Chapter: Sound and Light

2. Table of Contents Chapter: Sound and Light Section 1: Sound Section 2: Reflection and Refraction of Light Section 3: Mirrors, Lenses, and the Eye Section 4: Light and Color

3. Sound 1 Sound • When an object vibrates, it creates sound waves. • Sound waves are compressional waves. • The compression moves away as these molecules collide with other molecules in air. • A rarefaction is formed where the molecules are farther apart. • This series of compressions and rarefactions is the sound wave that you hear.

4. Sound 1 Sound • The material in which a sound wave moves is called a medium. • Sound waves travel in solids, liquids, and other gases as a vibrating object transfers energy to the particles in the material.

5. Sound 1 Sound • The speed of a sound wave in a medium depends on the type of substance and whether it is a solid, liquid, or gas. • Sound travels slowest in gases and fastest in solids.

6. Sound 1 Amplitude and Energy of Sound Waves • The amount of energy a wave carries corresponds to its amplitude. • More energy is transferred to the medium when the particles of the medium are forced closer together in the compressions and spread farther apart in the rarefactions.

7. Sound 1 Amplitude and Energy of Sound Waves

8. Sound 1 Intensity and Loudness • The amount of energy transferred by a sound wave through a certain area each second is the intensity of the sound wave. • Loudness is the human perception of sound intensity.

9. Sound 1 Intensity and Loudness • Each unit on the scale for sound intensity is called a decibel.

10. Sound 1 Pitch and Frequency • Pitch is the human perception of the frequency of sound waves. • Frequency is a measure of how many wavelengths pass a particular point each second.

11. Sound 1 Pitch and Frequency • Frequency is measured in hertz (Hz). • A healthy human ear can hear sound waves with frequencies from about 20 Hz to 20,000 Hz. • Sound frequencies above 20,000 Hz are called ultrasonic waves. • Infrasonic, or subsonic, waves have frequencies below 20 Hz.

12. Sound 1 Doppler Effect • The change in pitch or frequency due to the relative motion of a wave source is called the Doppler effect.

13. Sound 1 A Moving Source of Sound

14. Sound 1 A Moving Listener • You also can hear the Doppler effect when you are moving past a sound source that is standing still. • The Doppler effect happens any time the source of a sound is changing position relative to the listener.

15. Sound 1 Using Sound • Echolocation is the process of locating objects by emitting sounds and detecting the sound waves that reflect back. • Sonar is a system that uses the reflection of underwater sound waves to detect objects. • Reflected ultrasonic waves are used to examine different body parts.

16. Section Check 1 Question 1 Sound frequencies above 20,000 Hz are called __________ waves. A. infrasonic B. infrared C. subsonic D. ultrasonic

17. Section Check 1 Answer The answer is D. Subsonic and infrasonic are waves with frequencies below 20 Hz.

18. Section Check 1 Question 2 Describe the Doppler effect. Answer The Doppler effect is the change in pitch due to a moving wave source.

19. Section Check 1 Question 3 In which of the following environments would sound waves not travel? A. at altitudes of 10,000 – 15,000 m B. in solid aluminum C. on the Moon D. under water

20. Section Check 1 Answer The answer is C. Sound waves require a medium through which to travel. So, sound waves cannot travel through empty space.

21. Reflection and Refraction of Light 2 The Interaction of Light and Matter Absorption, Transmission, and Reflection • The opaque material in this candleholder only absorbs and reflects light—no light passes through it.

22. Reflection and Refraction of Light • Materials that allow some light to pass through them, like the material of this candleholder are described as translucent. 2 Absorption, Transmission, and Reflection

23. Reflection and Refraction of Light • Transparent materials, such as this candleholder transmit almost all the light striking them, so you can see objects clearly through them. 2 Absorption, Transmission, and Reflection

24. Reflection and Refraction of Light 2 Reflection of Light Regular and Diffuse Reflection • A smooth, even surface such as a pane of glass produces a sharp image by reflecting parallel light waves in only one direction. • Reflection of light waves from a smooth surface is regular reflection. • To cause a regular reflection, the roughness of a surface must be less than the wavelengths it reflects.

25. Reflection and Refraction of Light 2 Regular and Diffuse Reflection • Reflection of light from a rough surface is diffuse reflection. • Diffuse reflection is a type of scattering that occurs when light waves traveling in one direction are made to travel in many different directions.

26. Reflection and Refraction of Light 2 Refraction of Light • Refraction is caused by a change in the speed of a wave when it passes from one material to another.

27. Reflection and Refraction of Light 2 Refraction of Light • Index of refraction is the ratio of the speed of light in a vacuum to the speed of light in the material. • The index of refraction indicates how much the speed of light is reduced in the material compared to its speed in empty space. • The larger the index of refraction, the more light is slowed down in the material.

28. Reflection and Refraction of Light 2 Refraction of Light • White light, such as sunlight, is made up of light waves with range of wavelengths. • Prism refracts the light twice—once when it enters the prism and again when it leaves the prism.

29. Reflection and Refraction of Light 2 Refraction of Light • The longer wavelengths of light are slowed less and are bent the least. • As a result, the different colors are separated when they emerge from the prism.

30. Reflection and Refraction of Light 2 Mirages • Mirages result when the air at ground level is much warmer or cooler than the air above.

31. Reflection and Refraction of Light 2 Mirages • The density of air increases as air cools and light waves move slower in cooler air than in warmer air. • Light waves are refracted as they pass through air layers with different temperatures.

32. Section Check 2 Question 1 What happens to light waves that strike an object? Answer Light waves that strike objects can be absorbed, reflected, or transmitted.

33. Section Check 2 Question 2 What is the difference between refraction and reflection? Answer Refraction occurs if a light wave changes speed in moving from one material to another. Reflection occurs when light waves are returned or thrown back from a surface.

34. Section Check 2 Question 3 __________ material only absorbs and reflects light; no light passes through. A. Transparent B. Translucent C. Opaque D. Mirage

35. Section Check 2 Answer The answer is C. Transparent and translucent materials both allow some light to pass through.

36. Mirrors, Lenses, and the Eye 3 Light Rays Mirrors • A mirror is any surface that produces a regular reflection. Plane Mirrors • A flat smooth mirror is a plane mirror.

37. Mirrors, Lenses, and the Eye 3 Plane Mirrors • Light rays from a light source strike you. • Every point that is struck by the light rays reflects these rays so they travel outward in all directions. • Light rays are reflected from the mirror back to your eyes.

38. Mirrors, Lenses, and the Eye 3 Virtual and Real Images • Plane mirrors always form virtual images. • If light rays from an object pass through the location of the image, the image is called the real image. • If the surface of a mirror is curved inward, it is called a concave mirror.

39. Mirrors, Lenses, and the Eye 3 Virtual and Real Images • The image formed by a concave mirror depends on the location of the object relative to the focal point.

40. Mirrors, Lenses, and the Eye 3 Virtual and Real Images • An object between one and two focal lengths from a concave mirror is real, inverted, and larger than the object. • An object closer than one focal length from a concave mirror produces a virtual image that is upright and larger than the object.

41. Mirrors, Lenses, and the Eye • Reflected rays diverge and never meet, so a convex mirror forms only a virtual image. 3 Convex Mirrors • A mirror that curves outward like the back of a spoon is called a convex mirror. • The image also is upright and smaller than the actual object is.

42. Mirrors, Lenses, and the Eye 3 Lenses • A lens is a transparent object with at least one curved surface that causes light rays to refract. Convex Lenses • A convex lens is thicker in the middle than at the edges.

43. Mirrors, Lenses, and the Eye 3 Convex Lenses • Light rays are refracted toward the center of the lens. • All light rays are refracted so they pass through a single point, which is the focal point of the lens.

44. Mirrors, Lenses, and the Eye 3 Convex Lenses • Lenses with flatter sides have longer focal lengths.

45. Mirrors, Lenses, and the Eye 3 Concave Lenses • A concave lens is thinner in the middle and thicker at the edges. • Light rays that pass through a concave lens bend away from the optical axis.

46. Mirrors, Lenses, and the Eye 3 The Human Eye • Light enters your eye through a transparent covering on your eyeball called the cornea. • The cornea causes light rays to bend so that they converge. • Light then passes through the pupil.

47. Mirrors, Lenses, and the Eye • The retina is the inner lining of your eye, containing light sensitive cells that convert an image into electrical signals. 3 The Human Eye • Behind the pupil is a flexible convex lens.

48. Mirrors, Lenses, and the Eye 3 Brightness and Intensity • The human eye can adjust to the brightness of the light that strikes it. • Light intensity is the amount of light energy that strikes a certain area each second. • Brightness is the human perception of light intensity. • Eyes respond to bright light by decreasing the size of your pupil.

49. Mirrors, Lenses, and the Eye 3 Correcting Vision Problems • If you can see distant objects clearly but can’t bring nearby objects into focus, then you are farsighted.

50. Mirrors, Lenses, and the Eye 3 Correcting Vision Problems • The eyeball might be too short or the lens isn’t curved enough to form a sharp image of nearby objects on the retina.