Oscillations and Waves

1. Topic 4 Oscillations and Waves

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 they travel.
They involve vibrations (oscillations) of
some sort.

5. 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?

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).
= wavefront
Ripples formed by a
stone falling in water

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
oscillation

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
oscillation

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

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 time taken for a
complete wave to pass a given point.
One complete wave

20. Frequency - f

The number of oscillations in one second.
Measured in Hertz.
50 Hz = 50 vibrations/waves/oscillations in one second.

21. Wavelength - λ

The shortest distance between points that
are in phase (points moving together or “in
step”).
wavelength

22. Wave speed - v

The speed at which the wave fronts pass a
stationary observer.
330 m.s-1

23. Period and frequency

Period and frequency are reciprocals of
each other
f = 1/T
T = 1/f

24. 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

25. Some example wave equation questions

1) A water wave has a frequency of 2Hz and a wavelength
of 0.3m. How fast is it moving?
0.6m/s
2) 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?
0.2m
3) 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?
0.5m
4) Purple light has a wavelength of around 6x10-7m and a
frequency of 5x1014Hz. What is the speed of purple
light?
3x108m/s

26. 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)
Displacement cm
a. What is the amplitude?
b. What is the speed?
c. What is the frequency?
d. What is the wavelength?
1
1.4
-1
-2
1.5
1.6
1.7
Time s

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)
Displacement cm
a. What is the amplitude?
2 cm
1
1.4
-1
-2
1.5
1.6
1.7
Time s

28. 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)
Displacement cm
b. What is the speed?
= d/t = 1/1.5 = 0.67 m/s
1
1.4
-1
-2
1.5
1.6
1.7
Time s

29. 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)
Displacement cm
c. What is the frequency?
f = 1/T = 1/0.3 = 3.33 Hz
1
1.4
-1
-2
1.5
1.6
1.7
Time s

30. 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)
Displacement cm
d. What is the wavelength?
λ = v/f = 0.67/3.33 = 0.2 m
1
1.4
-1
-2
1.5
1.6
1.7
Time s

31. Let’s try some questions!

Page 225 Questions 3, 4
Page 226 Questions 7, 8,11
Page 227 Question 15, 17