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## Chapter 5 Let Us Entertain You.

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**Chapter 5Let Us Entertain You.**Sound and Light**How do stringed instruments make notes?**• Guitar • Ukelele**How do stringed instruments make notes?**• Koto • Violin**How do stringed instruments make notes?**• Piano • Harp**A word about pitch:**High note = High pitch = High frequency Low note = Low pitch = Low frequency**A vibrating string:**• What affects the frequency of vibration?**Frequency is……**• ______________related to the ___________ of the tension on the string • ______________related to the ___________ of the length of the string • ______________related to the ___________ of the mass of the string**Frequency is……**• ____Directly___ related to the _square root_ of the tension on the string • ___Inversely___ related to the _square root_ of the length of the string • ___Inversely___related to the _square root_ of the mass of the string**Frequency is….**f= T 4mL**Waves:**• Carry energy (Greater amplitudemore energy) • Have a velocity, wavelength, frequency and amplitude (Frequency and wavelength are inversely related) • Velocity depends on the medium • Interfere (add up) • Can be transverse (↕) or longitudinal (↔)**The wave equation:**Velocity = frequency x wavelength v = f l (m/s) = (/s) x (m) (frequency and wavelength are inversely related)**Calculate:**• Waves on water have a wavelength of 2.0 m, and a frequency of 3 Hz (3 waves / second). What is their speed? • A vibrating guitar string has a frequency of 512 Hz, carrying a wave that moves at 320 m/s. What is its wavelength? • What is the frequency of a radio wave that travels at 3.00 x 10 8 m/s and has a wavelength of 3.134 m?**Wave motion **• Wave motion **Motion of medium**• Motion of medium**Woodwinds.**• The resonance of sound in an open tube: • Please notice the antinodes at the open ends.**Woodwinds.**• What is the length of the entire wave?**Woodwinds.**• What is the length of the entire wave? • The tube holds half a wave, so l=2L**If one end is closed:**• There is a node at the closed end, and an antinode at the open end.**If one end is closed:**• There is a node at the closed end, and an antinode at the open end. • What is the length of the wave?**If one end is closed:**• There is a node at the closed end, and an antinode at the open end. • One-fourth of the wave fits into the tube, so l=4L.**HW p 526**• 1) (Pretty good) • Similar: vibrations make sound, frequency and wavelengths • Different: String vibrating makes air vibrate vs air itself vibrates**HW p 526**• 2) a. Did you draw them (3 or 4) full-sized? • b.**HW p 526**• 2) b. (cont’d) • c) longest wavelenths=lowest frequencies**HW p 526**• answers vary (2.4 m normally—19.5 m record) b. c. L of pipe= ¼ wavelength • (wavelength=4 x L of pipe) • d freq and wavelength are inversely related.**HW p 526**4) L of pipe= ¼ wavelength • (wavelength=4 x L of pipe) • f=v/l • Which is higher? How much higher freq.? f=v/l, freqand wavelength are inversely related. 6) t=d/v**Apply the wave equation:**• A wave has a frequency of 58 Hz and a speed of 31 m/s. What is the wavelength of this wave? • A periodic transverse wave is established on a string such that there are exactly two cycles on a 3.0-m section of the string. The crests move at 20 m/s. What is the frequency of the wave? • A 4-m long string, clamped at both ends, vibrates at 200 Hz. If the string resonates in six segments, what is the speed of transverse waves on the string? • Four standing wave segments, or loops, are observed on a string fixed at both ends as it vibrates at a frequency of 140 Hz. What is the fundamental frequency of the string? • Vibrations with frequency 600 Hz are established on a 1.33-m length of string that is clamped at both ends. The speed of waves on the string is 400 m/s. How many waves are on the string?**Light**• Light is a transverse wave (an electromagnetic wave) • Light travels in a straight line**Light**• A shadow falls where light is blocked • No shadow • Shadow • No shadow**Light**• A shadow falls where light is blocked…BUT! • No shadow • Shadow • No shadow**Light**• A shadow falls where light is blocked…BUT…a real light source is not a single point.**Light**• A shadow falls where light is blocked…BUT…a real light source is not a single point. • Shadow from the right side of the bulb**Light**• A shadow falls where light is blocked…BUT…a real light source is not a single point. • Shadow from the left side of the bulb**Light**• A shadow falls where light is blocked…BUT…a real light source is not a single point. • Overlapping shadows (umbra)**Light**• A shadow falls where light is blocked…BUT…a real light source is not a single point. • Non-overlapping shadow (penumbra) • Non-overlapping shadow (penumbra)**Light**• A shadow falls where light is blocked…BUT…a real light source is not a single point. • Light from both sides (no shadow) • Light from both sides (no shadow)**di**do**di**do**di=doThe image is directly behind the mirror at the same**distance the object is in front of the mirror di do