 10.0 s as a function of position is shown. a) What is the velocity of waves on this rope? b) If the frequency of the machine tugging on the rope is doubled to f = 10 Hz, what is the new wavelength of waves on this rope? What is the new velocity of waves on this rope? 2. You are in a (very) small boat anchored in the bay. Water waves are moving by you so that a wave crest passes by every six seconds, and you notice that these crests are spaced 20 m apart. What is the velocity of these water waves? 3. The velocity of sound in air is 340 m/s at STP (standard temperature and pressure), and the velocity of sound in water is 1,500 m/s at STP. What are the wavelengths of a 3 khz sound in air and in water? 4. A wave is moving to the left with a speed of 2 m/s. If the period of this wave is 4 s, what value must the wavelength be? 5. Explain why sound cannot be heard in space. 6. The following graphs were created by two separate, swinging pendula. y (deg.) 20 º Pendulum A t (sec.) y (deg.) 20 º Pendulum B t (sec.) Which, if either, of these pendula (A or B) is longer? Clearly explain your reasoning for your answer.

19 Practice Quiz Optometry 5. Mr. Magoo is in desperate need of corrective lenses for his 3 cm long nearsighted eyeballs. He wants to see Comet Lulin and the stars tonight, but his far point is only 3 cm! What type of eyeglass lenses and strength in diopters will you prescribe for him, if his eyeglasses will be 1.5 cm from his eye? b. Will his new glasses create a real or virtual image? Explain. c. Testing his new eyewear, Mr. Magoo tries to see an object 6 cm from his eye. Will the image be visible to him? d. Use ray tracing to locate the final image for the object at 6 cm using only the principal (special) rays. Eye lens Glasses e. Is the final image real or virtual? Inverted or upright? f. Should you show Mr. Magoo his bill before or after you fit him with new glasses?