1. Waves

2. What is a wave?
Conduction and convection are both processes that transfer energy (thermal in this case) using particles…

3. What is a wave?
However, in space, there are no particles. Therefore, there must be a different way for the heat from the sun to reach us. This happens because of waves.

4. What is a wave?
Waves transfer energy from one place to another. This means that energy can be transferred without particles.

5. Longitudinal waves
Longitudinal waves have oscillations parallel (in the same direction) to the direction of motion
Longitudinal waves show areas of compression and rarefaction.
Examples of longitudinal waves are sound and the primary waves produced by an earthquake

6. Transverse waves
Transverse waves have oscillations perpendicular (at 90°) to the direction of motion
Examples of transverse waves are light, water waves and the secondary waves produced by an Earthquake.

7. Modelling waves
The wave travels away from the source. The direction of the wave is at right angles to the movement of the source.
In a transverse wave, the coils do not travel horizontally, each coil of the Slinky just vibrates up and down.
coils vibrate
up and down
source moves
up and down
direction of wave

8. Modelling waves
The wave travels away from the source. The direction of the wave is parallel to the movement of the source.
In a longitudinal wave, the coils do not travel horizontally, each coil of the Slinky just vibrates left and right.
coils vibrate
left and right
source moves
left and right
direction of wave

9. Mini-Plenary
Copy down the true sentences and change the false sentences to make them true.
Longitudinal waves have oscillations parallel to the direction of motion
Transverse waves show areas of compressions and rarefaction
Sound waves are examples of longitudinal waves
Waves require particles to transfer energy
Water waves and secondary earthquake waves are examples of transverse waves

10. Wave terminology
Draw the example wave in your book and try and label the amplitude and wavelength.

11. Wave terminology
There are certain definitions regarding waves that you are required to know:
Wavelength – the distance from peak to peak/trough to trough on a wave
Frequency – the number of waves per second. This is measured in hertz (Hz)
Amplitude – The height of a wave above the zero line

12. Match the term to the correct definition
Mini-Plenary
Match the term to the correct definition
Waves
Wavelength
Frequency
Amplitude
The height of a wave above the zero line
They transfer energy from one place to another without the need for particles
The number of waves per second
The distance from peak to peak/trough to trough on a wave

13. Calculating Waves Is this a longitudinal or transverse wave?
Fill in the two boxes on the diagram
Give an example of waves which travel in this way?
Longitudinal
Rarefaction
Compression
Sound, “P” waves, Shock waves, Ultrasound
Complete the following sentence:
On the moon astronauts have to use radios to communicate because…
sound is a longitudinal wave and needs a medium to travel.
Name 3 types of transverse wave:
Light Infrared
Radio Ocean
Microwave Gamma Ray
“S” waves X-ray
Ultra Violet

14.  a  a  Calculating Waves
Peak ? 
Time a ?
Trough 
a = amplitude, this is half the height of the wave.
The higher the amplitude the greater the energy.
 = wavelength, this is the distance between one wave and the next.

15. Calculating Waves f = the number of waves to pass a point every second
Copy and complete:
f = the number of waves to pass a point every second
f = ___________.
f is measured in _________.
f can be calculated using the equation _____________ /_______
Therefore 1 wave per second = 1 __________.
frequency
Hertz (Hz)
number of waves
time
Hertz (Hz)
Wave
Cycles
Time (s)
Frequency (Hz) 6 2 10 1 3 5
0.5

16. Calculating Waves
Imagine waves on the sea travelling over a shipwreck:
 = 2m
1 second later:

17. v x f Calculating Waves 
In the diagram, 5 waves pass the shipwreck in 1 second therefore the frequency = 5 Hz
From the diagram we can see the wavelength () = 2m
This means that the waves travel 10m in 1s so the speed is 10m/s
To recap:
frequency (f) x wavelength () = speed (V)
5Hz x 2m = 10m/s

18. Calculating Waves  (m)
Copy the table and fill in the missing sections:
Wave
f (Hz)
 (m)
v (m/s)
Water Wave 2
1.5
Mexican Wave 40 8
Musical Note
256
338
Rope 3
0.8
Ultrasound
35,000
350
3.0
0.2
1.32
2.4
0.01
A wave travelling on a string has a wavelength of 0.10 m and a frequency of
7 Hz.  
Calculate the speed of the wave:
7 Hz x 0.10 m = 0.7 m/s

19. Calculating Waves
A water wave is moving across the surface of a lake. The wave has a wavelength of 2 m and a frequency of 2.5 Hz.
Calculate the speed of the wave:
2.5 Hz x 2 m = 5 m/s
A sound wave is moving through air. The wave has a wavelength of 0.65 m and a frequency of 512 Hz.
512 Hz x 0.65 m = m/s
A wave has a wavelength of 6m and a frequency of 5 Hz.
5 Hz x 6 m = 30 m/s
A ripple travels across the surface of a pond at 0.03 m/s, it has a wavelength of 0.15 m.
Calculate the frequency of the wave:
0.03 m/s / 0.15 m = 0.2 Hz

20. Calculating Waves 
Frequency (Hz)
Wavelength (cm)
Wavelength (m)
Wave speed (m/s) 10
0.1
2.5 30 2 50 1 1
0.1
0.25
0.02
0.6
0.5
0.01
Wave length (m) = Wave Speed (m/s) / Frequency (Hz)
 = v / f
Wave speed (m/s)
Frequency (Hz)
Wavelength (m)
0.6 24 30 12 20
0.025
0.02
0.05
0.03

21. Calculating Waves
 Frequency (Hz) = Wave Speed (m/s) / Wave Length (m)
f= v / 
Wave speed (m/s)
Wavelength (m)
Frequency (Hz)
1.5
0.75
1.2
0.4 4
0.5 3
0.3 2 3 8 10

22. Reflection

23. the bouncing of a wave off a surface
Reflection
the bouncing of a wave off a surface
Barrier

24. a wave that strikes an object
Incident wave
a wave that
strikes an
object
Barrier

25. a wave that strikes an object Normal
Incident wave
a wave that
strikes an
object
Normal
a line perpendicular to a surface
Barrier

26. a wave that strikes an object Normal Reflected wave
Incident wave
a wave that
strikes an
object
Normal
a line perpendicular to a surface
Reflected wave
a wave that bounces off
a surface
Barrier

27. Law of Reflection is equal to the angle of reflection
the angle of incidence
is equal to the angle
of reflection
Angle of
incidence
Angle of
reflection
Barrier
Objects bounce off of surfaces at
the same angle at which they hit them.

29. Refraction

30. Refraction
Waves are refracted when they change speed e.g. when they travel from deep (fast) to shallow (slow) water.
When this happens:
Wavelength gets shorter
They change direction
Wavelength λ
Wavelength λ

31. Do the waves speed up or slow down as they move from the air to water?
Watch the simulation in this link for two minutes, then answer the following questions...
Do the waves speed up or slow down as they move from the air to water?
Do the waves change direction and what is this called?
Where do the waves change direction?
What can you say about the wavelength of the waves?
Is some of the wave energy reflected as well as refracted?
They slow down as they move from the air to the water.
Yes, the waves do change direction. This is called refraction.
The waves change direction at the boundary. Then they travel in straight lines.
The wavelength is shorter in the water.
Yes, some of the wave energy reflects (bounces) off the boundary as well as being refracted (changing direction at the boundary.)

32. Place the block in the middle of a sheet of A4 paper.
Draw an outline around it

33. Place the block in the middle of a sheet of A4 paper.
Draw an outline around it
Take the block away
Find the middle of the straight edge
Draw a 90º line through this point – this is the normal line
The NORMAL Line

34. Direct a laser beam as shown
Put the block back
Direct a laser beam as shown
To Answer:
Is the beam crossing from glass to air or air to glass?
Is the beam bent away from or towards the normal?
Is this because it’s slowing down or speeding up?
The NORMAL Line

35. Sand (slow)
Concrete (fast)

36. Sand (slow)
Concrete (fast)

37. Sand (slow)
Concrete (fast)

38. Back to start
Sand (slow)
Concrete (fast)
When waves cross from fast to slow, they are refracted towards the normal.

39. Direct a laser beam as shown
To Answer:
Is the beam crossing from glass to air or air to glass?
Is the beam bent away from or towards the normal?
Is this because it’s slowing down or speeding up?
The NORMAL Line

40. Sand (slow)
Concrete (fast)

41. Sand (slow)
Concrete (fast)

42. Sand (slow)
Concrete (fast)

43. Back to start
Sand (slow)
Concrete (fast)
When waves cross from slow to fast, they are refracted away from the normal.

44. Note if there is a reflected ray present as well
Gradually make the angle of incidence larger until the angle of refraction is 90º
Note if there is a reflected ray present as well i r
The NORMAL Line

45. This is called the critical angle.
Refraction does not happen after this point.
After this, the light is TOTALLY INTERNALLY REFLECTED (T.I.R.ed) c
The NORMAL Line

46. The reflected angle r is always equal to the incident angle i.
The beam is T.I.R.ed* when the incident angle i is larger than the critical angle c.
The reflected angle r is always equal to the incident angle i.
* T.I.R.ed = totally internally reflected i r
The NORMAL Line

47. Summary Copy the 2nd para and 3 diagrams on p.158 c Air into glass
Light bent towards the normal
Light slows down
Glass into Air
Light bent away from the normal
Light speeds up
Critical Angle
Light is refracted at 90º
This is the last angle at which refraction happens. (T.I.R. after this.)
T.I.R.
Total Internal Reflection

48. Optical Fibres
is guided by T.I.R
and comes out here.
Light in at this end . . .
Optical fibres are used in communications to carry signals. (The signals are pulses of laser light)
Optical fibres are used in medicine to look inside the body. An endoscope is made of a bunch of optical fibres to carry light into and out of the body.

49. Diffraction

50. Diffraction
Diffraction occurs when a wave passes through a gap that is the same size or smaller than the wavelength of the wave.
When diffraction occurs, the wave becomes curved as it passes through the gap.

51. Diffraction in everyday life
The waves are being diffracted as they enter the coves as the size of the opening is smaller than the wavelength of the waves

52. Diffraction in everyday life
These barriers reduce noise from motorways. However, the gaps between the barriers must be carefully controlled to stop the noise from diffracting and spreading further.

53. Diffraction in everyday life
In some areas, houses are hidden behind large hills. This means that radio and TV signals are blocked and diffracted. Taller buildings are able to receive the diffracted signals, but smaller homes are not!

54. What are the properties of reflection, refraction and diffraction?
Task: Copy and fill out the table below (12m)
Definition
Properties
Examples
Reflection
e.g. the law of reflection states that …
Refraction
The change in _________ of ________ when they travel across a b_______
S_______ pool appearing s_______than it is
Diffraction
The n_______ a gap is, the g_________ the diffraction
The w_______ a gap is, the _________ the diffraction
*if extra speedy: we do not normally see diffraction of light in everyday life. Explain why.

55. What are the properties of reflection, refraction and diffraction?
Definition
Properties
Examples
Reflection
The change in direction of a wave, such as a light or sound wave, away from a boundary the wave encounters
e.g. the law of reflection states that the angle of incidence = the angle of reflection
occurs when light changes direction as a result of "bouncing off" a surface like a mirror
Mirrors
e.g. mirror sign in an ambulance
Refraction
The change in direction of waves when they travel across a boundary
Occurs in all forms of waves (e.g. light, sound)
When a light ray travels from air into glass, the angle of refraction is smaller than the angle of incidence
Swimming pool appearing shallower than it is
water waves
White light
Diffraction
The spreading out of waves when they pass through a gap or round the edge of an obstacle
The narrower a gap is, the greater the diffraction
The wider a gap is, the greater the diffraction
Diffraction of light (e.g. telescope)
Diffraction of ultrasonic waves (ultrasound)
TV/radio reception