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Wave Nature Of Light: Huygens Principle

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Question
ICSEENIPH12029756
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What is the shape of the wavefront diverging from a point source of light?

Solution

Spherical

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Question
ICSEENIPH12029797
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White light is passed through sodium vapours contained in a thin walled glass flask and the transmitted light is examined with the help of a spectrometer. The spectrum so obtained is:
  • Absorption spectrum 
  • Solar Spectrum
  • Band Spectrum 
  • Continuous Spectrum

Solution

A.

Absorption spectrum 

Question
ICSEENIPH12029823
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On the basis of Huygen’s wave theory, prove Snell’s law of refraction of light. Draw a neat and lebelled diagram. (Postulates of Huygen’s wave theory not required).

Solution

On the basis of Huygen's wave theory, the laws of refraction

Given : AEB is the incident wave front and DGC be the refracted wavefront.

BC = V1t  V1 = velocity of light in medium 1.

AD = V2t V2 = velocity of light in medium 2.
i) Existence of the refracted wave front DGC
BC over straight V subscript 1 equals fraction numerator E F over denominator V subscript 1 end fraction plus fraction numerator F G over denominator V subscript 2 end fraction 
ii) fraction numerator sin space straight i over denominator sin space straight r end fraction space equals space V subscript 1 over V subscript 2 

Construction : From the point F a perpendicular FH is dropped.

Proof: ΔABC + ΔFHC [By simple geometry these triangles are similar (A.A.A.)]
BC over HC space equals space fraction numerator A C over denominator F C end fraction space space space space space space space space... space left parenthesis i right parenthesis I n space increment A D C space plus space increment F G C comma space space space space fraction numerator A C over denominator F C end fraction space equals space fraction numerator A D over denominator F G end fraction space space space space space... space left parenthesis i i right parenthesis thin space space space space space space space space space space space space space space space space space space space space space space space space space space space space left square bracket Similar space by space AAA right square bracket From space eqns. space left parenthesis straight i right parenthesis space and space left parenthesis ii right parenthesis comma space BC over HC space equals space AD over FG space equals space fraction numerator straight V subscript 1 straight t over denominator HC end fraction space equals space fraction numerator straight V subscript 2 straight t over denominator FG end fraction space space FG over straight V subscript 2 space equals space fraction numerator BC space minus space BH over denominator straight V subscript 1 end fraction FG over straight V subscript 2 space equals space fraction numerator BC space minus space EF over denominator straight V subscript 1 end fraction space open square brackets BH space equals space EF close square brackets FG over straight V subscript 2 space space equals space BC over straight V subscript 1 space minus space EF over straight V subscript 1 FG over straight V subscript 2 space equals space EF over straight V subscript 1 space equals space BC over straight V subscript 1 space Existence space of space wavefront space is space confirmed. space In space increment space ABC comma space sin space straight i space equals space BC over AC space space space space space space... space left parenthesis iii right parenthesis In space increment space ADC comma sin space straight r space equals space AD over AC space space space space space... space left parenthesis iv right parenthesis Dividing space equation space left parenthesis iii right parenthesis space by space Eq. space left parenthesis iv right parenthesis fraction numerator sin space straight i over denominator sin space straight r end fraction space equals space BC over AD fraction numerator sin space straight i over denominator sin space straight r end fraction space equals space fraction numerator straight V subscript 1 straight t over denominator straight V subscript 2 straight t end fraction straight mu subscript 2 space equals space fraction numerator sin space straight i over denominator sin space straight r end fraction space equals straight V subscript 1 over straight V subscript 2 Thus space Snells apostrophe straight s space law space is space confirmed. space Hence space proved. space 

Question
ICSEENIPH12029855
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State any one postulate of Huygen’s wave theory.

Solution

Huygen's wave theory states that every particle of the medium situated on the wavefront acts as a new wave source from which the fresh wave originates. These waves are called secondary wavelets.

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