1. Progressive waves and wave properties
Longitudinal
Wave equation
Transverse
Progressive
Displacement
Compressions
Amplitude
Rarefactions
Wavelength
Frequency
Time period
Speed
Progressive Waves: longitudinal and transverse
Displacement, amplitude, wavelength, period, phase difference, frequency and speed of a wave.
Equation for frequency and period
Wave equation
Define and calculate intensity of a wave

2. CHALLENGE: What labels would the axes have?
Draw the axes shown and then starting from 0,0 draw a transverse wave. Then label each part of the wave that you can remember with the correct physics terminology
CHALLENGE: What labels would the axes have?

3. CHALLENGE: What labels would the axes have?
Draw the axes shown and then starting from 0,0 draw a transverse wave. Then label each part of the wave that you can remember with the correct physics terminology
CHALLENGE: What labels would the axes have?

4. Examples of waves p194-196 Transverse: Longitudinal: Sound waves
Water waves on surface
EM waved
Waves on a string
S- waves
Longitudinal:
Sound waves
P-waves

5. Questions
Define the following terms: Progressive wave Transverse Longitudinal
A wave in which the oscillations travel through a medium, transferring energy but not matter
A wave in which the oscillations move perpendicular to the direction of energy transfer
A wave in which the oscillations move parallel to the direction of energy transfer

6. Wave properties Term Symbol Unit Definition Displacement Amplitude
Wavelength
Period of oscillation
Frequency
Wave speed

7. Frequency and time period
𝒇=𝟏/𝑻
There is a simple relationship between frequency and time period (time for one complete oscillation):
Time period (s)
Frequency (Hz)
Draw two graphs showing waves of equal amplitude of 1.5m but with wave A having a frequency of 2Hz and wave B having a frequency of 6Hz

8. What is the unit for frequency in base units?
The wave equation
There is a very simple equation that shows the relationship between the speed of a wave and its frequency. To calculate the wave speed, you find the product of the wave’s frequency and wavelength.
Wave speed (ms-1)
𝒗=𝒇𝝀
Frequency (Hz)
Wavelength (m)
A surfer watches a set of waves pass by him. The waves have a frequency of 5 Hz and a wavelength of 2 m.
How many waves will he see in one second?
In one second how far will the front of this set of waves have travelled?
What is the unit for frequency in base units?

9. Reading Oscilloscopes
11.2 Wave Properties Calculation Sheet
PAG 5.3 Determining frequency and amplitude of a wave using an oscilloscope

10. Radians
A radian is an alternative way of describing a very particular angle that a point has passed through as you navigate around a circle.
It is equivalent to about 57.3◦ and is the angle subtended once you have travelled an arc length equal to the radius of the circle.
Degrees
Radians
360° 2π
180°
90°
60°
A whole circle (aka. A whole cycle of a wave) is equal to 2π radians
Careful! When using radian mode on calculator, make sure to put back in degree mode for future use!

11. Phase
All points in a wave will be at some point through their cycle.
This particular point is known as its phase.
One full phase cycle of a wave (360°) is one full wavelength (λ) which is 2π rads
What would each peak therefore represent in
Radians
Wavelengths
degrees
Delta

12. So in this example, the top wave is π/2 ahead of the bottom one!
Phase Difference
Phase Difference is the difference in phase(measured in radians) between one point of a wave and the same point on another wave of identical frequency (coherent) that started at the same time
So in this example, the top wave is π/2 ahead of the bottom one!

13. Examples
What is the phase difference between waves A and B in each of these examples?

14. Intensity= Power Area Intensity
Intensity is defined as the power per unit area:
Intensity= Power Area
Units:
Calculate the intensity of a sound wave 5.0 m from a source of power W.

15. Inverse Square Law

16. Intensity and amplitude
As sound spreads out from a speaker the intensity decreases as the energy becomes more spread out. This would results in the amplitude of the sound decreasing which means it would be quieter.
Halving the amplitude means halving the velocity of the particles in the wave, thus reducing the kinetic energy to a quarter..
This leads to the relationship
Intensity ∝ (Amplitude) 2

17. Question 1
A car stereo has two front speaker, each rated at 60 W. Find the intensity of the sound waves produced by one 60 W speaker at a distance of 1.0 m from the speaker, at its maximum power. Find the intensity of the sound waves produced by this speaker at a distance of 1.5 m, at its maximum power.
4.8 Wm-1
2.1 Wm-1

18. Question 2
A wave of amplitude 2 cm has an intensity of 320 Wm-2 when received at a distance of 2.0 m from the source. At a distance of 8.0 m calculate the
Intensity
Amplitude
20 Wm-2
0.5 cm