Waves Flashcards
What are waves?
Oscillations of particles in a medium that transfer energy
What are progressive waves?
Waves that move - carrying energy from one place to another
What 3 things can happen to waves?
- Reflection
- Refraction
- Diffraction
What is reflection?
When a wave is bounced back when it hits a boundary
Eg. you can see the reflection of light in mirrors
What is refraction?
When a wave changes direction when it enters a different medium. Change of direction is due to change of speed
What is diffraction?
When a wave spreads out as it passes through a gap or round an obstacle
Eg. you can hear sound from round a corner
What is the amplitude of a wave?
Maximum displacement from the undisturbed position. For a transverse wave this is the height of a crest above equilibrium. Measured in metres
What is the frequency of a wave?
Number of whole wave cycles (oscillations) per second passing a given point
Measured in Hertz (Hz)
What is the wavelength of a wave?
Length of whole wave oscillation or wave cycle.
Measured in metres
What is the phase of a wave?
Measurement of the position of a certain point along a wave.
What is the phase difference?
Amount by which one wave lags behind another wave
What are phase and phase difference measured in?
Measured in angles (degrees or radians) or fractions of a cycle
What is the time period of a wave?
Time taken for one whole wave cycle
Measured in seconds
What is the equation linking frequency and time period?
frequency = 1/period
What is the equation for wave speed?
wave speed = frequency x wavelength
Describe the experiment used to measure the speed of sound
- Put two microphones in a straight line of a distance, d apart. The microphones should have different inputs so the signal from each can be recorded separately
- Use the signal generator to produce a sound from the loudspeaker and use the computer to record the time between the first and second microphone picking up the sound. (read off graph of voltage against time)
- Then use speed = distance/time
What is the speed of electromagnetic waves in a vacuum?
3.0 x 10^8 m/s
What are transverse waves?
Waves where the direction of vibration is perpendicular to the direction of energy propagation
Give examples of transverse waves
Electromagnetic Waves
Ripples of water
S waves (seismic waves)
What are longitudinal waves?
Waves where the direction of vibration of the particles is parallel to the direction of energy propagation
Consists of alternate compressions and rarefactions
Give examples of longitudinal waves
Sound waves
P waves (seismic waves)
What is superposition?
When two waves meet, the total displacement at a point is equal to the sum of the individual displacements at that point
What is a polarised wave?
A wave the oscillates in one direction (plane)
Which type of waves can be polarised?
Transverse waves - provides evidence for the nature of transverse waves
How does a polarising filter work?
Polarises unpolarised light, so that only light with oscillations in line with the filter’s transmission axis can pass through the first filter
What real world applications does polarisation have?
Sunglasses
Improving TV and radio signals
Glare reduction
How can polarisation improve TV and radio signals?
By lining up the rods on the receiving rods with the rods on the transmitting aerial - if they aren’t aligned, the signal strength will be lower
How is polarisation used in polaroid sunglasses?
Partially polarised light reflected is polarised to reduce the intensity of the light entering a person’s eye
What is constructive interference?
When two waves meet, if their displacements are in the same direction, the displacements combine to give a bigger displacement
What is destructive interference?
If a wave with positive displacement (crest) meets a wave with negative displacement (trough), they will undergo destructive interference and cancel each other out
What is total destructive interference?
If two waves with equal and opposite displacements meet, they cancel each other out
What is a stationary wave?
Superposition of two progressive waves with the same frequency (or wavelength) and amplitude, moving in opposite directions
Describe the formation of a stationary wave by setting up a driving oscillator at one end of a stretched string with the other end fixed?
Waves generated by oscillator reflect back and forth until a resonant frequency is reached where a wave and a reflective wave reinforce each other - forming a stationary wave that doesn’t move along, just vibrates up and down, with nodes and antinodes
What is a node?
Points on a stationary wave where the amplitude of the vibration is zero
What is an antinode?
Points of maximum amplitude on a stationary wave
What is the equation linking amount of wavelengths that can fit on a string and the harmonic?
at Ath harmonic, A/2 wavelengths will fit on the string
What is the first harmonic
When the stationary wave is vibrating at its lowest possible resonant frequency
How can you produce a stationary wave using microwaves?
-Reflecting a microwave beam at a metal plate - the superposition produces a stationary wave
- you can find the nodes and antinodes by moving the probe between the transmitter and reflecting plate. The meter or loudspeaker receives no signal at the nodes and maximum signal at the antinodes
Give 3 things that effect resonant frequency
Longer the string - lower resonant frequency Heavier mass per unit length - lower resonant frequency
Lower tension - lower resonant frequency
State some differences between transverse and longitudinal waves
Particles oscillate in different directions
In a stationary wave, what is the phase difference of the oscillations of particles at 2 adjacent antinodes?
180 degrees out of phase
