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Essential idea: There are many forms of waves available to be studied. A common characteristic of all travelling waves is that they carry energy, but generally the medium through which they travel will not be permanently disturbed.
Nature of science: Patterns, trends and discrepancies: Scientists have discovered common features of wave motion through careful observations of the natural world, looking for patterns, trends and discrepancies and asking further questions based on these findings. (3.1)
General Resources:
General Resources:
Kognity Textbook Chap 4 - Use you ACS Login
IB Physics Site: Topic 4 - Comprehensive notes
IB Physics Site: Topic 4 - More notes
Topic 4 Flashcards - Vocab Devo.
Understandings:
Travelling waves
Wavelength, frequency, period and wave speed
Transverse and longitudinal waves
The nature of electromagnetic waves
The nature of sound waves
Applications and skills:
Explaining the motion of particles of a medium when a wave passes through it for both transverse and longitudinal cases
Sketching and interpreting displacement–distance graphs and displacement–time graphs for transverse and longitudinal waves
Solving problems involving wave speed, frequency and wavelength
Investigating the speed of sound experimentally
Guidance:
Students will be expected to derive c=fλ
Students should be aware of the order of magnitude of the wavelengths of radio, microwave, infra-red, visible, ultraviolet, X-ray and gamma rays
Data booklet reference:
c=fλ
International-mindedness:
Electromagnetic waves are used extensively for national and international communication
Theory of knowledge:
Scientists often transfer their perception of tangible and visible concepts to explain similar non-visible concepts, such as in wave theory. How do scientists explain concepts that have no tangible or visible quality?
Utilization:
Communication using both sound (locally) and electromagnetic waves (near and far) involve wave theory
Emission spectra are analysed by comparison to the electromagnetic wave spectrum (see Chemistry topic 2 and Physics sub-topic 12.1)
Sight (see Biology sub-topic A.2)
Aims:
Aim 2: there is a common body of knowledge and techniques involved in wave theory that is applicable across many areas of physics
Aim 4: there are opportunities for the analysis of data to arrive at some of the models in this section from first principles
Aim 6: experiments could include (but are not limited to): speed of waves in different media; detection of electromagnetic waves from various sources; use of echo methods (or similar) for determining wave speed, wavelength, distance, or medium elasticity and/or density
Intro Question:
Two children are standing at one end of a hall fighting over a toy. They both scream at the same time. Their mother, Amy, is at the other end of the hall. Del's scream has a frequency of 960 Hz. Cohen's scream has a frequency of 640 Hz. Determine whose scream reaches the mother first?
Del's scream
Cohen' scream
Both are heard at the same time
Neither is heard due to interference.
Wave Speed
Wave Speed
PIVOT Data
PIVOT Data
Data collected from the PIVOTinteractives Site:
Which type of mathematical relationship does the curve of the data points indicate?
What do the areas of the five different boxes tell us about the data collected?
What were some of the factors (variables) that impacted the wave speed in the PIVOT spring experiment?
What are factors (variables) that would impact the speed of sound in air?
Using the Speed of Sound to Measure Air Temperature
Using the Speed of Sound to Measure Air Temperature
The Speed of Sound in Air can be approximated by the equation to the right:
2. Repeat your data collection a minimum of 5x.
3. Using the measurements and proper calculations, determine the speed of sound in the cardboard tube.
4. Based on the temperature of the air in the cardboard tube and equation above, determine your relative error.
In Rm 260, determine the speed of sound in the cardboard tube using the LabQuest, microphone and an echo of your finger snap.
Enable Triggering and Set trigger level.
A second cardboard tube has been wrapped in black paper and set in the direct sun.
5. Using a similar procedure, determine the speed of sound in the cardboard tube.
6. Using the equation above, determine the temperature of the air in the paper covered cardboard tube.
7. Based on the thermometer in the tube, determine your relative error.
8. Suggest some ways of improving your results.
Speed of light
Speed of light
When applied to electromagnetic waves, like visible light, the symbol c is often used to represent the speed of light. In the IB data booklet the equation is stated as,
c=f𝜆
The speed of all electromagnetic waves in a vacuum is the same for as the speed of light in a vacuum. To three significant figures the speed of light in a vacuum is 3.00 x 108 m s-1.
The speed of light in air is assumed to be the same as the speed of light in a vacuum to three significant figures.
Measuring the speed of microwaves
Measuring the speed of microwaves
Microwaves are one type of electromagnetic radiation. Microwaves also travel at the speed of light. In this activity you will use the melting positions on a bar of chocolate in a microwave oven to determine the speed of the microwaves.
As the microwaves move back and forwards inside the oven they superpose causing spots of stringer heating that will melt the chocolate first. As shown in the diagram below, the distance between two melt spots on the chocolate represents half of the wavelength of the microwaves.
Take the turntable out of the microwave. Place the bar of chocolate on a plate and place it in the middle of the microwave oven.
Switch on the microwave oven at full power for about 15 - 20 seconds until you see the chocolate start to melt in two or three places.
Take out the chocolate and measure the distance between two adjacent melted spots. It may look like the photograph to the left.
Use this measurement to determine the wavelength of the microwaves in metres.
The microwaves in a microwave oven usually have a frequency of 2450 MHz (you may want to check the model you are using). If possible check this on the microwave oven itself. Use the wave speed equation
c=f𝜆
to calculate the speed of the microwaves in m s-1 and compare this with the accepted value of the speed of light.
Creating your own Waves on DESMOS
Creating your own Waves on DESMOS
Wave on a String - PhET Simulation
Wave on a String - PhET Simulation
Explore the following:
Switch to OSCILLATE
How do each of the following individually affect the motion of the wave?
Amplitude
Frequency
Damping
Tension
Fixed - Loose End
Everything below this is a work in progress, you are not responsible for any of the information below:
Everything below this is a work in progress, you are not responsible for any of the information below:
Audacity Speed of Wave:
Measuring the speed of sound
In this activity you will measure the speed of sound in air using microphones and the recording software Audacity. Audacity can be downloaded here.
Apparatus
Audacity (free open source recording software), sound source locators, USB microphone adaptor (if using macbook air), laptop.
Instructions
Plug the two microphones into the USB microphone adaptor and plug the adapter into a USB port on your laptop. Open Audacity only after you have plugged in the adapter to the USB port.
Set the microphone input to USB Audio Device and 2(Stereo) Input Channels, as shown below, so that it allows simultaneous display of both microphone inputs.
Click on the the Length check box to show the number of samples between the two graphs.
In order to notice the time delay you should click on the graph where the time delay occurs and then click on the Zoom In button until you can see a very obvious time difference as shown below.
Then click and drag on the recording from a point on the leading graph to a similar point on the second graph as shown below.
If the sampling rate is set at 176400 Hz this means that there are 176400 samples measured per second and the time between samples is 1/176400 seconds.
Click the red circle Record Button and make a sharp sound beyond one of the microphones so that the sound will travel into the microphones one at a time. You should notice that the nearer microphone gives a bigger signal than the further away microphone.
When you are happy with the recording click on the Stop Button .
The recording should look similar to the one shown below. On this time scale it looks as if there is no time interval between the sound received by each microphone.
Position the microphones a certain distance apart e.g. 1 metre and make sure that they are pointing in the same direction. Measure the distance as accurately as possible.
As the time for the sound to travel between the microphones is very short set the Sampling Rate (project rate) to a high value, for example 176400 Hz.
In the example above the length of the chosen section is 814 samples. The length of time for the sound to travel between the two microphones can now be determined from the product of the number of samples and the time between samples. e.g.
So the time for the sound to travel between the two microphones =0.00461 seconds
Now move the microphones a different distance apart and measure the time again in a similar way to before. Repeat this for 3 or 4 more distances.
Data Analysis
Plot a graph of distance (y-axis) against time (x-axis). The speed of sound can be found from the gradient of the line of best fit.
The speed of sound depends on room temperature. If you know the room temperature (i.e. measure it with a thermometer!) you can find out the theoretical value of the speed of sound in air use the following calculator from Hyperphysics website. Then compare this value with your gradient.
Wave propagation requirements
Wave propagation requirements
Sound v. Electromagnetic
Wave - Particle Duality intro
Possible Lab (dependent upon materials available)
Possible Lab (dependent upon materials available)
Wave speed - Choose 4 substances.
Properties of a medium that affect wave speed.
Measuring wave speeds
Sound (∆Temp, ∆Gas)
Solids (∆material, when does a material change?)
Choose 4 media: determine by method described in class the velocity of a wave with in the media.
Propose explanations for
the differences of speed within the media.
how could this concept be used in industry, medicine, or science
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