Topic 3b - Properties of waves

How is a sound wave generated

Particles move to cause pressure, which travels out in waves

How does a sound wave travel through air?

Particles bump into each other, transferring energy in waves

Infrasound

Sound below the range of human hearing (below 20Hz)

Ultrasound

Sound that is above the range of human hearing (above 20kHz)

What does energy not transfer? Why?

Mass, because particle oscillate, changing areas of pressure but ultimately staying in the same place

Why do sound waves require a medium to travel through, but light waves do not?

Sound waves rely on particles changing pressure, whereas lightwaves are not particles and do not require them

What can travelling waves all do

Reflection, refraction, diffraction, interfere

Reflection

Bounce back from a surface

Refraction (of waves)

Change speed and direction as they enter a medium which has a different density

Diffraction (of waves)

Spread out as they pass through a gap

Interfere (waves)

Two sources cancelling out, such as a trough and a peak cancelling out to make a flat area

Vibration

Periodic back and forth motion of particles

What are the two types of waves

Transverse and longitudinal

What direction are oscillations in a transverse wave compared to the direction of energy transfer?

Perpendicular

What direction are oscillations in a longitudinal wave compared to the direction of transfer?

Parallel

Example of a transverse wave

A person attaching a rope to a wall and swinging it up and down

Example of a longitudunal wave

moving a slinky from side to side whilst the slinky is laying flat

Amplitude

Height of the ave

Wavelength

Length of the wave

Peak

Highest point in the wave

Trough

The lowest point in the wave

Equilibrium line

A line which represents the position of the particles when they are stationary

Frequency

How many waves pass a point in a second

Wavefront

The crest of the wave

Example of a wave being reflected (2)

Water hitting a wall, light bouncing off a mirror

Doppler effect

When an object is moving, the sound heard by an observer is different to that produced, as the moving object begins to catch up with its own sound waves

Example of the doppler effect

When the frequency of an ambulance siren seems to change as it moves towards and away from us

What is the doppler effect when an object moves closer?

As the source and the observer move together the space between the waves decreases, and so does the distance between wave fronts. this decreases the relative wavelength, increasing the frequency, making the sound become higher.

What is the doppler effect when things move apart?

The space between waves increases, and so does the distance between wavefronts, increasing the relative wavelength. therefore the frequency decreases, so a sound becommes lower.

What happens to colours due to the doppler effect when things move closer

Green light shifts to the blue end of the spectrum

What happens to colours due to the doppler effect when things move further apart

Green light shifts to the red end of the spectrum

Propagate

The direction in which the energy of a wave moves