# Can there be resonance in electromagnetic waves?

So, resonance is created in sound waves when a body is made to vibrate by an external force at its natural frequency, the result is a build-up amplitude and higher intensity of sound. Similarly can we create resonance in electromagnetic waves, to build up their intensity by applying external force.

• Like a laser cavity? – Jon Custer Aug 31 '17 at 16:48
• @JonCuster I am completely unaware of this term? – Ajinkya Naik Aug 31 '17 at 16:48
• You can also look up terms like "optical cavity", "optical resonator", "dielectric resonator", "Fabry-Perot", ... – Steve Byrnes Aug 31 '17 at 16:55
• – anna v Aug 31 '17 at 17:00
• Look up 'cavity magnetron'. – tfb Aug 31 '17 at 22:16

Electromagnetic waves can be brought to resonate in a cavity (in both optical and Microwave/RF regimes) much in the same way sound waves resonate in an acoustic cavity. Subject to boundary conditions the wave (electromagnetic) has to end at the cavity wall and hence the cavity can only support integer number wavelengths of the frequency at which the EM wave oscillates. For example, a 1 dimensional cavity supports a mode described by the following expression: $$E(x) = E_0 sin(\frac{n \pi x}{L})$$