Physical World/Waves

• Heat energy is transferred via conduction, convection and radiation
• Sound and light energy can also be transferred, and they transfer through waves
• Wave


  A regular periodic disturbance in a medium or space
• Sound wave


  • At a concert, the speakers blast sound energy out in waves, which travel through the air to our ears. The air particles experience a periodic disturbance and oscillate back and forth.
• Two Main Types of Waves


  • Mechanical waves
  • Electromagnetic waves
• Mechanical waves

  Travel through a medium, and the substance of this medium is deformed. Example: Sound, water waves, earthquakes
• Electromagnetic waves


  Do not require a medium. Instead, they consist of periodic oscillations of electrical and magnetic fields generated by charged particles. Therefore, they can travel through a vacuum. Example: Light, microwaves, radio waves.
• Waves transfer energy but not matter
• Transverse waves


  Particles move perpendicular to the direction of wave propagation
• Longitudinal waves


  Particles move parallel to the direction of wave propagation
• All waves have a source of energy, which involves vibration of some sort, particles that vibrate, a means by which the energy can propagate outwards, and speed or velocity of the wave
• Wavelength


  The distance between successive waves
• Displacement


  The distance a particle in the wave is from the rest position
• Amplitude


  The maximum distance that a particle moves from its rest position
• Frequency


  The number of oscillations per second, measured in Hertz
• Period


  The time taken for one full oscillation to take place
• Frequency and period


  They are related by the equation f = 1/T
• Velocity of a wave


  Depends on the medium, generally the more elastic the medium the faster the wave moves. Can be calculated as v = f * λ or v = s / t
• The wave equation relates frequency, velocity, and wavelength
• Sound waves are the result of vibrations or oscillations of particles in a medium
• Sound waves can propagate as a longitudinal wave motion in 3-D away from the source
• Audible sound waves


  Range in frequency from 20 Hz to 20 kHz
• Ultrasound


  Sound waves with a frequency too high for the human ear to hear
• Infrasound


  Sound waves with a frequency too low for the human ear to hear
• Amplitude of a sound wave


  The greater the energy of the wave, the greater the amplitude
• Volume/loudness of a sound


  Increases with the amplitude of the waves, but is also affected by frequency due to the varying sensitivity of the human ear
• When a sound wave meets a boundary between two media, some of the energy of the wave will be reflected at the boundary
• Knowing the speed of sound in a particular medium, the distance to a reflecting surface can be determined, as used in SONAR
• Electromagnetic waves travel as a pair of interacting electrical and magnetic waves, with the planes of the waves perpendicular to the propagation direction
• Types of Electromagnetic Radiation


  • Radiowaves
  • Microwaves
  • Infrared
  • Visible Light
  • Ultraviolet Light
  • X-rays
  • Gamma Rays
• Electromagnetic waves are the only type of wave capable of travelling through a vacuum
• Light travels in straight lines at a very fast speed of 3.0x10^8 m/s
• Light travels much faster than sound
• We see things because they reflect light into our eyes
• The sun provides the energy that enables life on Earth
• Light


  • Travels in straight lines
  • Travels much faster than sound
  • We see things because they reflect light into our eyes
• Light travels at 3.0 x 10^8 m/s
• A light-year is not a measurement of time
• Nothing moves faster than the speed of light
• Light is transferred through radiation (via electromagnetic waves) in a vacuum