HOMEWORK ANSWERS INTRODUCTORY VIDEOS

Transcription

1 DEVIL PHYSICS HOMEWORK ANSWERS Tsokos, Lesson 4.1, SL: 1-10, 12-18, 20-21, HL: 1-30 all INTRODUCTORY VIDEOS Standing versus Traveling waves: ure=related Making Standing Waves Traveling Waves Explained: ture=related Waves Explained Lesson 4.2: Traveling Wave Characteristics

2 1. Objectives. By the end of this class you should be able to: a) state what is meant by wave motion b) distinguish between longitudinal and transverse waves c) define amplitude, wavelength, period, and frequency and state the relationship between them, d) state what is meant by crest and trough and identify these on a graph e) find amplitude and period from a displacementtime graph f) find amplitude and wavelength from a displacement-position graph g) understand the meaning of the terms wavefront and ray h) use 2. What is a wave? a) A wave is a way of transferring energy and momentum from one place to another, but without the actual large-scale motion of a material body

3 b) Examples: i) Life is a beach ii) Light from the sun iii) Soprano breaking a glass iv) Light travels in a vacuum no medium required an electromagnetic wave v) Sound and water require a medium mechanical waves c) Waves occur because something is disturbed d) A wave is a disturbance that travels, transferring energy and momentum from one place to another, but without the actual large-scale motion of a material body. The direction of energy transfer is the direction of propagation of the wave. 3. Transverse and Longitudinal Waves longitudinal and transverse waves a) Transverse waves in which the disturbance is at right angles to the direction of energy transfer i) rope tricks ii) electromagnetic waves

4 b) Longitudinal -- waves in which the disturbance is along the direction of energy transfer i) dominos ii) sound waves

5 c) energy propagated through a series of compressions (region of higher than normal density) and rarefactions (region of lower than normal density)

6 4. Wave pulses a) rope tricks i) half-pulse vs. full pulse

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8 ii) wave pulses travel with a given speed determined by the tension in the rope and mass per unit length, μ = m/l iii) the speed of the wave is determined by the properties of the medium and not by how the wave is created, iv) i.e. independent of shape or how fast you produced it 5. Travelling waves a) those that take more than one step before dribbling (N/A NBA) b) when pulses are repetitiously produced c) if the wave driver demonstrates SHM, the wave produced will exhibit SHM and the wave will look like a sine wave (also called a harmonic wave) 6. Harmonic waves a) exhibit SHM

9 b) period (s) time to complete one full wave, unit is s c) wavelength ( ) length of a wave (surprise!) d) velocity (v) equal to one wavelength (m) per the period (s) e) frequency ( ) number of waves per unit time, equal to 1/T, unit is s -1 or Hz,, The marvels of Algebra!!! f) displacement (y) height obtained above or below the undisturbed point due to the

10 disturbance, it is a function of the distance (x) and time (t) i) When wave movement is dependent on the medium, displacement is given in terms of density: or in terms of pressure g) displacement is a function of distance and time for any wave h) graphs of displacement versus position let us determine wavelength, i) graphs of displacement versus time let us determine period, T j) Points on the wave with maximum displacement are call crests and those at the minimum displacement are called troughs k) In a travelling wave, the crests will steadily move forward until the period is reached which is where the wave will look like it originally did when it was disturbed

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12 7. Example Questions: a) A radio station emits at a frequency of 90.8 MHz. What is the wavelength of the waves emitted? Since they are electromagnetic waves, they travel at the speed of light, 3x10 8 m/s f = 90.8x10 6 s -1 b) A sound wave of frequency 450Hz is emitted from A and travels towards B, a distance of 150m away. Take the speed of sound to be 341 m s -1. How many wavelengths fit in the distance from A to B? f = 450 s -1 v = 341 m s -1,

13 c) The noise of thunder is heard 3 s after the flash of lightning. How far away is the place where the lightning struck? (Use 340 m s -1 for the speed of sound) Since light travels so fast, you can assume you saw it instantaneously. v x t = d (340 m s -1 )(3 s) = 1020 m 8. Wavefronts and Rays a) If you consider a wave to be moving horizontally, a wavefront is a plane perpendicular to the wave and perpendicular to the direction the wave is travelling b) Rays are a pretty good baseball team c) They are also mathematical lines perpendicular to the wavefronts in the direction the wave is travelling d) Examples: i) The waves on the beach would have a rectangular wavefront ii) If you drop a stone in the water, the wavefront would be cylindrical iii) Light waves from a point source would have spherical wavefronts

14 Period 5 -- STOPPED HERE Period 6 -- STOPPED HERE Summary 1. Objectives. Are you able to: e) state what is meant by wave motion f) distinguish between longitudinal and transverse waves g) define amplitude, wavelength, period, and frequency and state the relationship between them, h) state what is meant by crest and trough and identify these on a graph i) find amplitude and period from a displacementtime graph j) find amplitude and wavelength from a displacement-position graph k) understand the meaning of the terms wavefront and ray l) use Look Ahead Video

15 ture=related Oscillating Vortex Flows Lesson 4.2: Homework SL: Assignment #1, 1-10 HL: Assignment #1, 1-10 Optional Reading Giancoli, Chapter 11, Sections 1-6 University Physics, Chapter 13 Holt Physics, Chapter 11