SP4 Waves Flashcards
What do waves do?
- transfer energy and information
- without transferring matter
Give an example of how wavesdo not transfer matter
When buoys in sea stay still despite waves passing them
How can we describe waves?
As oscillations or vibrations around a fixed point
Define Wavelength
Distance between the same points on two consecutive waves
Define amplitude
Distance from the equilibrium line to the maximum displacement
Define frequency
the number of waves that pass a single point per second
Define period
Time taken for a whole wave to completely pass a single point
Define wavefront
The plane in which the wave travels. ie: the direction of the wave
A diagram shows a duck bobbing up and down on the surface of water as the waves pass below it. Explain how the toy duck demonstrates that waves do not transfer matter
- the plastic duck moves up and down but does not travel with the wave
- waves transfer energy but not the particles of the medium
- this means that when a wave travels between two points, no matter actually travels with it, the point on the wave just vibrate back and forth about fixed positions
- Objects floating on the water simply bob up and down when waves pass under them, demonstrating how there is no movement of matter in the direction of the wave, only energy
- can also describe the type of wave it is: eg: transverse wave
Define rest position
The undisturbed position of particles or fields when they are not vibrating
Define displacement
The distance that a certain point in the medium has moved from its rest position
**
Define peak
the highest point above the rest position
Define trough
The lowest point below the rest position
What is the symbol for amplitude and what is its unit?
- symbol: A
- unit: metres (m)
What is the symbol for wavelength and what is its unit?
- symbol: λ
- measured in metres (m)
What is the symbol for frequency and what is its unit?
- symbol: f
- unit: Hertz (Hz)
What is the symbol for time period and what is its unit?
- symbol: T
- measured in seconds (s)
What is the equation that links frequency and time period together?
f = 1/T
What is the equation for wave speed?
frequency x wavelength
What is the relationship between frequency and velocity?
As frequency increases, velocity increases
What is the relationship between wavelength and velocity?
As wavelength increases, so does velocity
What is the relationship between period and frequency?
- period is inversely proportional to frequency
- so as period increases, frequency decreases, and vice versa
What is the relationship between period, frequency and velocity?
period decreases, frequency + velocity increase
Define longitudinal waves
vibrations are parallel to the direction of travel
What are the key features of a longitudinal wave and what are their definitions?
- compressions: points of high pressure because particles are close togther
- rarefactions: points of low pressure because particles are spaced far apart
What mediums can longitudinal waves travel through?
- solids
- liquids
- gases
- not a vacuum
What are some examples of longitudinal waves?
- sound waves
- seismic P waves
- pressure waves caused by repeated movements in liquids and gases
Define transverse waves
Vibrations are perpendicular to the direction of travel
What mediums can transverse waves travel through?
- solids
- surfaces of liquids
- not inside liquids or gas
What mediums can electromagnetic transverse waves travel through?
- solids
- liquids
- gases
- vacuum
What are some examples of transverse waves?
- seismic s waves
- electromagnetic waves
- ripples on the surface of water
How do we measure the speed of sound in air?
Method 1: Make a noise ~50 m away from a wall and record the time for the echo to be heard. Then substitute the values into s=d/t
Method 2: Have two microphones connected to a datalogger at a large distance apart, and record the time difference between the sound passing from one to another - then use the equation s=d/t
How do we measure the velocity of ripples of water on its surface?
- Choose a calm flat water surface such as a lake or a swimming pool
- Two people stand a few metres apart using a tape measure to measure this distance
- One person counts down from three and then disturbs the water surface (using their hand, for example) to create a ripple
- The second person then starts a stopwatch to time how long it takes for the first ripple to get to them
- The experiment is then repeated 10 times and an average value for the time is calculated
- The average time and distance can then be used to calculate the wave speed using the equation: s=d/t