Total Internal Reflection and Critical Angle
When light travels from a medium with a higher refractive index to one with a lower refractive index, Snell's law seems to require in some cases (whenever the angle of incidence is large enough) that the sine of the angle of refraction be greater than one. This of course is impossible, and the light in such cases is completely reflected by the boundary, a phenomenon known as total internal reflection. The largest possible angle of incidence which still results in a refracted ray is called the critical angle; in this case the refracted ray travels along the boundary between the two media.
For example, consider a ray of light moving from water to air with an angle of incidence of 50°. The refractive indices of water and air are approximately 1.333 and 1, respectively, so Snell's law gives us the relation
which is impossible to satisfy. The critical angle θcrit is the value of θ1 for which θ2 equals 90°:
Read more about this topic: Snell's Law
Famous quotes containing the words total, internal, reflection, critical and/or angle:
“The totality of our so-called knowledge or beliefs, from the most casual matters of geography and history to the profoundest laws of atomic physics or even of pure mathematics and logic, is a man-made fabric which impinges on experience only along the edges. Or, to change the figure, total science is like a field of force whose boundary conditions are experience.”
—Willard Van Orman Quine (b. 1908)
“The real essence, the internal qualities, and constitution of even the meanest object, is hid from our view; something there is in every drop of water, every grain of sand, which it is beyond the power of human understanding to fathom or comprehend. But it is evident ... that we are influenced by false principles to that degree as to mistrust our senses, and think we know nothing of those things which we perfectly comprehend.”
—George Berkeley (1685–1753)
“And since the average lifetime—the relative longevity—is far greater for memories of poetic sensations than for those of heartbreaks, since the very long time that the grief I felt then because of Gilbert, it has been outlived by the pleasure I feel, whenever I wish to read, as in a sort of sundial, the minutes between twelve fifteen and one o’clock, in the month of May, upon remembering myself chatting ... with Madame Swann under the reflection of a cradle of wisteria.”
—Marcel Proust (1871–1922)
“The critical spirit never knows when to stop meddling.”
—Mason Cooley (b. 1927)
“So much symmetry!
Like the pale angle of time
And eternity.
The great shape labored and fell.”
—N. Scott Momaday (b. 1934)