3.1 - Longitudinal & Transverse Waves : Waves Flashcards
What is a progressive wave?
A wave that transfers energy from one point to another without transferring the medium itself.
What is the displacement of a wave? (x)
The distance of a point on the wave from its equilibrium position.
What is the amplitude of a wave? (A)
The maximum displacement of a particle in the wave from its equilibrium position.
What is the wavelength of a wave? (λ)
The distance between points on successive oscillations of the wave that are in phase. (a full oscillation).
what is time period? (T)
The time taken for one complete oscillation or cycle of the wave. (Time for one wavelength to pass a point).
What is frequency?
The number of complete oscillations per unit time. (Hz)
What is the frequency-period equation?
f = 1/T (Frequency = 1/ Time period)
(Also written as T = 1/f)
What is the speed of a wave equation?
c = fλ
Speed of a wave = frequency x wavelength
What does the speed of a wave equation show?
- As the wavelength increases, the frequency decreases
- As the wavelength decreases, the frequency increases
What does a longitudinal wave do?
Particles in the medium oscillate parallel to the direction of the wave’s propagation (travel).
What does a transverse wave do?
Particles in the medium oscillate perpendicular to the wave’s propagation (travel).
What is phase difference?
A measure of how much a point or a wave is in front or behind another.
How can you tell if waves are in phase?
The crests or troughs are aligned.
How can you tell if waves are antiphase?
When the crest of one wave aligns with the trough of another.
How can phase difference be described with degrees/radians?
In phase = 360° or 2π radians
In anti-phase = 180° or π radians
Example - calculate the ‘lag’ between the waves if there is a phase difference of 1/4λ.
1/4λ x 360 = 90° or
1/4λ x 2π = π/2
What are 3 examples of transverse waves?
- Electromagnetic waves (like: radio, visible light and UV)
- Vibrations on a guitar string
- Seismic (S) waves
What are 3 examples of longitudinal waves?
- Sound waves
- Ultrasound waves
- Seismic (P) waves
What is a rarefaction?
A region in a longitudinal wave where the particles are furthest apart.
What is a compression?
A region in a longitudinal wave where the particles are closest together.
What type of wave can be polarised?
Transverse waves.
What is the wavelength on a longitudinal wave?
Distance between 2 compressions or rarefactions.
What is the wavelength on a transverse wave?
Distance between 2 peaks or troughs.
What is polorisation?
When particle oscillations occur in only one of the directions perpendicular to the direction of wave propagation.
Why does polarisation only occur in transverse waves?
Because transverse waves oscillate in any plane perpendicular to the propagation direction.
What happens when transverse waves are polarised?
- Vibrations are restricted to one direction
- These vibrations are still perpendicular to the direction of propagation / energy transfer
What is the direction of propagation?
The direction of the wave’s travel.
What happens when you vertically polarise a transverse wave?
The wave only oscillates in one direction.
What happens when you have 2 polarising filters, one vertical and one horizontal? (filters are perpendicular to each other)
The first filter will polarise the light and the second filter will stop all waves passing through.
Why do you have to line up transmitting and receiving television aerials?
TV signals are polarised by the orientation of the rods on the broadcasting aerial. You must line up the roads on the receiving and transmitting aerial to get a better signal.
What is partial plane polarisation?
This means if the surface is horizontal, a proportion of the reflected light will oscillate more in the horizontal plane than the vertical plane.
What is an example of partial plane polarisation?
When light is reflected from a reflective surface like the surface of water or a wet road.
How do polaroid sunglasses reduce glare?
They contain vertically oriented polarising filters which block out any horizontally polarised light. Partial plane polarisation occurs on reflective surfaces and they oscillate more on the horizontal plane. This will reduce glare from reflective surfaces.
