UNIT 2 - Nature of Waves Flashcards
What are the two basic types of waves
Transverse and Longitudinal
Define transverse waves
Vibrations are 90 degrees to direction of movement
Define longitudinal wave
Vibrations are along direction of movement
Whats a progressive wave
Transfers energy from one place to another with no net movement of particles/material
What are mechanical waves
Waves that travel through a medium
3 examples of transverse waves
Water waves
Electromagnetic waves
S-waves (seismic)
3 examples of longitudinal waves
Sound waves
Ultrasound waves
P-waves (seismic)
Define the amplitude
Maximum displacement of a wave from equilibrium
Symbol (A)
Unit (metres, m)
Define wavelength
The distance between adjacent peaks of a wave, (distance between adjacent points on a wave that are in-phase)
Symbol (λ)
Unit (metres, m)
Define frequency
Number of wavelengths passing a point per unit time
Symbol (f)
Units (Hertz, Hz)
Define Hertz (Hz)
1 Hz is 1 wavelength passing a point per second
Define period
Time taken for a wave to make one complete oscilation
Symbol (T)
Unit (seconds, s)
Define wave displacement
Distance and direction of a vibrating particle in a wave measured from its undisturbed position
Symbol (y)
Units (metres, m)
What does phase mean
The position of a point on a wave in terms of its position in the wave cycle
What does in phase mean
2 or more points are vibrating in exactly the same way with same displacement.
What does antiphase mean?
When 2 or more points are vibrating exactly out of phase, with exactly opposite displacements.
Difference between antiphase and out of phase
Antiphase is when 2 or more points are EXACTLY out of phase
Out of phase is not in phase by some fraction of a wave cycle
What is phase angle
Used to show exactly the phase of vibration of particles within a cycle of oscillation. The angle can be measured in either degrees or radians
What is phase difference
The amount by which waves are out of phase. Measured in radians or degrees
How can waves be created in a water tank
By using a plane dipper or rod dipper vibrating on the surface of water in a tank
What are wavefronts
The straight or circular lines which travels away from the source of the waves
All points along the wave front are therefore oscillating in phase
How is the direction of propagation shown
With a line which is at right angles to the wavefront
What is wave velocity
Wave velocity = frequency x wavelength
V = f x λ
What is a plane polarised wave
A wave is plane polarised if the particles or electromagnetic field oscillates in a single plane. This is a property of transverse waves.
What is polarisation
Process of turning an unpolarised wave into a plane polarised wave through the use of a polarising filter
How does polarisation work (1 filter)
The polarising filter lets light with the same plane of polarisation through, and all other waves are absorbed.
Eg. Vertical oriented polarising filter will let through the light oscillating in the vertical direction, and all other waves get absorbed
How does polarisation work with 2 polarising filters 90 degrees to eachother?
the first polariser will let through the light with same plane of polarisation only and absorb the rest of the waves, and then the second polariser absorbs the light that was let through because it is oriented 90 degrees to the first polariser. So no light is let through.
0 intensity
I = 0
What is an unpolarised wave
Vibrations in many planes
What happens if light goes through two polarisers of the same plane as each other are used
The polarisers are same orientation so the light that oscillates in the same plane as the polarisers will pass through both. There will be a plane polarised eave transmitted with maximum intensity.
Imax
What happens to light if it passes through a vertically oriented polariser and a second polariser rotated at an angle θ
The light with same plane of polarisation goes through the first polariser, then some of it will pass through the second rotated polariser because its at an angle What happens to light if it passes through a vertically oriented polariser and a second polariser rotated at an angle θ
Intensity is reduced
What is malus’ law
I=Imax cos² θ
THIS IS GIVEN so ye idk
List 2 practical uses of polarisation
- Used in sunglasses to reduce intensity of light
- 3D cinema glasses, one lenses is verticle plane, other lenses is horizontal plane.
Define diffraction
The spreading out of waves when they meet obstacles such as the edges of a slit. Some of the waves energy travels into geometrical shadows of the obstacles
