Chapters 25,27,28

Chapters 25,27,28

1. 25.1

   • A repeating back-and-forth motion about an equilibrium position is a vibration.
   • Vibrations cause disturbances that are transmitted progressively from one place to the next with no actual transport of matter—a wave.

2. 25.2

   • The high points on a wave are called crests. The low points on a wave are called troughs.
   • The term amplitude refers to the distance from the midpoint to the crest (or trough) of the wave.
   • The wavelength of a wave is the distance from the top of one crest to the top of the next one.
   • Amplitude tells you how much energy a wave has
   • Frequency tells you how quickly a wave vibrates
   • The frequency of the vibrating source and the frequency of the wave it produces are the same. The unit of frequency is called the hertz (Hz).

3. 25.3

   • The energy transferred by a wave from a vibrating source to a receiver is carried by a disturbance in a medium.
   • Most information gets to us in some form of a wave. Sound is energy that travels to our ears in the form of a pressure wave of compressed air. Light is energy that comes to our eyes in the form of a different kind of wave (an electromagnetic wave). The motion of the Earth we feel in earthquakes comes in waves. The signals that reach our radio and television sets also travel in the form of electromagnetic waves.

4. 25.4

   • You can calculate the speed of a wave by multiplying the wavelength by the frequency.
   • If the wavelength is 3 meters and if two crests pass a stationary point each second, then 3 meters × 2 waves pass by in 1 second.The waves therefore move at 6 meters per second.

5. 25.5-25.6

   • Whenever the motion of the medium is at right angles to the direction in which a wave travels, the wave is a transverse wave. (light)_
   • When the particles oscillate parallel to or along the direction of the wave, the wave is a longitudinal wave. (sound)
   • sound cannot travel through empty space but light can

6. 27.1

   • Almost everything we see is made visible by the light it reflects.
   • you can not move faster than something that has no inertia (the speed of light)
   • Some materials, such as air, water, or window glass, allow light to pass through. this means it is translucent Other materials, such as thin paper or frosted glass, allow the passage of light in diffused directions so that we can’t see objects through them. these things are opaque

7. 27.3

   • This energy travels in a wave that is partly electric and partly magnetic. Such a wave is an electromagnetic wave.
     • The waves that make up light travel at 3x108m/s. The speed of light, c, is the fastest speed possible.
   • The lowest frequency of light we can see appears red. The highest visible light, violet, has nearly twice the frequency of red light.
   • E=hf e is the energy of a single photon of light in J f is the frequency in hertz h is planaks constant (6.6 x 10 -34 Jxs)

8. 27.4

   • as light passes from air through a lens, its path is bent
   • a light wave incident upon a plane of glass sets up vibrations in the atoms. Because of the time delay between absorptions and remissions the average speed of light in glass is less than c. depending on the medium you get different speeds of light
   • the denser the medium the slower the light travels
   • but with sound the denser the object the faster the sound travels
   • the brightness of light is similar to the force between electric charges ass you move farther from light the light decreases by the square of its distance b- 1/d squared as the light spreads out it becomes less dense

9. 28.2

   • light reflects from objects similar to the way sound “reflects” from a tuning fork when another sets in into vibration
   • the colors of most object around you are due to the way objects reflect light

10. 28.3 -28.5

    • a red piece of glass appears red because REFLECTS RED LIGHT BACK AND ABSORBS ALL OTHER COLORS
    • when red light , green light and blue light of equal brightness are projected in a white screen the overlapping are at appear different colors
    • you can almost make any color at all by overlapping red,green and blue by adjusting the brightness or saturation of each