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4.2 Travelling waves
4. Oscillations and waves
Investigating the relationship between the frequency and wavelength of a
travelling wave
Background
“A
wave is a propagating dynamic disturbance of one or more quantities, sometimes as described
by a wave equation. Waves can be periodic, in which case those quantities oscillate repeatedly
about an equilibrium (resting) value at some frequency. When the entire waveform moves in one
direction it is said to be a traveling wave; by contrast, a pair of superimposed periodic waves
traveling in opposite directions makes a standing wave.
”
Source:
https://en.wikipedia.org/wiki/Wave#Traveling_waves
Equipment: Waves on a string simulation phet simulation (
shorturl.at/qJUVW
)
Method
1.
Select ‘Oscillate’, ‘No End’, make ‘Damping’ none and select ‘Ruler’
2.
Line up the ruler with a green particle.
3.
Change the frequency to 1.00 Hz, the amplitude can remain at 0.75 cm.
4.
Measure the wavelength using the ruler and record your data.
5.
Change the frequency to 1.50 Hz. Make a qualitative observation. Repeat with increasing
values of f.
6.
Once you have collected all your data please play with the simulation to see the effect of
damping and tension on the oscillation.
7.
Convert the wavelengths from cm to m and plot the data.
Table of results
Analysis
Frequency / Hz
Wavelength / cm
Wavelength / m
1.50
1.75
2.00
2.25
2.50
2.75
3.00
4.2 Travelling waves
4. Oscillations and waves
We can linearise the date by plotting 1/f against λ. Add the column heading and compete the
calculations.
Analysis
Calculate the gradient by annotating the graph above and write it here. Include the units.
What does the gradient represent (look at the units!) and remember it is constant.
Derive an equation to show this relationship. Show your working.
Evaluation
Why did we start the frequency measurements at 1.50 Hz?
Why are error bars not included? Could we include them?
