Progressive and stationary waves

What is a progressive wave?

A wave that transfers energy from one point to another without transferring the medium itself.

What are the properties of a progressive wave?

Amplitude, wavelength (on a displacement, distance graph)

Time period (the same placing as wavelength but on a displacement, time graph)

Frequency

What is the equation for time period?

T=1/f

What is the equation for wavespeed?

v = fλ

What is phase difference?

The difference in position within a wave cycle between two waves. When crests and troughs are aligned the waves is in phase, when the crest of one wave aligns with the trough from another they are in antiphase.

What is a transverse wave?

A wave in which the particles oscillate perpendicular to the direction of the wave travel, (electromagnetic, waves on a string).

What are longitudinal waves?

A wave in which the particle oscillates parallel to the direction of the wave travel, (sound waves, ultrasound). They show areas of compression and rarefactions.

What is polarisation?

When particle oscillations occur in only one of the directions perpendicular to the direction of wave propagation.

Can longitudinal waves be polarised?

No, only transverse waves can be polarised.

Using polarising filters, how can you get the maximum intensity of light transmitted?

Place an unpolarised light source in front of two identical polarising filters, A and B with their transmission axes parallel. Filter A will polarise the light in a certain axis, all of the polarised light will pass through filter B unaffected.

Using polarising filters, how can you get the minimum intensity of light transmitted?

Place an unpolarised light source in front of two identical polarising filters, A and B with their transmission axes perpendicular to eachother. Filter A will polarise the light in a certain axes, none of the polarised light will pass through filter B.

How do polaroid sunglasses work?

When light is reflected from a reflective surface, it undergoes partial plane polarisation. Polaroid glasses do not allow any horizontally polarised light to pass through, therefore they are useful in reducing the glare on the surface of the water.

What are stationary waves?

Waves produced by the superposition of two waves, the peaks and troughs do not move, they store energy.

What are the differences between progressive and stationary waves?

In progressive waves all points have the same amplitude, in a stationary waves each point has a different amplitude. In progressive waves points exactly a wavelength apart are in phase, in stationary waves points between nodes are in phase and points on either side of a node are out of phase. In progressive waves energy is transferred, in stationary waves energy is stored.

What are nodes and antinodes?

Nodes are regions of destructive inteference where there is no vibration, antinodes are regions of constructive inteference where the vibrations are at their maximum amplitude. Nodes are fixed and antinodes only move in the vertical direction.

What is constructive inteference?

When two waves in phase superpose and the resultant wave has double the amplitude.

What is destructive inteference?

When two waves in antiphase superpose and the resultant wave has no amplitude.

What conditions are needed for superposistion?

The waves must have the same wavelength, a similiar amplitude, the same frequency and be travelling in opposite directions along the same line.

How can microwaves be used to demonstrate stationary waves?

A microwave source is placed in line with a reflecting plate and a small detector between the two. By moving the detector it can pick up minima (nodes) and maxima (antinodes) of the stationary wave pattern.

Regarding harmonics, what is the equation for wavelength when n=1,2,3?

λ=2L/n

Regarding harmonics, what is the equation for wavelength when n=odd?

λ= 4L/n

What is the speed of a wave travelling along a string with two fixed ends given by?

v = √ T/µ

T= tension

µ= mass per unit length

What is the equation for the frequency of the first harmonic?

f=1/2L √ T/µ

What is the distance between adjacent nodes or adjacent antinodes equal to?

Half a wavelength.

What is the distance between an adjacent antinode and node equal to?

A quarter of a wavelength.