Because the standing wave is constrained by the boundary of the string (the boundary of the string is fixed, and the string can never move or vibrate on the boundary), the frequency and wavelength of the standing wave can only take a series of specific discrete values. (In simple harmonics, if there are no other constraints, the frequency and wavelength can be arbitrarily selected. )
In fact, in physics and mathematics and other related fields, wave is the result of repeated oscillation of field values near stable equilibrium values (static values) due to the interference of one or more fields. Waves can transmit energy or information from one place to another.
Common waves are mechanical waves, which can only propagate through media, such as waves propagating along a rope. The most common mechanical wave is sound wave.
Sound is produced by the vibration of sound source. In class, tuning forks are generally used to demonstrate the generation and propagation of sound waves. When the tuning fork is struck, its sharp teeth vibrate back and forth, disturbing the surrounding air molecules. These disturbances are transmitted to adjacent air molecules through particle interaction, so that the sound generated by the tuning fork can spread through the air (medium).
Not all waves need a medium to propagate, for example, electromagnetic waves can propagate in a vacuum. Electromagnetic wave is generally a changing electric field generated by the change of charge speed, which generates a magnetic field, and then changes the magnetic field to generate an electric field. This interaction between induced electric field and magnetic field will lead to the propagation of electromagnetic waves in space. Electromagnetic waves with different frequencies have different names, and the order of increasing frequency is: radio wave, microwave, infrared radiation, visible light, ultraviolet ray, X ray and γ ray.
Standing wave characteristics
(1) The voltage and current are not only 90 degrees different in time. The spatial difference is also 90;
(2) The average power is zero, so it cannot be used to transport electromagnetic energy;
③ It has an antinode and a node whose position does not change with time, and the distance between the node and the adjacent antinode is λ/2.
④ The input impedance is pure imaginary, and the resistance varies with the length of the transmission line.
take for example
The distance of 5 meters is half the wavelength of 34Hz (the sound speed is 340 meters per second divided by the frequency of 34Hz, which is the full wavelength of 10 meter), so the length will be 2, 3, 4, 5, 6, 6 of 34Hz. Standing waves sometimes occur. That is, at 34 Hz, 68 Hz, 102 Hz, 136 Hz? Standing waves are generated in the same place.