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Lecture 21

PHY 2020 Lecture 21: Chapter 21-22

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PHY 2020

Chapter 21-Musical Sounds - Noise corresponds to an irregular vibration of the eardrum. - Can a car engine really sing? o Yes, French car playing British anthem - Musical sounds o Three characteristics ▪ Pitch ▪ Intensity ▪ Quality - Pitch has to do with frequency o Slow vibrations (low frequency)-> long period (low pitch) - Figure 21.2. o A piano keyboard covers a little more than seven octaves o Multiply the frequency on any note by 2, and you have the same note a higher pitch. - Changing vibrating sound source o Alternating the size o The tightness o Mass of the vibrating object. - Sound Intensity and Loudness. o Intensity depends on amplitude of pressure variations ▪ Intensities of ear covering range from 10^-12 w/m^2 (threshold of hearing) to move than 1 w/m^2 (threshold of pain) ▪ 10^-12 w/m^2 as a reference intensity called 0 bel or 0 decibel - Intensity- physical attribute of a sound wave - Loudness- sensation of intensity - Ear infection throws off balance because o The fluid in semilunar canal is not equal to other ear. - Cochlea sends signals to brain Quality - Quality, the “color” of a tone- timbre o Timbre describes all of the aspects of a musical sound other than pitch, loudness, or length of tone. - Figure 21.5: Modes of vibration of guitar string o Partial tones: a single-frequency component sound wave of a complex one. When the frequency of a partial tone is an integer multiple of the lowest frequency, it is referred to as a harmonic. o Fundamental frequency: The lowest frequency of vibration, or first harmonic, in a musical tone. #73. A guitar and a flute are in tune with each other. Discuss how a change in temperature could alter this situation. - Temperature affects the strings tightness and sound. #38. If sound becomes louder, which wave characteristic is likely increasing: Frequency, wavelength, amplitude, or speed? - Loudness goes with amplitude and frequency #39. Explain how you can lower the pitch of a note on a guitar by altering the string’s (a) length, (b) tension, or (c) thickness or mass. - A lower pitch is produced when a guitar strong is (a) lengthened, (b) loosened so that the tension is reduced, and (c) made more massive, usually by windings of wire around the string. That’s why bass strings are thick-greater inertia. #40. Does the pitch of a note depend on sound frequency, loudness, quality, or all of these? - Pitch depends on frequency. Clicker and Homework Questions 1. The source of all musical sound is something Vibrating 2. Low-pitched sounds have Both f these; low frequencies and long periods 3. The frequency of a note one octave higher in pitch than a 440-hertz note is 880 Hz 4. Joseph Fourier discovered that periodic waves can be represented by Sum of a series of simple sine waves 5. Our ears sort out the complex jumble of sounds that reach them. In so doing, our ears perform a sort of Fourier analysis 6. Musical sounds from CD or DVD relies on All of these 7. What is the threshold of hearing? None of the above (0 decibel) 8. The pitch of musical sound depends on the sound wave’s Frequency 9. The fundamental frequency of a violin strong is 440 hertz. The frequency of its second harmonic is 880 hertz. 10. As we become older, the frequency range of human hearing Decreases 11. The loudness of a sound is most closely related to its Intensity. Chapter 22- Electrostatics - Figure 22.1: Like charges repel. Unlike charges attract. - Benjamin Franklin in charge of name (positive and negative) - Figure 22.2: Model of helium atom. The atomic nucleus is composed of two protons and two neutrons. The positively charged protons attract two negative electrons. - Figure 22.3: Electrons are transferred from the fur to the rod. The rod is then negatively charged. Is the fur charged? How much compared to the rod? Positively or negatively? o Yes the fur is charged. Compared to the rod it has the same charge. The charge of the rod is positive (unlike charges attract) - Charges in a conserved quantity. - What is the unit of charge? o Coulomb - What does it mean when we say that charge is: o Quantized ▪ Comes in tiny discreet packages o Conserved
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