Waves Flashcards
What is a wave?
Where energy is transferred some distance without any transfer of material between the two points.
Amplitude
The maximum displacement of particles from equilibrium
Wavelength
The distance between adjacent particles vibrating in phase
Frequency
Number of waves passing a point / being given out by the sourse each second
Time period
Time for a wave particle to do one cycle
In phase
Where two waves are at the same point in their cycles at the same time
Antiphase
Where two waves are half a cycle out of phase
Transverse waves
Particles vibrate at right angels to the direction of energy transfer
What is an EM wave?
A disturbance in the electric and magnetic field (these are perpendicular to each other and are always in phase)
Properties of Em waves
- Can travel through a vacuum
- All travel at the speed of light in a vacuum
EM waves in order of increasing wavelength (decreasing frequency)
Gamma
X-ray
UV
Visible
Infra-red
Micro
Radio
Longitudinal waves
Vibrations are parallel to the direction of propagation of the wave
Polarised light
Vibrates in only one direction perpendicular to the direction of travel of the light
Unpolarised light
Vibrates in all directions perpendicular to the direction of travel of the light
How can light be polarised?
With a polarising filter which polarises the light in one direction
How can you distinguish between longitudinal and transverse waves?
Polarisation.
Only transverse waves can be polarised
Which direction are fishermen’s glasses polarised in?
Polarised in the vertical direction to block light that is horizontally polarised by reflecting off the water
Superposition
When two waves meet the total displacement at a point is equal to the sum of the individual displacements at that point
What happens when two waves meet and are in phase with each other?
Reinforcement (constructive interference)
What happens when two waves meet and are in anti-phase with each other?
Cancellation (destructive interference)
Conditions for stationary / standing waves to form
Two waves must:
- Be moving in opposite directions
- Have the same frequency
- Have similar amplitudes
- Meet and superpose
Nodes
Points where the displacement is always 0, waves meet in anti-phase and destructively interfere.
Distance between two nodes or two anti-nodes
1/2 a wavelength
Antinodes
Points where the amplitude of vibration is at its maximum, waves meet in phase and constructively interfere.
Phase difference between two nodes
0 radians (in phase)
Phase difference either side of a node
π radians (antiphase)
Where are the nodes/antinodes of the harmonics on a string?
There is a node at each end
Length of the 1st harmonic on a string / pipe with open ends
λ/2
Length of the 1st harmonic in a pipe with one closed end
λ/4
Why do microwave have turntables?
This moves the food through the nodes (no energy transfer) and antinodes (maximum energy transfer) to ensure it is evenly cooked.
Features of progressive waves
- Energy is transferred
- Adjacent particles vibrate out of phase
- Adjacent particles have the same amplitude
Features of standing waves
- Energy is trapped in one place
- Adjacent particles are in phase with each other
- Adjacent particles have a different amplitude
What factors effect the first harmonic of a wave on a string?
- Tension
- Mass per unit length of the string
- Length of string
