Summary Sinusoidal wave on a string

Wavefunction

Superposition of Waves For more than one wave on a string, add the wavefunctions together. This is called the superposition, which means to add.

Reflection at a boundary When a wave reflects from a fixed boundary, the reflected wave is inverted (i.e. upside down or the negative of the wavefunction).

Standing Wave A node is a point on the string that oscillates with zero amplitude. An antinode is a point on the string that oscillates with maximum amplitude. A standing wave is produced by two waves of the same amplitude, frequency, and phase traveling in opposite directions.

Standing waves with nodes at both ends

Harmonics

Speed of a wave on a string For a standing wave on a string, the speed has to be just right. The speed of any wave is The speed of a wave on a string depends on the tension and the linear density of the string

Guitar String A guitar string mostly vibrates with the fundamental standing wave (and a few harmonics added in with it; this is called superposition). The frequency of the fundamental depends on L, T, and the linear density of the string.

Poll How many nodes and antinodes does this standing wave have? 5 nodes, 4 antinodes 4 nodes, 4 antinodes 5 nodes, 5 antinodes 3 nodes, 2 antinodes 6 nodes, 5 antinodes

Poll If the length of the string is 2 m, what is the wavelength of the wave? 0.5 m 1.0 m 1.5 m 2.0 m 4.0 m

Poll What harmonic (N) is a standing wave with this shape? 2 3 4 5 6

Poll If you decrease the length of a guitar string by pressing on one of the frets with your finger, the frequency will Increase Decrease Remain constant

Poll If you decrease the tension in the string by turning the key on the neck of the guitar, then the frequency will Increase Decrease Remain constant

Poll The B string has a lower linear density than the A string on a six-string guitar. For which string, does the fundamental standing wave have the lowest frequency? B string A string Neither, they vibrate with the same frequency.

Longitudinal Standing Wave

Displacement node is a pressure antinode

Boundary conditions: closed pipe

Boundary conditions: open pipe

Pipe closed at one end and open at the other end

Pipe open at both ends

Poll At the open end of a pipe, the is a node and the is an antinode. pressure, displacement displacement, pressure None of the above; both displacement and pressure are nodes None of the above; both displacement and pressure are antinodes.

Poll At the closed end of a pipe, the is a node and the is an antinode. pressure, displacement displacement, pressure None of the above; both displacement and pressure are nodes None of the above; both displacement and pressure are antinodes.

Poll What is the harmonic (N) for the standing wave shown below. 3 4 5 6 7

Poll What is the harmonic (N) for the standing wave shown below. 1 3 5 7 9