![]() As the waves interact at low angle with the surface of this tunnel they are reflected toward the focus point (or toward another interaction with the tunnel surface, eventually being directed to the detector at the focus). X-ray telescopes are constructed by creating a converging "tunnel" for the waves. Total internal reflection is used as a means of focusing waves that cannot effectively be reflected by common means. Total internal reflection of light from a denser medium occurs if the angle of incidence is greater than the critical angle. This is analogous to the way impedance mismatch in an electric circuit causes reflection of signals. Solving Maxwell's equations for a light ray striking a boundary allows the derivation of the Fresnel equations, which can be used to predict how much of the light is reflected, and how much is refracted in a given situation. In the most general case, a certain fraction of the light is reflected from the interface, and the remainder is refracted. In fact, reflection of light may occur whenever light travels from a medium of a given refractive index into a medium with a different refractive index. The law of reflection states that θ i = θ r, or in other words, the angle of incidence equals the angle of reflection. By projecting an imaginary line through point O perpendicular to the mirror, known as the normal, we can measure the angle of incidence, θ i and the angle of reflection, θ r. In the diagram, a light ray PO strikes a vertical mirror at point O, and the reflected ray is OQ. Reflection also occurs at the surface of transparent media, such as water or glass. Reflection is enhanced in metals by suppression of wave propagation beyond their skin depths. Ī mirror provides the most common model for specular light reflection, and typically consists of a glass sheet with a metallic coating where the significant reflection occurs. In specular reflection the phase of the reflected waves depends on the choice of the origin of coordinates, but the relative phase between s and p (TE and TM) polarizations is fixed by the properties of the media and of the interface between them. ![]() ![]() I am inclined to believe it's the second situation.Reflection of light is either specular (mirror-like) or diffuse (retaining the energy, but losing the image) depending on the nature of the interface. But it would be "more similar" in size to the first reflection (compared to situation 1 above). Depending on the curvature and distance of the panes, the size and position of the second reflection may vary. This would give you a second smaller reflection "almost exactly" superposed on the first. That would give you this second scenario: And in my experience on subways, these panes are often not very flat. In particular if the second pane was slightly curved, this would give you a "second, smaller" image. It is also possible (hard to tell from your description) that you were just seeing reflections from two panes on the same side. In reality it doesn't take much of an angle - and in fact if the first window is slightly curved it can help put R3 back "on top of" R1. I showed an exaggerated angle of the windows, so the reflection "can get past you". R2 is the "reflection of the reflection" (in the window behind you). When using windows as mirrors, we can draw virtual reflections (labeled R1, R2 and R3). This diagram may help understand the answer given by H better:
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