Wave Properties P 11 Flashcards
(18 cards)
What are waves
Waves are repeated vibrations that transfer energy
Energy is transferred by parts of the wave knocking nearby parts
Traverse waves
Waves where the points along the length vibrate at 90 degrees to the direction of the energy transfer
For a transverse waves:
-the energy transfer is perpendicular to the wave motion
-they transfer energy, but not the particles of the medium
-they can move in solids and on the surface of liquids but not inside liquid or gases
-some transverse waves can move in solids, liquids and gases and in a vaccum
The points on wave that is:
-highest above rest position is called peak or crest
-the lowest below the rest position is called trough
Example of tranverse waves
-ripples on surface if water
-vibrations in a guitar string
-seismic waves
-electromagnetic waves
Representing tranverse waves
-transverse waves are drawn as a single continuous lone,usually with a central line showing undisturbed position
-the curve are drawn so that they are perpendicular to the direction of energy transfer
Longitudinal waves
Waves where the points along its length vibrate parallel to direction of energy transfer
For longitudinal wave:
-energy transfer is in same direction as wave motion
-transfer energy, but not the particles of medium
-can move in solid,liquid and gases
-can not move in a vaccum
Key feature:
-close together,called compressions
-space apart, rarefraction
Example of longtiduinal waves
-sound waves
- P-waves
-pressure waves caused by repeated movement ins liquid and gases
Representing longitudinal waves
Longitudinal waves are usually drawn as several line to show that the wave is moving parallel to direction of energy transfer:
-drawing lines close together represents compression
-drawing lines far apart represent rarefraction
Tranverse v longtidinal table
Traverse v longitudinal:
Structure-peak and trough, compressions and rarefraction
Vibration-90 degrees to direction of energy transfer, parallel to direction of energy transfer
Vacuum-only electromagnetic waves can travel in vacuum, cannot travel in vacuum
Material-can move in solid,liquid and gases in both
Density-constant density, changes in density
Pressure-constant pressure, changes in pressure
Speed of wave-dependent on material it is travelling in for both
Wavefronts
-both transverse and longitudinal waves can be represented as wavefronts-where waves are viewed are above
For transverse-one line represents either a peak or trough
For longitudinal-one line represents either a compression or rarefraction
-the arrow shows the direction of wave is moving and sometimes is called a ray
-the space between the lines represents the wavelength
When the lines are close together this wave is a short wavelength
When lines are far apart, this is a wave with long wavelength
Describing wave motion-amplitude
The distance from undisturbed position to peak or trough of wave
-it is given symbol A and is measure in metres
-amplitude is the maximum or minimum displacement from undisturbed position
Wavelength
The distance from one point on the wave to the dame point on next wave
-wavelength can be measured from one peak to next peak in tranverse
-wavelength can be measured from the centre of one compression to the next centre in longitudinal
-the wavelength is given symbol lambda and is measured in metres
-the distance along the wave is put on x-axis
Frequency and time period
The number of wave passing a point in each second
-given symbol f and is measured in hertz
Time period:
The time taken for a single wave to pass a point or the time taken for one full cycle of a wave
-given symbol T and is measured in seconds
f=1/T
Wave equation
The distance travelled by a wave each second
-given symbol v and is measured in m/s
-wave speed is the speed at which energy is transferred through a medium
Wave speed= frequency x length
v=f x lambda
v=m/s
f=hertz
lambda=metres
Measuring speed of waves-measuring sound between 2 points
1) 2 people stand a distance of around 100m apart
2)distance between them is measured using a trundle wheel
3)one person has 2 wooden blocks, which they bang together above their head
4)second person has a stopwatch which they start when they see the first person banging the blocks together and stops when they hear the sound
5) repeated several times and an average value is taken for the time
6)speed of sound can be calculated using equation:
Speed of sound: distance travelled by sound/time taken
Measuring the speed of waves-using ehcoes
1) a person stand 50m away from a wall using a trundle wheel to measure distance
2)the person claps 2 wooden blocks together and listen for the echo
3) the person then starts to clap the blocks together repeatedly, in rhythm of echoes
4) a second person has a stopwatch and starts timing when they hear one of the claps and stops timing 20 sec later
5)process is repeated and then average time calculated
6)distance travelled by sound between each clap and echo will be (2 x 50)m
7)the total distanced travelled by sound during 20 calps sill be (20 x 2 x 50)m
8)the speed of sound can be calculated from this distance and time using equation:
Speed of sound= 2 x distance to wall/time taken
Measuring wave speed-using an oscilliscope
1)2 microphones are connected to an oscilloscope and placed about 5m apart using a tape measure to measure distance
2)the oscilloscope is set up so that it triggers when the first microscope detects a sound, and the time base is adjusted so that the sound arriving at both microphones can be seen on the screen
3)two wooden blocks are used to make a large clap next to first microphone
4)the oscilloscope is then used to determine the time at which the clap reaches a microphone and the time difference between them
5) this is repeated several times and an average time difference calculated
6) speed can be calculated using equation:
Speed of sound= distance between microphones/time between peaks
Rarefraction
-rare fraction occurs when light passes a boundary between 2 different transparent media
-at boundary, the rays undergo a change of direction
-the direction is taken as angle from a hypothetical line called the normal-line is perpendicular to surface of boundaries and is usually represented by a straight dashed or dotted line
Change in direction depends on which media the light rays pass between:
From less dense to more dense (e.g air to glass),light bends towards normal
From more dense to less dense (e.g glass to air) light bends away from normal
When passing along the normal (perpendicular) the light does not bend at all
Wave speed and rarefraction
-the changes in direction occur due to change in speed when travelling in different substances
When light passes into a denser substance the rays will slow down, hence the bend towards the normal
-the only properties that change during rare fraction are speed and wavelength-frequency of waves does not change
Different frequencies account for different colours (red has lowest frequency,whilst blue has high frequency)
When light refracts, it does nor change colour, therefore, the frequency does not vhange
