Physics Help Forum Question about refraction

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 Feb 4th 2009, 03:58 PM #1 Junior Member   Join Date: Feb 2009 Posts: 5 Question about refraction Hello, I've been searching for an answer to this question for hours, and no-one else seems ever to have asked it. So, if anyone could help that would be great... I understand the analogy of refraction involving a car driving, obliquely, across the boundary between two terrains - and that the difference in 'propagation' speeds affects the direction of the car - but i don't see how the car is a valid representation for a beam of light. The car 'bends' across the boundary because its particles are bonded together. If one of its sides slows down, the other side is inclined to remain attached - but what keeps the components of a light beam connected? What makes the wave front 'want' to remain a line? What stops one division of the front (possibly photons?) from speeding ahead (or falling behind) the divisions which have not yet reached the boundary? Thanks in advance...
 Feb 5th 2009, 07:38 AM #2 Junior Member   Join Date: Feb 2009 Location: india Posts: 14 waves which are in same phase ,in same direction form a wavefront. if you draw a plane perpendicular to direction of waves travelling it forms a wavefront.
 Feb 5th 2009, 07:58 AM #3 Junior Member   Join Date: Feb 2009 Posts: 5 Thanks Thankyou for the reply, but the question is still: why do these individual waves (forming these immaginary wavefronts) tend to stay in step (breaking the immaginary wavefronts)?
 Feb 5th 2009, 08:13 AM #4 Junior Member   Join Date: Feb 2009 Location: india Posts: 14 they do not remain in step we make them to make our calculations easy
 Feb 5th 2009, 08:30 AM #5 Junior Member   Join Date: Feb 2009 Posts: 5 My understanding was that the bending of a ray of light was due to the differece in speeds amoungst its component waves, if this is not true then why do individual waves bend at an interface?
 Feb 5th 2009, 09:06 AM #6 Junior Member   Join Date: Feb 2009 Posts: 5 Hope this is clear: Why does the first sittuation occur, and not the second?
 Feb 6th 2009, 07:57 AM #7 Junior Member   Join Date: Feb 2009 Location: india Posts: 14 [quote=ryansuchocki;3379] Why does the first sittuation occur, and not the second?[due to change in speed.(due to refractive index) so the waves bend towards normal and since wavefront has to be perpendicular so situation 2 occurs. i hope this answers the querry ]
 Feb 6th 2009, 10:36 AM #8 Junior Member   Join Date: Feb 2009 Posts: 5 Again, thanks for the reply: but you've just repeated what i've been asking about from the start. You said the change in direction happens 'due to change in speed' - but not WHY this happens. What scientific formula states 'speed = direction', and more to the point: says why! If you're tired of replying to this thread then just ignore me... I'm sure there's someone out there who's thought what i'm thinking before...
 Feb 6th 2009, 09:06 PM #9 Senior Member   Join Date: Apr 2008 Location: HK Posts: 886 Maybe you can watch the video below to know more about why there is change in speed YouTube - Lec 18 | MIT 8.03 Vibrations and Waves, Fall 2004
 Feb 7th 2009, 03:32 AM #10 Junior Member   Join Date: Feb 2009 Location: india Posts: 14 no i am not tired. well change in speed takes place due to refractive index n=c/v where n is refractive index of medium

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