Types of waves
Waves are one of the ways in which energy may be transferred between stores. Waves can be described as The repeated and regular fluctuations, above and below the same position, eg the pressure of a sound wave or the voltage of an alternating current., or Repeated movements back and forth (about a fixed point). about a rest position. For example:
- sound waves cause air particles to vibrate back and forth
- ripples cause water particles to vibrate up and down
The direction of these oscillations is the difference between longitudinal and transverse waves. In A wave that moves in the same direction as the direction in which the particles are vibrating., the vibrations are parallel to the direction of wave travel. In A wave that moves in a direction at right angles to the way in which the particles are vibrating., the vibrations are at right angles to the direction of wave travel.
Mechanical waves cause oscillations of particles in a solid, liquid or gas and must have a A material through which a wave can be transmitted (propagate). to travel through. Electromagnetic waves cause oscillations in electrical and magnetic fields.
It is important to remember that all waves transfer energy but they do not transfer Sub-atomic particles and anything made from them, such as atoms and molecules, are matter. Energy and forces are not matter.. For example, if a ball is placed on the surface of a pond when ripples move across it, the ball will move up and down but not outwards with the wave. Similarly, when sound waves move through the air to a person's ear, the air itself does not move - instead the sound is transferred through the vibrating molecules, which stay where they are and vibrate about a fixed point.
Parts of a wave
Waves are described using the following terms:
- Peak - the highest point above the rest position.
- Trough - the lowest point below the rest position.
- Amplitude - the maximum displacement of a point of a wave from its rest position.
- Wavelength - the distance covered by a full cycle of the wave. Though usually measured from peak to peak or trough to trough, it can be measured between any two points of identical displacement.
- Time period - the time taken for a full cycle of the wave. Usually measured from peak to peak, or trough to trough.
- Frequency - the number of waves passing a point each second.
- Frequency (f) = 1 ÷ time period (T).
