Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.

[PHYSICS] Stroboscope

When viewing a transverse wave through a stroboscope with a frequency 10 Hz, the waves seem to be frozen, but the wavelength does change. If given that the frequency of the waves is within 39 Hz, state two possible frequency of this wave.

我寫5 Hz 同2.5 Hz, 但係佢話係10 同20. 唔明....

請高人指點

Update:

But the wavelength does change...

Why the wavelength changes??? I don't understand why the wavelength changes and the wave is frozen.

1 Answer

Rating
  • 天同
    Lv 7
    1 decade ago
    Favorite Answer

    The travelling wave wil be viewed as frozen (i.e. stationary) when a crest has just travelled a distance of one wavelength, such that it is now at the position of the crest ahead of it.

    But the time taken for the crest to travel one wavelength forward is one period. Therefore, if the wave period is 1/10 s, equal to that of the stroboscope, the wave will appear as frozen. Thus, 10 Hz is the first wave frequency.

    Suppose the crest travels exactly two wavelengths, it will be at the position of the crest two wavelengths ahead of it. The time required is two periods, thus 2T = 1/10 s or T = 1/20 s , which corresponds to a wave of frequency 20 Hz

    5 Hz is definitely not the answer, as a crest takes 1/5 s = 0.2 s to travel one wavelngth forward. But the stroboscope flashes at intervals of 0.1 s, thus when the stroboscope flashes, the crest only travels half a wavelength, at the position of the trough ahead of it. The wave doesn't appear frozen.

Still have questions? Get your answers by asking now.