# Tag Info

## Hot answers tagged optics

5

Yes, light can be brought to a complete halt under the right conditions. To understand how this happens you need to understand what is going on when light slows down in a medium. Light is an oscillating electromagnetic field, and when it passes though anything that contains charged particles (i.e. any matter made from electrons and protons) the electric ...

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Imagine the speed of light to be $1$ meter per second and the speed of light in the medium with a high refractive index to be $\frac{1}{2}$ meters per second. If you have a single peak of a wave in the slower medium, that peak must move forwards at speed $\frac{1}{2}$, no matter what angle it's facing. In the faster medium, that peak must move forwards at ...

2

The ideal perfectly smooth flat surface has translational invariance symmetry. That means that there is no mechanism for the scattering of a wave in the horizontal direction, and no mechanism for the change in the component of wave vector parallel to the boundary. That is, the horizontal component of wave vector is conserved. For light incident at angles ...

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I agree that's confusing, and that $\theta_2$ is just plain wrong. I've always seen it explained with the normal perpendicular to the surface, just like you say, and exactly as drawn in https://en.wikipedia.org/wiki/Snell%27s_law But note that this gives the same $\theta_1$ as in your drawing. But the way you've drawn your drawing, $\theta_2=\theta_1$, ...

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The green lines are wave fronts, not normal lines. You can think of the green lines as crests of the wave. That's why they're always perpendicular to the ray. Contrast this with normal lines, which are perpendicular to the surface. You're right, incident and refracted angles are always measured between the ray and the normal to the surface. This turns out ...

1

Answer Ray in red is the shortest path if and only if $\theta_I=\theta_R$ and light only travels in such path to reach point B via mirror. It is not a local minimum, because the shortest way, of course is a straight line connecting $A$ and $B$. Red line with $\theta_I = \theta_R$ is a stationary curve of the group of curves that go through A, B and a ...

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