experimental-physicsharmonic-oscillatorresonance
I carried out this experiment in class:
I struck a tuning fork with a hammer. The sound lasted for some time.
However, when I connected the tuning fork onto a wooden sounding box, the sound lasted for a few seconds (much shorter than the previous case)
But why is that? I know the reason is because of resonance but can someone please explain the reasoning behind these observations with detail.
Nope. The frequency of the tuning fork doesn't depend on the force with which it's struck. Every tuning fork has its own desired frequency. And hence, people usually say, "Hey - take that fork, the one with 432 Hz (an example) on it...".
The oscillations usually get damped out after some period. But, the frequency still remains the same... Usually, the frequency of a tuning fork depends only on the property of its material.
If you have a look at the Wikipedia article on frequency, the frequency turns out to be
$$F \propto \frac{1}{l^2}\sqrt{\frac{EI}{\rho A}},$$
where $F$ is the frequency, $l$ is the length of the tines, $E$ is the Young's modulus of the material (which is related to stiffness), $I$ is the second moment of area of the tines (which is related to inertia), $A$ is the cross-sectional area of the tines and $\rho$ is the density of the material.
This clearly shows that the parameters are all the properties of the material from which the fork is made, as well as its shape.
Why does maximum resonance occur at triple the length of air column for the previous maximum resonance?
Because resonance in a pipe that is closed at one end occurs when a standing wave of air is generated within the pipe, and this can only happen if the open end of the air column is a displacement antinode (where the wave is at its max amplitude), while the closed end of the air column is a displacement node (where the wave has zero amplitude). If you try to fit a sinusoid into a pipe of a certain length with these constraints, then you get a sequence of possible standing waves as shown in the following diagram:
As you can see, the first possibility is that one quarter of a wavelength $\lambda$ fits in the pipe, while the second possibility is that three quarters of the wavelength fits in the pipe. In other words, in the second case the pipe must be three times as long as in the first as you indicated.
Also, if the reflected wave is out of phase with the incident wave, will the sound waves really cancel each other out, producing no sound at all?
Yes. The amplitudes of the two waves add together. If the waves are completely out of phase, then at every point in space, the amplitudes of the waves will have opposite sign, so when you add the amplitudes, they cancel.
can I somehow match two light waves out of phase with each other to cancel each other out?
Yes. There is a very famous experiment, the double slit experiment, where this actually happens. In fact, it's not to hard to perform this experiment at home. See the following physics.SE question:
Is it possible to reproduce Double-slit experiment by myself at home?
Best Answer
A vibrating tuning fork contains a finite amount of vibrational energy. As it generates sound waves, this vibrational energy is transferred to the air as sound waves. As this energy is used up, the tuning fork grows quieter until it can no longer be heard.
A sounding board is designed to increase the amount of sound produced by a vibrating item (usually a string.) The increase in sound is offset by an increase in energy transference. Because more energy is leaving the tuning fork as sound, the tuning fork grows quieter, faster.