IGCSE Wave physics notes (updated)
Content
13.1 Describing wave motion 13.2 Wave terms
13.3 Wave behaviour
Learning outcomes
Candidates should be able to:
- (a) describe what is meant by wave motion as illustrated by vibrations in ropes and springs and by
experiments using a ripple tank. - (b) state what is meant by the term wavefront.
- © define the terms speed, frequency, wavelength and amplitude and recall and use the formula velocity = frequency × wavelength.
- (d) describe transverse and longitudinal waves in such a way as to illustrate the differences between them.
- (e) describe the use of a ripple tank to show
(1) reflection at a plane surface,
(2) refraction due to a change of speed at constant frequency.
(f) describe simple experiments to show the reflection of sound waves.
Sound/Longitudinal Waves:
Content
Learning outcomes
Candidates should be able to:
- (a) describe the production of sound by vibrating sources.
- (b) describe the longitudinal nature of sound waves and describe compression and rarefaction.
- © state the approximate range of audible frequencies for the healthy human ear as 20Hz to 20000Hz.
- (d) explain why a medium is required in order to transmit sound waves and describe an experiment to demonstrate this.
- (e) describe a direct method for the determination of the speed of sound in air and make the necessary calculation.
- (f) state the order of magnitude of the speeds of sound in air, liquids and solids.
- (g) explain how the loudness and pitch of sound waves relate to amplitude and frequency.
- (h) describe how the reflection of sound may produce an echo.
- (i) describe how the shape of a sound wave as demonstrated by an oscilloscope is affected by the quality (timbre) of the sound wave.
- (j) define ultrasound.
(k) describe the uses of ultrasound in cleaning, quality control and pre-natal scanning.
Notes For Transverse Waves :
- What is Meant By Wave Motion :
- Wave motion is the movement and progress of Waves which is the change in state from rest to equilibrium.It can also be defined as the propagation of a wave.Therefore a wave is a disturbance that transfers energy from one point to another which is formed by energy transfer.
- Illustrating Wave Motion Through ropes:
From the above picture , where the rope is joined at the one end from tree and is disturbed on the other end by a person , disturbance in medium is created and a wave is formed.The Kinetic Energy from the moving hand is transferred to rope particles which move up and down.In this wave progresses until it reaches the tree.It is to note that the wave direction is perpendicular to the particle vibration direction which is a major property of transverse waves.
- Illustrating Wave Motion Through Ripple Tank :
From the above image it can be viewed that that with the help of oscillating paddle , disturbances are created in tank , hence wave is produced.When the wave progresses along the ripple tank , the water particles move up and down (showing transverse wave).It is to note that the waves which are produced are only in circular motion but still are perpendicular to the up and down moving water particles.The table shows the moving waves (shadow).
- Illustrating Waves with Slinky Spring :
The wave demonstration is spring is very similar to that of rope.It is to note that springs can produce both transverse and longitudinal waves , but here we are only viewing transverse case.When spring is moved from left to right or vice versa , the transverse waves progress through the spring which can be proved as the waves form a 90 degree angle with particles.
What is a Wave Front :
A wave front is a imaginary line on a wave that connects all adjacent points in phase.It can be drawn by joining all adjacent waves crests in phase of different waves.The wave fronts can be straight lines , concentric centres and other shapes.
The surface can also be said to be the locus of points that have the same phase.The wavefront is perpendicular to the ray that represents an electromagnetic waves (EM). The plane in which the electric and magnetic field vectors lie is tangential to the wavefront at each and every point.
Important Terms:
Speed:
The wave speed is the distance travelled by wave per second , it is derived from the formula , Speed = Distance / Time .
Frequency:
The frequency of a wave is the number of complete waves produced in one second.The SI units of frequency are Hertz.It can also be described as number of crests or trough that go through a point per second. Frequency and time period are inversely proportional (when one increases other decreases) and higher the frequency , the greater the waves.
Wavelength:
Wavelength is the distance between identical points in the adjacent cycles of a wave produced.The identical points may be two consecutive crests or troughs.
Amplitude:
The maximum vertical displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position.
Cambridge students should also know :
Wave Speed = Frequency * Wavelength
(v = f*w) where f = frequency and w = wavelength
Differences between transverse and longitudinal waves:
- A longitudinal wave is a wave where the movement of the medium is in the exact direction as the wave. On the other hand, a transverse wave is a wave where the movement of the medium is at a perpendicular to the wave direction.
- Examples of longitudinal waves include: Sound waves in air, waves formed a long a compressed spring and seismic waves whereas example of transverse waves include water waves.
- Longitudinal waves cause changes in the pressure of the different parts of the medium through which they go through. On the other hand, transverse wave do not cause pressure changes in the medium through which they move.
- Longitudinal waves can be transmitted through all the three types of media, that are solids, liquids and gases.Apart transverse waves can only be transmitted through solids or over liquid surfaces.
- Longitudinal waves travel in the form of alternate compressions and rarefactions whereas transverse waves can be transmitted in the form of crest and toughs.
- Speed of longitudinal waves is comparatively less that that of transversely moving waves.
Cambridge also requires its candidates to illustrate reflection and refraction of sound :
By placing a metal bar in the tank and tapping/clicking the wooden bar a pulse of three of four ripples can be forwarded towards the metal bar. The ripples reflect through the bar. If the bar is placed at an angle to the wavefront the reflected waves can be observed to obey the law of reflection. The angle of incidence and angle of reflection will be equal.
If a sheet of glass is placed in the tank, the depth of water in the tank will be shallower over the glass and other deep region would form. The speed of a wave in water depends on the depth, so the ripples slow down as they pass over the glass, means they move from deep to shallow. This causes the wavelength to decrease as well.
Sound:
How Sound Is Produced:
Sound is formed due to disturbance in a medium , like the transverse waves.However the disturbance is caused by vibrations in either solid , liquid or gas.The vibration causes waves to form which are longitudinal waves as the medium around vibrations itself vibrate.The wave direction during this case is parallel to particle vibration direction , such as in a guitar or tuning fork.
Sound Waves are longitudinal in nature primarily due to their parallel particle vibration to wave direction and a series of compression and rarefaction;
Compression And Rarefaction For Sound:
Sound waves progress and are produced due to series of compression and rarefactions.During the compression , the pressure increases due to closely packed particles and during rarefaction the pressure decreases as particles are spaced away as compared to those of compression.The diagram below explains the scenario :
AND:
Now when you know about the basics that sound is form of longitudinal wave , you should know that the audible human frequency is between 20 Hertz to 20,000 Hertz.Any sound above or below this range cannot be heard by humans.With growing age , this limit even narrows.
Why Sound needs a medium and cannot propagate through vacuum?
Sound needs a medium for their propagation like solid, liquid or gas to travel because the molecules of solid, liquid and gases carry sound waves from one place to another. Sound cannot progress through the vacuum because the vacuum has no molecules thus sound cannot progress.It is to note that sound travels fastest in solids followed by liquid and then gas.
Experiment to show that sound needs a medium to travel:
In the above case pump the air out of jar , then allow the sticker to strike the bell.After striking, the bell could be viewed moving but one cannot hear the sound.However if air is pumped back and the experiment is repeated , then one hears sound as well.
Experiment to show speed of sound:
Place two people exactly 1000 meters apart with one man a gun and other with the stopwatch.When the man shoots with the gun and other person watches the gun powder , let him start the stopwatch and stop when he hears the sound.Repeat the experiment to reduce human error.Then divide 1000 (distance) with the time on stopwatch to get speed as
Speed = Distance/time
Relating loudness and pitch with amplitude and frequency:
The loudness is directly related to the amplitude.The higher the amplitude , the higher the loudness of sound.
Likewise pitch is a property of sound , that is related to the frequency.These both are also directly related as when higher the frequency of the sound , the higher the pitch.For example the pitch of sound of 200Hz is lower than that of 400Hz.
It is also really important to know the pitch production with the length of tuning fork . You should always remember that that the tuning fork with long prongs produce a sound with lower frequency than the tuning fork with shorter prongs.This is because tuning fork with longer prongs produce sound with long wavelength , hence with low frequency , therefore low pitch and vice versus with that of shorter prongs .
All You Should Know About Echo For your CIE:
Echo is the repetition of sound due to the reflection/bouncing back of sound due to contact with a surface. A echo is formed when a sound hits a surface and reflects back at the same angle which it produced when it strikes the surface or in easy words its angle with the normal
Angle of Incidence = Angle Of Reflection (only for reflection of sound / echo in this case)
OR
Lastly you should only only that the the echo is used for echolocation and for measuring large distances.
A timbre is the quality of a sound and is affected through various factors.It is affected by factors such as wavelength m speed and frequency . A CRO (cathode ray oscilloscope) displays the sound waves in the form of waves which is like
Finally you should also have a knowledge about ultrasound and its uses.Ultrasound are sound waves with frequency higher than 20,000Hz that is the upper limit of audible human hearing range!
USES:
Ultrasonic cleaning uses cavitation bubbles induced by high frequency pressure (sound) waves to agitate a liquid.
It is also used for insuring food quality by penetrating the rays into food substances.
Lastly it is also used for prenatal scan as it rays are not at all harmful to the women.
Originally published at https://root469.blogspot.com/2019/11/o-level-physics-transverse-and.html
