• Energy is transferred through moving?oscillations?or?vibrations. These can be seen in vibrations of ropes or springs

Waves can be shown through vibrations in ropes or springs

• The oscillations/vibrations can be perpendicular or parallel to the direction of wave travel:
  • When they are?perpendicular, they are?transverse?waves
  • When they are?parallel, they are?longitudinal?waves

Ripple tanks

• Waves can also be demonstrated by ripple tanks. These produce a combination of transverse and longitudinal waves

Wave effects can be demonstrated using a ripple tank

• Ripple tanks may be used to demonstrate the wave properties of reflection, refraction and diffraction

• Displacement (x)?of a wave is the distance from its equilibrium position. It is a vector quantity; it can be positive or negative
• Amplitude (A)?is the maximum displacement of a particle in the wave from its equilibrium position
• Wavelength (λ)?is the distance between points on successive oscillations of the wave that are in phase
  • These are all measured in?metres (m)

Diagrams showing the amplitude and wavelength of a wave

• Period (T)?or time period, is the time taken for one complete oscillation or cycle of the wave. Measured in?seconds (s)

Diagrams showing the time period of a wave

• Frequency (f)?is the number of complete oscillations per unit time. Measured in?Hertz?(Hz)?or?s^-1

Frequency equation

• Speed (v)?is the distance travelled by the wave per unit time. Measured in?metres per second?(m s^-1)

Phase

• The phase difference tells us?how much a point or a wave is in front or behind another
• This can be found from the relative positive of the crests or troughs of two different waves of the same frequency
  • When the crests or troughs are aligned, the waves are?in phase
  • When the crest of one wave aligns with the trough of another, they are in?antiphase
• The diagram below shows the green wave?leads?the purple wave by ? λ

Two waves ? λ out of phase

• In contrast, the purple wave is said to?lag?behind the green wave by ? λ
• Phase difference is measured in?fractions of a wavelength, degrees?or?radians
• The phase difference can be calculated from two different points on the same wave or the same point on two different waves
• The phase difference between two points:
  • In phase?is?360^o?or 2π radians
  • In anti-phase?is?180^o?or π radians

• Waves transfer energy between points, without transferring matter
• When a wave travels between two points, no matter actually travels with it:
  • The points on the wave simply vibrate back and forth about fixed positions
• Waves that transfer?energy?are known as?progressive?waves
• Waves that do not transfer energy are known as?stationary?waves