Chapter 15

1
Chapter 15 Characteristic of Waves

• Learn the language of waves
• Wave a disturbance that transfers energy from
  place to place
• Medium material that the wave travels in
• Water wave water
• Sound wave solid, liquid, or gas (air)
• Mechanical waves waves that require a medium
  to travel through
• The medium does not travel along with the wave.
• Water moves up and down while the wave moves past.

2

• Amplitude height of wave
• Wavelength (?) distance between two
  corresponding parts of a wave (crest to crest)

3

• Vibration repeated back and forth or up and
  down motion that can create waves.
• Transverse wave a wave that has crests and
  troughs
• Example a water wave

4

• Longitudinal wave a wave that has compressions
  and rarefactions
• Example a sound wave

5

• Frequency is the number of waves
  made each second. (f waves/sec.)
• Frequency is also the number of waves
  that pass a given point each second.
• 1 wave/sec 1 hertz (Hz)
• Speed wavelength (frequency)
• Speed
• Frequency
• Wavelength
• Speed
• Wavelength
• Frequency

6

• Example problem The speed of a wave on a
  guitar string is 100 m/s and the frequency is
  1,000 Hz. What is the wavelength of the wave?

7
Interactions of waves

• Reflection waves can bounce off an object
  (like light off a mirror).
• The angle of incidence the angle between the
  wave and an imaginary line.
• The angle of incidence the angle of
  reflection.

the normal
Light
Mirror
8

• Refraction When light moves from one medium
  into another it changes speed which causes it to
  bend.
• As the wave slows down it is bent towards the
  normal.
• As the wave speeds up it is bent away from the
  normal.

Light ray
Air
Water
9

• Diffraction when a wave passes a barrier or
  moves through a hole in a barrier it bends and
  spreads out.

Waves
10
Waves can add or cancel
11
Wave Interference

• http//id.mind.net/zona/mstm/physics/waves/interf
  erence/intrfrnc.html

12

• Constructive interference adding of waves
• Destructive interference canceling of waves
• Standing waves- when a reflected wave adds to an
  incoming wave just right a stationary wave is
  produced.
• Nodes stationary points of standing waves
• Antinodes crests and troughs of a standing wave

13
Resonance

• Most objects have a natural frequency of
  vibration.
• Resonance is when the vibration passing
  through the object matches the objects natural
  vibration. (like pushing a child on a
  swing. Energy input adds perfectly.)