Section 3: Waves Flashcards
What are waves?
Just vibrations. They transfer energy through a medium, but once they’ve gone through everything goes back to normal like they where never there.
What is a progressive wave?
A moving wave. It carries energy from one place to another without transferring any material.
What is a wave caused by?
It is caused by something making particles or fields (e.g. Electric or magnetic fields) oscillate at a source. These oscillations pass through the medium as the wave travels, carrying energy with it. A wave transfers this energy away from the source so the source of the wave loses energy.
What ways can you tell that waves carry energy?
- electromagnetic waves cause things to heat up
- x-rays and gamma rays knock electrons out of their orbits, causing ionisation
- loud sounds cause large oscillations of air particles which can make things vibrate
- wave power can be used to generate electricity
- waves can be reflected, refracted and diffracted
What is reflection?
The wave is bounced back when it hits a boundary
What is refraction?
The wave changes direction as it enters a different medium. The change in direction is a result of the wave slowing down or speeding up.
What is diffraction?
The wave it spreads out as it passes through a gap or round an obstacle
What is displacement and what is it measured in?
How far a point on the wave has moved from its undisturbed position.
Measured in meters
What is Amplitude and what is it measured in?
The maximum magnitude of the displacement, i.e. the distance from the undisturbed position to crest, or trough.
Measured in meters
What is wavelength and what is it measured in?
The length of one whole wave oscillation or wave cycle, i.e. The distance between two crests of a wave
Measured in meters
What is period and what is it measured in?
The time taken for one whole wave cycle
Measured in seconds
What is frequency and what is it measured in?
The number of whole wave cycles (oscillations) per second passing a given point. Or the number of whole wave cycles (oscillations) given out from a source per second
Measured in hertz
What is phase?
A measurement of the position of a certain point along the wave cycle.
What is phase difference?
The amount by which one wave lags behind another wave. It can be measured in angles or in fractions of a cycle
How are frequency and period linked together?
The number of whole wave cycles (oscillations) per second is 1/(time taken for one oscillation)
What is the equation for working out frequency?
F = 1/T
Frequency (Hz) = 1 / time in seconds
How can you find the speed of a wave?
You can you speed = distance / time
C = d / t
C = f x lambda
What’s speed do all electromagnetic waves travel through a vacuum?
3.00 x 10^8 ms^-1
How can you measure the speed of sound?
One of the easiest methods is to use two microphones in a straight line a distance D apart. The microphones should have separate inputs so the signals from each can be recorded separately. use a 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. Do this by measuring the time delay between the first peak of the signal received by each microphone on a graph of voltage against time.
How can you measure the speed of a wave in water?
- set up a ripple tank
- record the depth of the water
- create ripples with a regular frequency
- dim main lights of the room and use a strobe light
- increase the frequency of the strobe light until the waves appear to be standing still. When this happens the frequency of the strobe light equals the frequency of the water waves.
- Use a ruler to measure the distance between two adjacent peaks.
What are the two different types of waves?
Transverse and longitudinal
What is a transverse wave?
In transverse waves the displacement of the particles or field is at right angles to the direction of energy propagation. All electromagnetic waves are transverse. They travel as vibrations through magnetic and electric fields - with vibrations perpendicular to the direction of energy transfer.
What are the two main ways of drawing transverse waves?
They can be shown as graphs of displacement against distance along the path of the wave. Or they can be shown as graphs of displacement against time for a point as the wave passes. Both of the graphs give a similar shape, so make sure you check the label on the x-axis.
What is a longitudinal wave?
In longitudinal waves the displacement of the particles or Fields is along the direction of energy propagation. The most common example is sound.