Sound and Light

Sound and Light PowerPoint PPT Presentation


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Baski - Summer 2003. PHYS 510 Notes: Sound

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Sound and Light

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1. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Sound and Light Waves = periodic motion with amplitude & frequency Types = transverse (light) & longitudinal (sound) Sound = longitudinal pressure wave Production using a speaker, decibel loudness Light = transverse electromagnetic wave Reflection with planar/convex/concave mirrors Refraction with convex/concave lenses Eye and Eyeglasses Dispersion in Prisms/Rainbows

2. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Waves: Activity to Observe Two Wave Types There are two major types of waves: transverse (light) and longitudinal (sound). For a wave traveling horizontally, notice how the slinky coils move up/down for transverse waves and left/right for longitudinal waves.

3. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Waves: Transverse and Longitudinal

4. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Waves: Transverse and Longitudinal

5. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Waves: Amplitude and Frequency The amplitude A of a wave is the height of the wave from peak to peak (or trough). It is directly related to the volume of a sound wave. The frequency f of a wave is the inverse of its period T, which is the repeat time from peak to peak. A higher frequency sound wave has peaks that are closer together in time and has a higher pitch. How do the amplitude and frequency of the wave drawn above change with time?

6. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Sound: Sound vs. Light Sound and light both travel as waves, but they are VERY DIFFERENT phenomena. Sound is a longitudinal pressure wave, and light is a transverse electromagnetic wave. Why do we see lightning before hearing thunder?

7. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Sound: Longitudinal Waves Sound produces a periodic pressure variation in the air, where air molecules vibrate back and forth. Can you hear anything in outerspace (or in a vacuum)?

8. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Sound: Activity to Build a Speaker A loudspeaker converts an electrical signal into a sound signal. It uses an electromagnet (attached to a speaker cone) to convert a changing electrical current into a changing magnetic field. The electromagnet then interacts with a permanent magnet in the speaker, which causes the electromagnet (and speaker cone) to move back and forth. The motion of the speaker cone then creates sound pressure waves.

9. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Sound: Volume The amplitude of a sound wave is related to its volume or loudness. Due to the very large range of volumes heard by our ear, the decibel scale for sound volume is NOT linear, but logarithmic (by 10’s). An increase of 10 dB (decibels) is equal to a sound that is 10 times louder. An increase of 20 dB is equal to a sound that is how many times louder?

10. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Light Waves = Electromagnetic Waves Visible light is an electromagnetic wave with perpendicular electric and magnetic fields. Visible light has a wavelength l of 450 to 750 nanometers (nm) (A piece of paper is ~0.1 millimeters or 100,000 nanometers thick.) Waves with shorter or longer wavelengths are not visible to our eyes!

11. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Electromagnetic (EM) Spectrum Visible light is only a small portion of the electromagnetic spectrum, which ranges from low frequency/energy radio waves to high frequency/energy gamma rays. The velocity of all electromagnetic radiation is 300,000 km/s in air. It travels around the earth 7.5 times in only one second! Velocity decreases in materials denser than air (slower in glass).

12. Baski - Summer 2003 PHYS 510 Notes: Sound & Light EM Spectrum: Solar Radiation The sun produces EM radiation of all frequencies, where radio waves and visible light easily reach us. X-rays from outerspace are fortunately stopped by our atmosphere. Some UV rays DO ENTER our atmosphere and DAMAGE our bodies.

13. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Reflection: Planar Mirror When light reflects from a planar (flat) mirror, the incoming incident angle and outgoing reflection angle are equal. Note: Angles are always measured with respect to the perpendicular (or normal) to the mirror plane.

14. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Reflection: Planar Mirror A “virtual image” of an object always appears in a planar mirror. A virtual image appears normal to us, but NO LIGHT actually exists where the image is supposed to be!

15. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Reflection: Activity to Construct a Periscope The periscope uses two mirrors so that you can observe an object above your line of sight. Can you locate the mirrors above and draw the light path?

16. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Reflection: Activity to Construct a Kaleidoscope

17. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Reflection: Convex Mirror (Activity with Spoon) A convex mirror is bent outwards and “distorts” the image. The reflection always appears upright (virtual image) and is smaller.

18. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Reflection: Convex Mirror Application Because images always appear smaller in a convex mirror, a larger “field of view” is possible. Such mirrors are used for car side-view mirrors and surveillance mirrors in stores. Do you understand why car mirrors have the warning given in the cartoon?

19. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Reflection: Concave Mirror (Outside Focus) A concave mirror is bent inwards and also “distorts” the image. When an object is outside the focus of a concave mirror, the reflection appears upside-down (real image).

20. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Reflection: Concave Mirror (Inside Focus) When an object is inside the focus of a concave mirror, the reflection appears upright (virtual image).

21. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Refraction: Air/Glass Boundary Light “bends” or refracts between different types of material (due to slower velocity in denser materials). It is bent closer to the perpendicular in denser materials (water, glass). Can you draw the path of a light ray from air through a piece of glass?

22. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Refraction: “Tricks” on our Eyes Due to refraction of light from the water to the air, the fish appears closer to the surface than it actually is! Have you seen this phenomenon before? Where?

23. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Lenses: Convex and Concave Lenses A convex glass lens (converging) uses refraction to bend light inwards, whereas a concave lens (diverging) bends light outwards. For a convex lens, parallel light rays can be bent to a focal point.

24. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Lenses: Activity with a Light Box What happens when a convex and concave lens are combined?

25. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Lenses: Eye Your eye uses a convex lens to focus light images onto the retina. Notice that the retinal image is inverted!! Your brain processes this information so that objects “appear” upright to you.

26. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Lenses: Eyeglasses for Near- and Farsightedness

27. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Dispersion: “Spreading” of Visible Light When light is refracted, blue light bends more than red. Refraction therefore causes light to “spread” or disperse into its component colors, just as you see for sunlight hitting a prism.

28. Baski - Summer 2003 PHYS 510 Notes: Sound & Light Dispersion: Rainbow Refraction also causes rainbows to form, where the sun’s light is refracted inside raindrops and spreads to form the rainbow colors: red, orange, yellow, green, blue, indigo, violet.

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