Mathematics · Advanced university
Angular frequency of a wave-equation mode
For a string with fixed endpoints, length L, wave speed c, and positive integer mode n.
Method and conditions
For a string with fixed endpoints, length L, wave speed c, and positive integer mode n.
ωₙ = cnπ/L
Worked examples
A fixed-end string of length 12 m has wave speed 2 m/s. Write the angular frequency of mode n=10 as aπ rad/s. Find a. Round the final result to 4 decimal places if needed.
The wavenumber is nπ/L. Multiply by c = 2, giving (20/12)π rad/s.
1.6667
A fixed-end string of length 2 m has wave speed 41 m/s. Write the angular frequency of mode n=10 as aπ rad/s. Find a. Round the final result to 4 decimal places if needed.
The wavenumber is nπ/L. Multiply by c = 41, giving (410/2)π rad/s.
205
Try it
A fixed-end string of length 6 m has wave speed 5 m/s. Write the angular frequency of mode n=9 as aπ rad/s. Find a. Round the final result to 4 decimal places if needed.
A fixed-end string of length 4 m has wave speed 7 m/s. Write the angular frequency of mode n=5 as aπ rad/s. Find a. Round the final result to 4 decimal places if needed.
Check your work
Answers and marking notes
- 7.5
The wavenumber is nπ/L. Multiply by c = 5, giving (45/6)π rad/s.
- 8.75
The wavenumber is nπ/L. Multiply by c = 7, giving (35/4)π rad/s.
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