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You need a reflector (at least roughly parabolic) to focus the heat. To be effective, the reflector must be substantially larger than your IR source. You cannot efficiently collimate radiation using o …

It's a semi-arbitrary choice. Not completely arbitrary since, in practice, we more commonly sense EM waves by their electric fields rather than their magnetic fields.

Sure, but the diffraction limited resolution of such a system is about half a wavelength. The wavelength at 100 MHz (not a terribly low radio frequency) is 3 meters.

When you're dealing with wave phenomena, forget photons and use wave models. Babinet's Principle is more illuminating than Huygens' here. Objects of size comparable to the wavelength are very effectiv …

You might look at Thomson scattering, the classical interaction of an electromagnetic wave with a single charged particle. Response to comment: Trying to understand the collective interaction of a bun …

This is an example of the math not fully capturing the physics. What we observe in reality is that every EM field in the universe has a source somewhere. The source may be a long way from where we det …

There are many processes involved in penetration of matter by electromagnetic radiation. At 2.4 GHz, the principal mechanism limiting the penetration depth is often ohmic dissipation of induced ionic …

It's a model. All models have limitations. Sometimes, a scalar wave model is adequately insightful for a vector wave problem, sometimes it isn't. A scalar model of light diffraction is fine for a came …

Even narrow slits are very leaky to radiation polarized perpendicular to them unless they are short compared to a wavelength. They function as slot antennas, coupling the inside of your enclosure to t …

A microwave oven isn't a Faraday cage: there's a gap all around the door, narrow but much longer than a wavelength. Microwaves can easily leak through such a gap. However, the edge of the microwave do …

Once you get away from bright, hot things like stars, the dominant radiation is the 2.7K cosmic background. That uniformly irradiates everything in a flux you may calculate using the Stefan-Boltzmann …

Long radio wavelengths >~1 km, can't penetrate the ionosphere. The situation at infrared wavelengths is complicated, where there are bands where the atmosphere is opaque, but "windows" where it isn't. …

Waves don't necessarily have a wavelength or frequency. But any wave may be decomposed through Fourier analysis into periodic components that do have a wavelength and frequency.

The router converts this WiFi signal into a long-range signal. This signal can traverse the length of the Earth. No, the route usually goes via more than one router, and the signal only has to reach …

Your wiggly red line represents the magnitude of the field, not a physical motion. Its amplitude declines with distance from the antenna.