Sound. sound waves - compressional waves formed from vibrating objects colliding with air molecules.

Transcription

1 Sound sound waves - compressional waves formed from vibrating objects colliding with air molecules. *Remember, compressional (longitudinal) waves are made of two regions, compressions and rarefactions. 1

2 speed of sound - depends on temperature and state of the medium Sound travels faster in solids and liquids because the molecules are closer together than gas molecules. As the temperature of a medium rises, molecules move faster allowing sound waves to travel faster. 2

3 Human Hearing - involves 4 stages: Stage 1: ear gathers compressional waves which vibrate a tough membrane called the eardrum. Stage 2: the middle ear has three bones called hammer, anvil, and stirrup which amplify sound waves. Stage 3: the inner ear contains the cochlea, which vibrates, sending auditory nerve impulses to the brain. Stage 4: the brain decodes and interprets nerve impulses as sounds. 3

4 intensity - amount of energy that flows through a certain area in a given amount of time. loudness - human perception of intensity, measured in decibels (db) pitch - how high or low a sound seems to be, which is related to frequency Humans can hear 20-20,000 Hz Infrasonic < 20 Hz Ultrasonic > 20,000 Hz 4

5 Music and the Uses of Sound music - made of sounds that are deliberately used in a regular pattern sound quality - differences among sounds of the same pitch and loudness This is why a piano sounds different than a flute playing the same note. 5

6 Instruments: Each instrument has a set of natural frequencies at which it will vibrate, called overtones, and produce an instrument s distinct sound quality. Instruments use resonators, or hollow chambers that amplify sound when air inside vibrates. Example: brass and woodwinds - mouthpiece guitars and violins - hollow body drums - inside and sides 6

7 acoustics - the study of sound Uses of sounds Ex. concert hall architects and engineers echolocation - process of locating objects by emitting sounds and interpreting the reflected sound waves Ex. bats 7

8 sonar - system that uses the reflection of underwater sound waves to detect objects Ex. fishing boats ultrasound - high frequency sound waves Ex. medicine - pregnancy, breaking up kidney stones 8

9 Reflection and Refraction of Light Objects must reflect light in order to be seen. Opaque does not allow light to pass through Only absorbs and reflects Translucent Some light passes through Transparent Transmits almost all light Absorbing and reflecting light very little 9

10 Law of reflection - the angle of incidence (i), or where light strikes a surface, is equal to the angle of reflection (r ). Regular (specular) reflection Diffuse reflection 10

11 Refraction of light - occurs when a wave of light passes from one medium to another and the light wave is bent or refracted. Index of refraction - indicates how much a material reduces the speed of light; the more the light is slowed, the greater the index of refraction. 11

12 Mirrors Light is necessary for eyes to see - light waves spread in all directions from a light. Mirror - smooth surface that reflects light to form an image. Plane mirror - Flat, smooth mirror in which an image appears upright. Concave mirror - mirror surface is curved inward; image depends upon the location of the object relative to the focal point. Convex mirror - mirror curved outward; diverges light rays when reflected and show virtual images. 12

13 Mirror Shape Position of Object Image Type Image Orientation Size Plane Any position virtual upright Same as object Concave More than 2 focal lengths away Between 1 and 2 focal lengths Within the focal length real Upside down Smaller than object real Upside down Larger than object virtual upright Larger than object Convex Any position virtual upright Smaller than object 13

14 Lenses and Optical Instruments Lens - transparent material with a curved surface that refracts or bends light rays 14

15 Lens Shape Location of Object Image Type Image Orientation Size convex concave Beyond 2 focal lengths Between 1&2 focal lengths Within 1 focal length Object at any position real inverted Smaller than object Real inverted Larger than object virtual upright Larger than object virtual upright Smaller than object 15

16 The structure of your eye allows you to focus on objects. Light enters the eye through the cornea - a transparent covering on the eyeball. A convex lens helps to focus light rays to form images. The retina, or inner lining of the eye converts light into electrical signals that the brain interprets. 16

17 Telescopes - use mirrors and lenses to gather more light from far away objects than the eye does. Microscopes - use two convex lenses with short focal lengths to magnify small, close objects. Cameras - gather and bend light with a lens to form an image on light-sensitive film or digital storage disk. 17