Oscillations and Waves

Август 6, 2022

Содержание

2. Aims To know what a wave is To review previous knowledge of waves
3. What is a wave? YouTube - Water bubble in Space (zero gravity)
4. Waves Waves can transfer energy and information without a net motion of the medium through which
5. Waves Waves can transfer energy and information without a net motion of the medium through which
6. Homework Can you read pages 216 to 237 of your book before next lesson?
7. Wave fronts Wave fronts highlight the part of a wave that is moving together (in phase).
8. Rays Rays highlight the direction of energy transfer.
9. Transverse waves The oscillations are perpendicular to the direction of energy transfer. Direction of energy transfer
10. Transverse waves peak trough
11. Transverse waves Water ripples Light On a rope/slinky Earthquake
12. Longitudinal waves The oscillations are parallel to the direction of energy transfer. Direction of energy transfer
13. Longitudinal waves compression rarefraction
14. Longitudinal waves Sound Slinky Earthquake
15. Other waves - water
16. Other waves - Rayleigh
17. Displacement - x This measures the change that has taken place as a result of a
18. Amplitude - A The maximum displacement from the mean position. amplitude
19. Period - T The time taken (in seconds) for one complete oscillation. It is also the
20. Frequency - f The number of oscillations in one second. Measured in Hertz. 50 Hz =
21. Wavelength - λ The shortest distance between points that are in phase (points moving together or
22. Wave speed - v The speed at which the wave fronts pass a stationary observer. 330
23. Period and frequency Period and frequency are reciprocals of each other f = 1/T T =
24. The Wave Equation The time taken for one complete oscillation is the period T. In this
25. A water wave has a frequency of 2Hz and a wavelength of 0.3m. How fast is
26. Example A stone is thrown onto still water and creates a wave. A small cork floating
27. Example A stone is thrown onto still water and creates a wave. A small cork floating
28. Example A stone is thrown onto still water and creates a wave. A small cork floating
29. Example A stone is thrown onto still water and creates a wave. A small cork floating
30. Example A stone is thrown onto still water and creates a wave. A small cork floating
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Слайд 2

Aims
To know what a wave is
To review previous knowledge of waves

Слайд 3

What is a wave?
YouTube - Water bubble in Space (zero gravity)

Слайд 4

Waves
Waves can transfer energy and information without a net motion of

the medium through which they travel.
They involve vibrations (oscillations) of some sort.

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Waves
Waves can transfer energy and information without a net motion of

the medium through which they travel.
They involve vibrations (oscillations) of some sort.

Can you do something very boring and traditional………
Can you copy this please?

Слайд 6

Homework
Can you read pages 216 to 237 of your book before

next lesson?

Слайд 7

Wave fronts
Wave fronts highlight the part of a wave that is

moving together (in phase).

= wavefront

Ripples formed by a stone falling in water

Слайд 8

Rays
Rays highlight the direction of energy transfer.

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Transverse waves
The oscillations are perpendicular to the direction of energy transfer.
Direction

of energy transfer

oscillation

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Transverse waves
peak
trough

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Transverse waves
Water ripples
Light
On a rope/slinky
Earthquake

Слайд 12

Longitudinal waves
The oscillations are parallel to the direction of energy transfer.
Direction

of energy transfer

oscillation

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$Longitudinal waves compression rarefraction$

Longitudinal waves
compression
rarefraction

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Longitudinal waves
Sound
Slinky
Earthquake

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Other waves - water

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Other waves - Rayleigh

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Displacement - x
This measures the change that has taken place as

a result of a wave passing a particular point.
Zero displacement refers to the average position.

= displacement

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Amplitude - A
The maximum displacement from the mean position.
amplitude

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Period - T
The time taken (in seconds) for one complete oscillation.

It is also the time taken for a complete wave to pass a given point.

One complete wave

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Frequency - f
The number of oscillations in one second. Measured in

Hertz.
50 Hz = 50 vibrations/waves/oscillations in one second.

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Wavelength - λ
The shortest distance between points that are in phase

(points moving together or “in step”).

wavelength

Слайд 22

Wave speed - v
The speed at which the wave fronts pass

a stationary observer.

330 m.s-1

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Period and frequency
Period and frequency are reciprocals of each other
f =

1/T T = 1/f

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The Wave Equation
The time taken for one complete oscillation is the

period T. In this time, the wave will have moved one wavelength λ.
The speed of the wave therefore is distance/time
v = λ/T = fλ

Let’s try some questions

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A water wave has a frequency of 2Hz and a wavelength

of 0.3m. How fast is it moving?
A water wave travels through a pond with a speed of 1m/s and a frequency of 5Hz. What is the wavelength of the waves?
The speed of sound is 330m/s (in air). When Dave hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound?
Purple light has a wavelength of around 6x10-7m and a frequency of 5x1014Hz. What is the speed of purple light?

Some example wave equation questions

0.2m

0.5m

0.6m/s

3x108m/s

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Example
A stone is thrown onto still water and creates a wave.

A small cork floating 1.0 m away has the following displacement time graph (time is measured from when the stone hits the water)
a. What is the amplitude?
b. What is the speed?
c. What is the frequency?
d. What is the wavelength?

Displacement cm

Time s

-1

-2

1.4

1.5

1.6

1.7

Слайд 27

Example
A stone is thrown onto still water and creates a wave.

A small cork floating 1.0 m away has the following displacement time graph (time is measured from when the stone hits the water)
a. What is the amplitude?
2 cm

Displacement cm

Time s

-1

-2

1.4

1.5

1.6

1.7

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Example
A stone is thrown onto still water and creates a wave.

A small cork floating 1.0 m away has the following displacement time graph (time is measured from when the stone hits the water)
b. What is the speed?
= d/t = 1/1.5 = 0.67 m/s

Displacement cm

Time s

-1

-2

1.4

1.5

1.6

1.7

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Example
A stone is thrown onto still water and creates a wave.

A small cork floating 1.0 m away has the following displacement time graph (time is measured from when the stone hits the water)
c. What is the frequency?
f = 1/T = 1/0.3 = 3.33 Hz

Displacement cm

Time s

-1

-2

1.4

1.5

1.6

1.7

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Example
A stone is thrown onto still water and creates a wave.

A small cork floating 1.0 m away has the following displacement time graph (time is measured from when the stone hits the water)
d. What is the wavelength?
λ = v/f = 0.67/3.33 = 0.2 m

Displacement cm

Time s

-1

-2

1.4

1.5

1.6

1.7