4

Yes, silver reflects because of the difference of its refractive index from that of air. However, silver is different from air or vacuum in that it is a lossy medium: it is conductive, so electromagnetic waves propagating in it induce currents, thereby losing energy and decaying in amplitude. This is conveniently modeled by a complex refractive index: $$\...


2

Yes, there is. You can buy a sponge-like substance called open cell foam or fully reticulated foam which looks like a block of sponge but has a very large cellular structure in which all the cells are interconnected ("reticulated") with open passages. This stuff is used to fill the fuel tanks of race cars to prevent the fuel from flowing freely out ...


2

This is the same as asking what would happen if the sun couldn't get rid of the heat it generates. In that case, the heat builds up, the sun's temperature goes up, and in response the sun expands a bit. This expansion causes the fusion reactions in the sun's core to slow down, which slows down the rate of heat generation. But if none of that heat can escape, ...


1

The basic idea is, you can think of the mirror as a window, when you look through it, you see the symmetric version of your own dimension. If the mirror is on the x-axis, the objects distance to the mirror will be the same on both sides; if the object is at (4,9), its distance to the mirror is 9 units, meaning it will be 9 units away from the 'window' when ...


1

Simply putting the photons in a smaller box does not change the gravitational mass of the box + photons, because the box will contain the same amount of energy. This is not quite true, because when the photons are closer together they have lower gravitational potential energy, so the overall energy is very slightly reduced. On the other hand, putting the ...


1

What you have discovered is comatic aberration. It is similar to spherical aberration but occurs in both spherical and parabolic mirrors. If the incident rays are not parallel to the principal axis they are not focused to a point but rather to a comet shape which is the origin of the word coma, or comatic.


1

When the light rays reach our eyes (as you've depicted in your diagram) our brain doesn't know whether those light rays are being reflected off from a mirror, or is there a real object present behind that mirror. This is because the light rays from any real object and the reflected light rays cannot be distinguished because both of them are identical. Thus ...


1

The reflection efficiency is given by $$1 - |\Gamma|^2 = 1 - \left|\frac{Z_L - Z_0}{Z_L + Z_0}\right|^2$$ where $\Gamma$ is the reflection coefficient, $Z_L$ is the load (antenna) impedance and $Z_0$ is the characteristic impedance of the transmission line. Your third expression gives the correct efficiency.


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