1. Waves B2.01

2. Measuring waves Displacement Amplitude Wavelength Period Frequency
Phase difference

3. A Wave is…
…the transfer of energy through a medium without the net transfer of the medium

4. Aims
Describe the oscillation of the particles of the medium for a progressive wave
Be able to label amplitude, wavelength, period.
Be able to use c = f λ
Know the definitions and examples of longitudinal and transverse waves.
Describe polarisation, using a diagram

5. Label an arrow to show how point A oscillates
Wave Direction 
Amplitude 
Label an arrow to show how point A oscillates
Label amplitude of point B
Label wavelength from point B, label it 
Label one wavelength from point C, also label it 
Describe how the oscillation of particle A compares with the direction of motion of the wave
State whether particle B is about to move down or up as the wave passes through it
Describe the motion of particle C over the next full cycle of movement
Perpendicular
Down
Up, then down, before returning to original position

6. Examples of transverse waves
Electromagnetic waves
Ripples on water
Waves on ropes
Secondary earthquake waves (S-waves)

7. ag Label an arrow to show how point A oscillates
Wave Direction ag  
Label an arrow to show how point A oscillates
Label one wavelength from point B, label it 
Label one wavelength from point C, also label it 
Now write these in the box below the diagram you have just labelled
Describe how the oscillation of particle A compares with the direction of motion of the wave
What is the Displacement of particle B has travelled after one complete wave has passed through it
State how far the energy carried by the wave has travelled after one complete wave has passed through point B.
Parallel 0m
One Wavelength

8. Examples of longitudinal waves
Sound
Primary earthquake waves (P-waves)

9. Using the two wave equations
Fill in the table:
Now complete these in the box below the table
If a wave travels along a string with a wavelength of 0.75m and a frequency of 20Hz, calculate its speed.
If an object oscillates once every 0.02 seconds calculate its frequency and the wavelength of sound leaving this object at a speed of 330 ms-1
Calculate wavelength of wave with speed 3.0x108 ms-1 and frequency 88.3MHz
Try to explain in words why frequency x wavelength = speed
symbol
Stands for….
Measured in.. c f λ T
Wave speed
m s-1
Frequency
Hz ( = s-1)
Wavelength m
Time Period s
20 x 0.75 = 15 ms-1
f= 1/T = 50Hz ;  = 330 / 50 = 6.6 m
 = 3.0x108 / 88.3x106 = 3.4 m
f = 1/T; because Speed = Distance / Time, Speed = Distance x Frequency

10. Now write these in the box below the diagram you have just labelled C
Wave Direction D
In-phase
with B
In-antiphase
with B
Ideas of PHASE
Label next point along the wave that is in phase with B. (We say that this has a phase difference of 0° or say that they are in phase)
Label next point along the wave that is ½ cycle out of phase (this is called antiphase) with B
Now write these in the box below the diagram you have just labelled
Write the phase difference between points A and B as an angle, (remember 1 full cycle = 360° )
State whether this phase difference will stay the same or change over the next cycle of motion
What is the simplest way of expressing the phase difference between points B and D?
90
Same
180

11. Point to another region of rarefaction
Wave Direction A B C E D
The regions where particles are close together in a longitudinal wave are called regions of compression.
The regions where particles are spread out in a longitudinal wave are called regions of rarefaction.
What is the phase difference (in degrees) between points B (rarefaction) and C (compression)?
Point to another region of rarefaction
What is the simplest way of expressing the phase difference between points B and D?
180
180

12. Extended response time: a chance to practise your written skills… Answer the following taking care to use correct English
Using a long spring (stretched horizontally)it is possible to send longitudinal or transverse waves by oscillating one end. Describe:
How to move the end to create transverse waves
How to move the end to create longitudinal waves
The difference this will make to how each particle of spring moves
What is happening in terms of energy
What values could be measured about the movement of one end
How these values could be measured from the wave motion
Extra if finished:
- If you timed how long it took a wave to travel 10metres along the spring, explain how you could work out two extra values for this wave

13. Read each others… how well have they included these ideas
Read each others… how well have they included these ideas? (add ticks or comments in a different colour)
Using a long spring (stretched horizontally)it is possible to send longitudinal or transverse waves by oscillating one end. Describe:
How to move the end to create transverse waves… oscillate up and down, vertically
How to move the end to create longitudinal waves …oscillate forwards and back, horizontally
The difference this will make to how each particle of spring moves…
in transverse wave each particle oscillates perpendicular to direction of wave (or just up and down)
in longitudinal wave each particle oscillates parallel to direction of wave (or just forwards and back)
Overall, the particles do not change their mean positions
What is happening in terms of energy…..the energy of oscillating the end is transferred along the wave (you may notice some of it reflects back from the far end)
What values could be measured about the movement of one end
amplitude (how far up/down/forwards/back) from starting position it is moved
frequency (how many complete oscillations in each second)
How these values could be measured from the wave motion
amplitude (how far up/down/forwards/back from rest position any part of the spring moves)
frequency (how many complete oscillations any part of the spring makes each second)
Extra if finished:
- If you timed how long it took a wave to travel 10metres along the spring, explain how you could work out two extra values for this wave

14. Extra if finished: - If you timed how long it took a wave to travel 10metres along the spring, explain how you could work out two extra values for this wave Calculate wave speed using distance divided by time Calculate wavelength using wave speed divided by frequency (showing this in symbols is OK)

15. Polarisation

16. Polarisation

17. Polarisation can only happen for transverse waves
Now check pages in new CGP textbooks…then answer questions on p75 and 76

18. Most light you see is unpolarised
Reflected light is partially polarised (horizontally)
LCDs on calculators use polarised light.
Bolt systems 4
By horizontally, I mean that the plane of polarisation is horizontal, like this.
Imagine a bright sunny day. You’re on the beach and the sun is reflecting off the water. Aagh bright! I reach for my...polarising filters. What direction do I want the filter/slits?
Liquid crystal display

19. Aims
Describe the oscillation of the particles of the medium for a progressive wave
Be able to label amplitude and wavelength.
Be able to use c = f λ
Know the definitions and examples of longitudinal and transverse waves.
Describe polarisation, using a diagram

20. Homework You will be given a sheet to complete
Note that this is part of your numbered homework tasks on this week’s .
Please have it ready for collection in next week’s practical session (Monday or Tuesday lesson)
Any questions? Well done for today… more on waves this time next week