Waves 1 Flashcards
Define a progressive wave
A wave that transferring energy without transferring matter and made up of particles in a medium/field oscillating
Define frequency
The number of complete oscillations passing through a point per second, (measured in Hz)
Define amplitude
The waves maximum displacement from the equilibrium position, (measured in metres)
Define wavelength
The shortest distance between 2 points in phase, (measured in metres)
Define wave speed
The distance travelled by the wave per second, (units are m/s)
Define phase
The position of a certain point on a wave cycle (measured as an angle or fraction of a cycle)
Define phase difference
How much 1 particle/wave lags behind another particle/wave (measured as an angle or fraction of a cycle)
Define time period
The time taken for 1 full oscillation (measured in seconds)
Describe what it means if 2 points are in phase
- They are both at the same point of the wave cycle
- They have the same displacement and velocity
- Their phase difference will be a multiple of 2pi or 360 degrees
Describe what it means if 2 points are completely out of phase
- They are an odd number of half cycles apart ie (n+1/2) wavelengths apart
- They have the opposite displacement and velocity
- Also 1 half cycle is 180 degrees
Describe the relationship between wave speed, wavelength and frequency
wave speed = frequency x wavelength
Describe the relationship between frequency and time period
Frequency = 1/time period
Explain the difference between longitudinal and transverse waves
In longitudinal waves, the oscillations are parallel to the direction of energy transfer whereas in transverse waves, the oscillations are perpendicular to the direction of energy transfer
Describe the characteristics of EM waves
- Transverse
- travel at the same speed in a vacuum (3x10^8 m/s = speed of light)
Explain whether longitudinal waves can travel through a vacuum.
- No, they are made up of compressions and rarefactions but they require matter to compress and rarefy.
- (This means they transfer mechanical energy whereas EM waves can travel in a vacuum because they transfer light and heat energy instead)
Give 3 examples each of transverse and longitudinal waves
Transverse - EM waves, S waves and water waves
Longitudinal - Sound waves, P waves and ultrasound waves
Define a polarised wave
A wave that has been restricted to one plane
Explain why polarisation provides evidence for the nature of transverse waves
Polarisation can only occur if the waves oscillations are perpendicular to the direction of energy transfer and transverse waves oscillate in any plane perpendicular to the propagation direction whereas other waves don’t
Explain 2 examples of the uses of polarisation
- Polaroid sunglasses block glare by filtering the light to one plane
- TV and radio signals are polarised due to the orientation of the transmitting aerial. Therefore, the receiving aerial must be aligned in the same plane of polarisation to receive the signals full strength
Define superposition
When the displacements of 2 or more waves combine as they pass over each other. This can happen to all types of waves
Explain how constructive interference occurs during superposition
During superposition, constructive interference occurs at points when the 2 waves have displacement in the same direction
Explain how destructive interference occurs during superposition
During superposition, destructive interference occurs at points when 1 wave has a positive displacement and the other has a negative displacement
Explain how a stationary wave is formed
Formed from the superposition of 2 progressive waves travelling in opposite directions, with the same frequency, wavelength and similar amplitude
Explain the difference between a progressive and stationary wave in terms of amplitude
In a progressive wave, every particle has the same amplitude whereas each point on a stationary wave has a different amplitude, depending on the amount of superposition
Explain the difference between progressive and stationary waves in terms of phase difference between points
- In a progressive wave, the phase difference of points is between 0 - 360 degrees with 360 being in phase
- In a stationary wave points that have an even number of nodes between them are in phase whereas points with an odd number of nodes between them are out of phase
Explain the difference between progressive and stationary waves in terms of energy transfer
- In a progressive wave energy is transferred along the wave
- In a stationary wave, energy is stored, not transferred because there are 2 waves carrying equal energy in opposite directions
Explain the difference between progressive and stationary waves in terms of wave speed
- In a progressive wave, wave speed is the speed at which the wave moves through a medium
- In a stationary wave, each point on the wave oscillates at different speeds (max at antinodes, min at nodes) but the overall wave does not move
Explain how nodes and antinodes are formed on a stationary wave
- Nodes are formed from the destructive interference of 2 points completely out of phase, no displacement
- Antinodes are formed from the constructive interference of 2 points in phase, max displacement
Define the first harmonic
The lowest frequency at which the stationary wave can be formed
How would you calculate the wavelength of a stationary wave
Calculate the distance between 2 nodes/antinodes and double it. (Because the distance between 2 nodes/antinodes is half a wavelength)
How would you calculate the frequency of the first harmonic
f=1/2l√t/u
(√t/u is the speed of the wave and 2l is the wavelength of the first harmonic)
How would you calculate the second harmonic frequency from the first harmonic frequency
x by 2
Give 2 examples of how stationary waves can be formed in the real world
- Reflect microwaves off a metal plate, nodes and antinodes can be found using a microwave probe
- Stationary sound waves are formed using a speaker on a closed glass tube, causing the sound waves to refelct of the tube. Speed of sound can be worked out from this using c=fλ, where λ can be found knowing that the distance between nodes is half a wavelength
