Saved Bookmarks
| 1. |
Define a wavefront. Use huygen's principle to verify the laws of defraction. |
|
Answer» Solution :A wavefront is defined as a surface of constant phase. Consider a PLANE surface XY separating a rarer medium of refractive index `n_(1)` from a denser medium of refractive index `n_(2)` Let `c_(1)` and `c_(2)` be the values of speed of light in the two media. AB is a plane wavefront incident on XY at an angle `i`. Let at a given instant the end A of wavefront just strikes the surface XY but the other end B has still to COVER a path BC. if it takes time t, then `BC=c_(1)t`. According to Huygen.s principle point A meanwhile BEGINS to emit secondary wavelets which will cover a distance `c_(2)t` in second medium in time t. draw a circular arc with A as centre and `c_(2)t` as radius and draw a tangent CD from point C on this arc. then CD is the refracted wavefront, which advances in the direction of rays 1.2.. the refracted wavefront subtends an angle r from surface XY.  Now in `DeltaABC" "sini=(BC)/(AC)=(c_(1)t)/(AC)` and in `DELTAADC" "sinr=(AD)/(AC)=(c_(2)t)/(AC)`. `therefore (sini)/(sinr)=` `(c_(1)t//AC)/(c_(2)t//AC)=(c_(1))/(c_(2))=`a constant`=(n_(2))/(n_(1))=n_(21)`. which is snell.s law of refraction. |
|