transverse & longitudinal waves 6.01. objectives to understand the meaning of wave motion to...
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TRANSVERSE & LONGITUDINAL WAVES
6.01
OBJECTIVES
• To understand the meaning of wave motion
• To distinguish between longitudinal and transverse waves
• To define amplitude, wavelength, period and frequency and state the relationship between them
• To understand the meaning of crest and trough
OBJECTIVES ( CONTD.)
• To find amplitude and period from a displacement- time graph
• To find amplitude and wavelength from a displacement- position graph
• To use v = λf
WAVE MOTION
How is wave motion different from the kind of motion you have studied so far?
WAVE MOTION
• Wave is a way of transferring energy from one place to another without the actual large scale motion of a material body.
• Light from the Sun warms up the earth
• A soprano singing can break a crystal glass
WAVE & DISTURBANCE
• A wave is always associated with a disturbance
DEFINITION OF WAVE
• A wave is a disturbance that transfers energy from one place to another
• The direction of energy transfer is the direction of propagation of the wave
MECHANICAL WAVES
• Require medium for propagation
• Sound waves, waves in a string, water waves are mechanical waves
ELECTROMAGNETIC WAVES
• Do not require medium for propagation
• Light is an electromagnetic wave
Wave & Particle Motion
• The wave, does exhibit a net displacement in space, whereas,
• the particles of the medium exhibit only
oscillatory motion around their equilibrium positions.
Longitudinal Waves
Longitudinal Waves
• Vibration direction parallel to wave propagation direction• Particles in medium move closer together/farther apart• Example: sound waves • Gases and liquids - support only longitudinal waves
Sound Waves
Sound waves are longitudinal waves, similar to the waves on a Slinky:
Here, the wave is a series of compressions and stretches.
Sound Waves
In a sound wave, the density and pressure of the air (or other medium carrying the sound) are the quantities that oscillate.
Transverse Waves
Transverse Waves
• Vibration direction perpendicular to wave propagation direction
• Example: plucked string
Solids - support both longitudinal and transverse waves
WATER WAVES
• What about water waves?
Water waves are a combination of transverse and longitudinal waves.
Wavelength
• The length of a full wave is called the wavelength, λ , and the time needed to produce one full wave is the time period T.
Speed of the Wave
• The wave moves forward a distance equal to a wavelength in a time equal to one time period
• The speed of the wave = distance / time• v = λ / T• Number of waves produced in one second=
frequency, f• f = 1 / T• v = λ f• ..\Desktop\PhET-1.0-windows-installer.exe
Graphical Representation of Waves
• Displacement- time graph
• Displacement – position graph
Parameters
• Distance : where along the wave are we looking
• Time: at what time are we looking at the wave
• Displacement : measures the disturbance
More on displacement
• String: the height of a point on the string from the undisturbed position of the string and is measured in units of length
• Sound: the change in the density of the medium relative to the equilibrium density and is measured in units of density
• Sound: the change in the pressure of the medium relative to the equilibrium pressure
Displacement
• All waves have a displacement
• The displacement is the difference of some quantity and the equilibrium value of that quantity when no wave is present
• The displacement of any waves is a function of position( distance) and time
Crest & Troughs
• Amplitude: the maximum displacement of the wave is called amplitude
• Crest: Points on the wave with maximum positive displacement are called crests
• Troughs: Points on the wave with maximum negative displacement are called troughs
Wavelength & Period from Graphs
• The distance between successive crests/ troughs in a displacement- distance graph is the wavelength
• The distance between successive crests/ troughs in a displacement – time graph is the time period.
Describing waves
PROBLEMS
• A sound wave of frequency 450Hz is emitted from A and travels towards B, a distance of 150m away. Take the speed of sound to be 341m/s.How many wavelengths fit in the distance from A to B?
Answer
• 198 wavelengths