IIT JEE , AIEEE Forum - Physics , Optics

sneha

I have a problem in understanding huygen's construction.

i m unable 2 trace d events that happen during the formation of a wavefront from another...

My understanding of "wavefronts" is also blurr......can smeone plss help me....

i m unable 2 grasp d concept....it ll be nice if smeone can give me a good explanation...

001sri

wave fronts r the form or shape of light waves which is spherical.
hygens principle states light as a mechanical wave travelling in a medium thought of as ether(we dont have to do anything wid it).
now as this wave travell in this medium it is propagated as a disturbance and as we observe in the case of sound waves vibrating particles vibrate others to transfer energy(as usual)

so as wave passes through a point the point becomes the virtual source of light mechanical waves and this is considered as secondary source of light or new wave fronts r assumed to b originating from this point called secondary wavelets.

let me know if u r satisfied or want more explanation

001sri

one thing i left in my last post was the construction aspect.

now since these wavelets r spherical so they will superimpose n interfere constructively n destructively.these newly formed waves can b thought of as moving in such a way which give us a feeling that a large envelope is spreading in forward direction(directionof propagation) considering large no.of wave fronts included in the envelope.
u can imagine it just like ripples in water considering each "circle" as an envelope which is made up oftiny wavelets.

now come to the construction point of view.
when we draw a wave front we consider it so large that it becomes same(almost)the tangent at the surface of wave front
and this the straight line which u see in books for refraction or reflection.

hope nothing is left now.

everybody let me know their opinion as
it is quite conceptual part of JEE syllabus

magiclko

and what if a spherical wave-front is reflected back by a spherical or plane mirror???

krishna.gopal

Good work Sri. And mansi as far as reflection is concerned don't worry about reflection by construction (The basic concept remains same but construction will not be so straight forward) Remember the fact that light propogation is perpendicular to wavefront. You know direction of light propogation by ray optics and hence you can always tell the shape of wave front

001sri

if u take the radius of curvature as big as the radius of wave front it will converge back to the source(converging mirror)
we here r speaking of an extreme ideal case!
otherwise take the wavefront as planar(almost) waves and it willbecome curved after reflection(refer FIITJEE Q paper.)

001sri

sorry it will become curved in case of only curved mirrors but remains planar in case of plane mirrors.

another concept useful to understand this is look it veerry very closely and find out the position of different parts of the wave-front just before n just after reflection.
i mean the part of wave front close to optical centre will take most time to reflect than those at the peripheri in case of concave mirror.

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