1. GENERAL PROPERTIES OF WAVES
INTRODUCTION TO WAVES
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2. Tsunami
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3. Uses of waves
What are some examples or applications of waves in everyday life?
Hydropower
Guitar/piano, in fact all musical instruments
The above are mechanical waves
Some electromagnetic waves includes light, radio waves, x-rays
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4. Kallang Waves!
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5. What is a wave? Spreading of disturbance from one place to another.
The source is a vibration or oscillation.
Energy is transferred from one point to another WITHOUT physical transfer of any material between the two points
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6. Demo WAVES Slinky or ropes Transverse waves
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7. Transverse Waves
Transverse waves travel in a direction PERPENDICULAR to the direction of the vibrations.
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9. Transverse Waves Some Examples: water waves rope waves
electromagnetic waves (example: light)
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10. The Slinky Coil
What do you notice about the direction of the vibrations and the direction of the wave?
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11. The other type of wave called…
… Longitudinal Wave…
What is a longitudinal wave?
A wave where the direction of travel is parallel to the direction of vibration.
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12. How does it look like? Demonstration of a longitudinal wave?
Slinky Coil
On an Applet
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13. Longitudinal Waves Compression Rarefaction
Places where air pressure is slightly higher than the surrounding air pressure.
Rarefaction
Places where air pressure is slightly lower than the surrounding air pressure.
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14. Longitudinal Waves
Examples
- Sound waves
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15. LONGITUDINAL WAVES
Longitudinal waves travel in a direction PARALLEL to the direction of vibrations.
We use compressions and rarefactions to describe them
Compression
Rarefactions
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16. Demo on applet http://www.ngsir.netfirms.com/englishhtm/Lwave.htm
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17. Example Q.
A sound wave in air has a frequency of 262Hz and travels with a speed of 343m/s.
How far apart are the wave compressions? A.
Given f = 262 Hz and v = 343m/s,
Distance between wave compression
= wavelength = v / f = 1.3m (1 dp)
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18. Wavefront
That is a…
wavefront - an imaginary line on a wave that joins all points which have the same phase of vibration.
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19. Crests and Troughs Crests: points of maximum displacement on a wave
Troughs: points of minimum displacement on a wave
displacement
CREST
Distance
along rope
TROUGH
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20. AMPLITUDE (A) Maximum Displacement from the rest or central position.
SI unit metre (m)
displacement
crest
crest
amplitude
distance along rope
amplitude
trough
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21. Wavelength (λ)
The distance between two successive points of the same phase. Example: distance between two crests. SI unit: metre (m).
displacement
Wavelength
crest λ
crest
amplitude
position along rope
amplitude
trough
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22. Frequency (f)
Number of complete waves generated per second (or number of cycles/oscillations per second)
SI unit: hertz (Hz)
E.g: 5 Hz mean 5 waves generated in 1s
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23. Period (T)
Time taken to generate one complete wave (or to complete one cycle)
SI unit: second (s)
E.g.
5 Hz mean 5 waves generated in 1s
1 wave is generated in 1/5 = 0.25 s
Therefore, Period (T) = 0.25s
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24. Relationship between T and f
As f increases, T decreases
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25. How fast is the wave moving?
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26. Find the velocity of waves
Velocity of wave is the product of its frequency and wavelength
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27. Example Q.
A fisherman notices that wave crests pass the bow of his anchored boat every 3.0s.
He measures the distance between two successive crests to be 6.5m.
How fast are the waves travelling? A.
From the question, we know the period, T = 3.0s, and the wavelength is 6.5m.
Therefore, wave speed, v = 6.5 / 3 = 2.2ms-1 (1 dp)
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28. Using the 2 formulas, can you combine them and formed a third equation?
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29. 2 types of graphs to note! The displacement-position graph
Able to find wavelength
Amplitude
The displacement-graph
Period
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30. Displacement-time graph
Distance between two crests denotes the period in a displacement-time graph.( Contrast this with the displacement-position graph! What is the difference?)
displacement
Period
crest T
crest
amplitude
time
amplitude
trough
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31. Displacement-time and displacement-position graphs
Displacement-time graph：
Shows the displacement of ONE particle (from the rest position) at different times.
ONE
at different times
Displacement-position graph：
Shows the displacement of ALL particles at a certain time.
ALL
at a certain time
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32. Try this
Textbook page 177
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33. Question Particles in the medium vibrate when the wave passes by.
In which direction does the particle move?
motion of wave
wave at
next moment ? ?
wave at
this moment
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34. Question In which direction does particle a move? ? ? motion of wave
wave at
this moment ?
wave at
next moment
Downwards.
To the right.
Other： _______
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35. Vibration vs Waves
Vibrations simply refers to one single particle vibrating at its mean position
Waves refer to the all the particles’ vibrations with respect to time
They are essentially different! Don’t mix these two terms up.
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36. SUMMARY
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