P5 Flashcards
What are waves?
-a wave is an oscillation that transfers energy
Examples of a wave (the microphone in a phone and electromagnetic waves):
-The microphone in your phone produces a signal that varies in the same way
-electromagnetic waves are used to communicate between the two phones
What is special about sound and water waves?
Sound and water are mechanical waves so they need medium (matter) to travel through
-this is not the case for non-mechanical waves like electromagnetic waves
What kind of waves are sound waves?
Sound waves are longitudal
-the direction of vibration of individual air molecules is the same as the direction of the wave
What happens in transverse waves?
In transverse waves the direction of vibration is at right angles to the direction of travel of the wave.
-if you make a transverse wave on a spring the individual coils move up and down but the energy is transferred horizontally.
What is amplitude?
Amplitude is the distance from the middle to the top(crest) or bottom (trough) of the wave
What is the symbol for amplitude?
A
What is the unit of amplitude?
Depends on the wave
E.g metres or volts
What is wavelength?
Distance from one point on a wave to the same point in the next wave
What is the symbol for wavelength?
Lambda
What is wavelength measured in?
Metres, m
What is the frequency of a wave?
The number of waves, or oscillations per second.
What is the frequency of a wave measured in?
Hertz, Hz
What is the symbol for frequency?
F
What is the time period (waves) ?
The time for one wave to pass a given point
What is the symbol for time period?
T
What is the unit for time period?
Seconds /s
What are the two ways to represent a wave?
A time trace and a snapshot
What does a time trace do?
Shows how the displacement varies with time at a particular position.
What does a snapshot representation do?
A snapshot of a wave shows how displacement varies with distance at a particular time
Do waves have velocity?
Yes
How do you model waves?
You have learned that you can model electric circuits with ropes and field lines with rubber bands
-another important model is using ripples on water to model transverse waves
-for example you can show how waves are reflected
-in a ripple you can see how the surface of the wave moves up and down as the wave moves through the water
-you can see that by putting a small cork on the surface, the wave travels but the water does not
-this is the same for sound waves, the wave moves away from your mouth but the air does not
Calculating wave velocity example:
Imagine running along a track. Your stride is 1.5metres long and you take 2 strides each second
-from this information you could calculate that you gave travelled 3m/s
In terms of waves your stride represents the wavelength and the “strides per second” represent the frequency
So wavelength x frequency = velocity of wave
Equation for calculating wave velocity:
Wave velocity (m/s) = frequency (Hz) x wavelength (m)
What is the unit of frequency in terms of waves?
The unit of frequency is the unit of number of waves per second
There is no unit for number of waves so
1Hz = 1/s
How do you measure the velocity of ripples?
-if you use a ripple tank, you need to know the frequency of the ripples and their wavelength, to calculate velocity.
You can find the wavelength using a flashing light (a strobe) and a ruler, and the frequency by finding the number of rotations of the motor per second.
Then you can use the equation to calculate the velocity of the waves.
How do you measure the velocity of sound?
If you time how long it takes to hear an echo (reflection) of a clap when you are at a distance from a wall you can work out the velocity of sound using the equation that links distance velocity and time.
What’s another way you can measure the velocity of sound?
Alternatively, you can connect a pair of microphones a certain distance apart from an Oscilloscope.
-you can use the method with the microphones to measure the velocity of sound in a liquid or a solid.
-remember that sound is a longitudal wave so when you see the trace of a transverse wave in the screen of an oscilloscope it is showing the variation of pressure with time, not the sound wave itself
-the velocity of sound can vary with temperature and pressure. This is because these factors affect the velocity at which the disturbance in the wave is transferred between particles.
What is refraction?
When a wave travels from one medium to another it’s velocity can change and so can it’s direction(refraction)
