WAVES NOTES

  1. A wave is a disturbance that travels through matter or space, carrying energy.
  1. Waves can travel through solids, liquids and gases.
  2. Some waves travel through empty space.
  3. The matter or space through which a wave travels is called a medium. The medium vibrates when a wave is generated by a source of energy.
  1. Types of Waves: The two main groups of waves are based on the direction of the wave motion and the direction of the wave disturbance.
  1. Transverse waves – disturbance occurs at right angles (perpendicular) to the direction of the wave motion.
  2. Electromagnetic waves (light waves, radio waves, X-rays)
  3. The electromagnetic spectrum is the continuous range of electromagnetic waves place in order of increasing frequency. Light waves are part of the electromagnetic spectrum.
  4. Light has many of the properties of waves. But light can also act as though it is a stream of particles.
  5. The shorter the wavelength on the electromagnetic spectrum, the more dangerous the waves.
  6. Wireless communication (pp. 222-229).
  7. Using light (pp. 259-268).
  8. Water waves
  1. Longitudinal waves – disturbance occurs back and forth (parallel) along the direction of the wave motion. Compressions occur where the medium is close together, and rarefactions occur where the medium is spread apart.

Sound waves – the common medium for sound is air, but it can travel through solid and liquid. Sound waves do not travel in the vacuum of space. The speed of sound waves depends on the elasticity, density and temperature of the medium.

  1. Sound travels faster in more elastic materials.
  2. Sound travels faster in solids.
  3. Sound travels slower in denser materials.
  4. Sound travels slower at lower temperatures.

Supersonic is “faster than the speed of sound”. (p. 166)

  1. Surface waves – combinations of transverse and longitudinal waves.
  1. Doppler Effect: The change in frequency as a wave source moves in relation to the listener. (p. 172-173)
  1. Characteristics of Waves
  1. The highest point of the wave is the crest.
  2. The highest point of the wave is the trough.
  3. The height of a wave is the amplitude (measured in meters). The greater the amplitude, the more energy the wave has.
  4. The distance from one crest of a wave to the next is called the wavelength.
  5. The frequency of a wave is the number of crests that pass a point in a second. It is also the number of vibrations per second. Frequency is measured in hertz (Hz): One hertz equals one wave per second or one vibration per second.
  6. Wavelength and frequency are related to the speed or velocity.
  7. Velocity = wavelength x frequency
  1. v = w x f
  1. A material that reflects or absorbs all of the light that strikes it is opaque.
  2. A transparent material transmits light allowing the viewer to see through it.
  3. Translucent materials scatter light as the light passes through. Details of the material cannot be clearly seen.
  1. Wave change: This occurs when waves encounter a barrier, when a medium changes, or when waves encounter other waves.
  1. Reflection is the bouncing back of a wave when it hits a boundary.
  1. The angle at which a wave hits a surface is called the angle of incidence.
  2. The angle at which it is reflected is called the angle of reflection. The angle of incidence equals the angle of refection.
  3. The bending of waves around the sides of a barrier is called diffraction.
  1. The speed of a wave changes when the wave medium changes. This change in speed can cause the wave to bend. The bending of waves due to a change in the medium is called refraction. The amount of refraction depends on:
  1. – how much the speed of the wave changes when it enters the new medium.
  2. – the angle of incidence – the sharper the angle of incidence, the greater the refraction.
  1. The combined effect of two or more waves coming together is called interference. This can cancel or add energy.
  1. Constructive interference occurs when waves combine (add energy) to make a wave with larger amplitude.
  2. Destructive interference occurs when the amplitudes of two waves combine (cancel energy) to produce smaller amplitude.
  1. If the incoming wave and the reflected wave combine at the right place, the combined wave appears to be standing still. This is a standing wave.