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Published byDanielle Hughes Modified over 2 years ago

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Welcome Here!!! Begin by turning in Fridays lab (if you didnt already on Friday). Then remind someone around you of the similarities and differences between reflection, refraction, and diffraction.

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Todays Agenda: Discuss Fridays lab Lesson: Waves on Strings In-class practice questions HW: Waves on Strings Worksheet (due Wed, graded for correctness)

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Learning Goal: Students will be able to predict which frequencies will resonate to produce standing waves on a given string.

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Intro: If a string is connected at one end to a stationary clamp, and then the free end is vibrated up and down, waves begin to travel down the string, and reflect and ________ from the fixed end. With waves traveling in both directions, ____________ interference will happen. If the string is vibrated at just the right frequency, the wave will appear to stand still, so its called a ___________ wave. invert destructive standing

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Standing Waves:

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The parts of the wave where complete destructive interference continually occurs are called ________, and the parts of the wave with maximum displacement are called ___________. nodes antinodes

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Waves on Strings: When a string is plucked, only certain frequencies will resonate, and these frequencies are based on the _______ of the string. The lowest frequency to resonate is called the fundamental freq. ( f 1 ) The other resonant frequencies are called harmonics or overtones. length

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Waves on Strings: f 1 = v/ 1 = v/2L f 2 =v/L =2f 1 f 3 = v/(2/3)L =3f 1 v/ 2 = v/ 3 =

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Example Problem: Waves travel on a 2.4m-long string at a speed of 150m/s. What are the lowest 3 frequencies that will cause this string to resonate to produce standing waves?

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Group Practice Problems: 1. The string in the picture is vibrating at 330Hz. What is the fundamental frequency of this string? 2.The velocity of waves on a certain 32cm-long spring is 120m/s. Find the fundamental freq. and the 2 nd and 3 rd harmonics of this spring. 3.The string in the picture is vibrating at 1200Hz. If waves travel on this string at 60m/s, how long is the string?

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Group Practice Problem Answers: 1.110Hz 2.f 1 = 187.5Hz f 2 = 275Hz f 3 = 562.5Hz m

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