Saved Bookmarks
| 1. |
Using Huygen's construction, draw a figure showing the propagation of a plane wave reflecting at the interface of the two media. Show that the angle of incidence is equal to the angle of reflection. |
|
Answer» Solution :Laws of reflection by Huygen's PRINCIPLE : LET PQ be reflecting surface. Let a plane wavefront AB moving through the medium (air) towards the surface PQ meet at the point B. Let C be the velocity of ligh and t be the time of A to reach A' then A A =ct. By the Hugygen's principle, secondary wavelets starts from B and cover a distance ct in time t and reaches at B'. To obtain new wavefront, draw circles with point B as centre and ct (A A '=BB') as radius. Draw a tangent A 'D from the point A'. Then A ' D represents the reflected wavelets which travel at right angle. Therefore, incident wavefront AB and reflected wavefront A'D and normal lies in the same plane. In `Delta ABAand Delta DBA`'. ` A A '=BD =ct` `BA '=BA'["Common"]` ` angle BAA '=angle BDA' ["each" 90^@]` ` therefore Delta ABA 'approx Delta DBA ["by "R.H.S]` ` angle ABA =angle DA B [C.P.C.T]` ` therefore` incident angle `i -` reflected angle r ` angle i=angle r` Hence, the laws of reflection is proved. 
|
|