WAVES

Wave - a periodic disturbance that propagates energy through a medium or space, without a corresponding transfer of matter.

e.g.1 sound wave (regular variation in pressure)

e.g. 2 light wave ( regular variation in the strength or direction of magnetic and electric fields)

              

 

crest

trough

amplitude

Equilibrium position

wavelength

Parts of a Wave

Crest – an upward displacement that is created in a medium as a wave passes by

Trough – a downward displacement that is created in a medium as it passes by

Amplitude – the maximum distance from the equilibrium position which the particles of the medium are displaced as the waves passes by

Wavelength – this is the distance between any particle on a wave and the nearest particle that is in phase with it. The symbol is (Greek letter lambda)

Mechanical Waves

Waves that travel through a material medium

e.g. water, sound, seismic, slinky

i.e. not electromagnetic

Motion in a Wave

• As a wave moves through a medium (say a rope) the particles move perpendicular to the motion (propagation) of the wave.

• This is known as a transverse wave

In a transverse wave, we would say that points A & B are “in phase”. They are points 1 wavelength apart and are moving in the same direction at the same speed.

Longitudinal or Compression Waves

Waves in which the displacement of the particles in the medium are parallel to the direction of the motion of the wave.

Animations – types of waves

Continuous waves – displacements that occur at regular intervals (e.g. 5 waves / second)

Pulse – a single displacement

Frequency (f) – the number of displacements or cycles per second (unit is Hertz – Hz)

e.g 5 waves per second = 5 Hz

Period (T) – the time between the passage of two successive crests past a given point.

-the amount of time for one cycle to complete

-Units are units of time (s, min, hr, day, etc)

Frequency and period are inverses of each other

fT

1

The Universal Wave Equation

Given the diagram below

The wave travels the distance in one period (T)

Recall the equation for velocity

t

dv

f

fT

v

1

fv

Sample Questions