Chapter 4 - 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 and diffraction
What is reflection?
When wave is bounced back when it hits a boundary e.g. you can see the reflection of light in mirrors.
`What is refraction?
When wave changes direction when it enters a different medium. Change of direction is due to change of speed.
What is diffraction?
When wave spreads out as it passes through a gap or round an obstacle. e.g. you can hear sound from round a corner
What is the amplitude of a wave?
Maximum displacement from the undisturbed position. For transverse wave this is the height of a crest above equilibrium position. 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
What is the wavelength of a wave?
Length of one 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 cycle.
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 and 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?
c = frequency x wavelength
Describe experiment to measure speed of sound
- Put two microphones in a straight line a distance ,d, apart. The microphones should have different inputs so the signals 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 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 rarefractions
Give examples of longitudinal waves?
Sound waves and p 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 that oscillates in one direction (plane)
Which types 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 vibrations in line with the filter’s transmission axis can pass through the first filter.
What real world applications does polarisation have?
- Improving TV and radio signals
- sunglasses
- 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 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. This is called total destructive interference.
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 ned 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 reflected wave reinforce each other - forming a stationary waves 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 the A th 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 the resonant frequency
- The heavier (mass per unit length) the lower the resonant frequency
- lower the tension, lower the resonant frequency
State some differences between transverse and longitudinal waves
- Oscillation of particles different direction
In a stationary wave, what is the phase difference of the oscillations of particles at 2 adjacent antinodes?
180 degrees out of phase.
