1. TRANSVERSE & LONGITUDINAL WAVES
6.01

2. 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

3. 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

4. WAVE MOTION
How is wave motion different from the kind of motion you have studied so far?

5. 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

6. WAVE & DISTURBANCE
A wave is always associated with a disturbance

7. 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

8. MECHANICAL WAVES Require medium for propagation
Sound waves, waves in a string, water waves are mechanical waves

9. ELECTROMAGNETIC WAVES
Do not require medium for propagation
Light is an electromagnetic wave

10. 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.

11. Longitudinal Waves

12. 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

13. Sound Waves
Sound waves are longitudinal waves, similar to the waves on a Slinky:
Here, the wave is a series of compressions and stretches.

14. Sound Waves
In a sound wave, the density and pressure of the air (or other medium carrying the sound) are the quantities that oscillate.

15. Transverse Waves

16. Transverse Waves
Vibration direction perpendicular to wave propagation direction
Example: plucked string
Solids - support both longitudinal and transverse waves

17. WATER WAVES
What about water waves?

18. Water waves are a combination of transverse and longitudinal waves.

19. 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.

20. 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
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21. Graphical Representation of Waves
Displacement- time graph
Displacement – position graph

22. Parameters Distance : where along the wave are we looking
Time: at what time are we looking at the wave
Displacement : measures the disturbance

23. 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

24. 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

25. 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

26. 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.

27. Describing waves

28. 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?

29. Answer
198 wavelengths