Two students perform an experiment to measure the frequency of vibration of a stretched wire. In the experiment a steel wire was stretched over two fixed wooden bridges. A small paper rider was placed on the wire. When student A placed a vibrating tuning fork, F1 on one of the bridges, no effect was noted. However, when student B placed another vibrating tuning fork, F2 on the bridge, the paper rider immediately jumped off. How do you explain what happend?
The Attempt at a Solution
After F1 was on the bridge, the wire should be oscillating at the frequency of F1. After F2 was installed, the wire is forced to oscillate a second time at a different frequency. Would it be correct to say the wire is oscillating at a frequency equal to the difference between F1 and F2? Given that the paper rider fell off, it was the case that the beat frequency equals the resonance frequency of the steel wire.
The other choice is to say that the wire is oscillating at a frequency equal to the combined frequency of F1+F2. But that wouldn’t work because imagine you had two vibrators both oscillating at the same frequency f. The wire would still be oscillating at f no matter how many vibrators there are although the intensity is proportional to the number of vibrators.