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If two electromagnetic waves have same wavelength, does that implies both of them have same frequency and intensity?

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closed as unclear what you're asking by ACuriousMind, Emilio Pisanty, user36790, CuriousOne, David Hammen Jul 14 '16 at 15:43

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  • $\begingroup$ Read your question - you state the answer... Whether they have the same frequency would require that they travel in the same medium. $\endgroup$ – Floris Jul 13 '16 at 15:41
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Yes, two EM waves with the same wavelength would have the same frequency. Frequency and wavelength are inversely related, by the formula $\nu = \frac{c}{\lambda}$, where $\nu$ is frequency, $\lambda$ is wavelength, and $c$ is the speed of light. Therefore, if two waves have the same wavelength, they will have the same frequency.

The intensity of the wave, however, is a function of the energy density of the wave, which in turn depends on the amplitude of the magnetic and electric fields. These amplitudes are independent of frequency/wavelength.

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    $\begingroup$ (Note, on the other hand, that if the two waves are compared in different media, and particularly over different refraction indices, then equal wavelengths will correspond to different frequencies.) $\endgroup$ – Emilio Pisanty Jul 13 '16 at 20:05
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The frequency can change ("still there is a frequency shift") while the wavelength remains unchanged ("the distances between subsequent pulses are not affected"):

http://www.einstein-online.info/spotlights/doppler Albert Einstein Institute: "Here is an animation of the receiver moving towards the source:

http://www.einstein-online.info/images/spotlights/doppler/doppler_detector_blue.gif

By observing the two indicator lights, you can see for yourself that, once more, there is a blue-shift - the pulse frequency measured at the receiver is somewhat higher than the frequency with which the pulses are sent out. This time, the distances between subsequent pulses are not affected, but still there is a frequency shift."

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    $\begingroup$ Nope, that's incorrect. In the frame of the detector, the wavelength also changes, so that $c=\lambda/\nu$ whenever both are measured on the same inertial frame. $\endgroup$ – Emilio Pisanty Jul 13 '16 at 20:07
  • $\begingroup$ "In the frame of the detector, the wavelength also changes" No it doesn't. The frequency and the speed of the light relative to the observer change, in violation of Einstein's relativity. See this: farside.ph.utexas.edu/teaching/315/Waveshtml/node41.html "Thus, the moving observer sees a wave possessing the same wavelength [...] but a different frequency [...] to that seen by the stationary observer." $\endgroup$ – Pentcho Valev Jul 14 '16 at 7:30
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    $\begingroup$ Given that the spectrometers used to measure Doppler shift of Astronomical objects are sensitive to wavelength, I can assure you that physicists know how this works. When the frequency changes so does the wavelength. $\endgroup$ – dmckee Jul 15 '16 at 0:22

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