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| Verification of Laws of Reflection on the basis of Huygen's Wave Theory |
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| Consider AB a plane incident wavefront on a mirror
M1M2. Let ÐBAA' =
Ði = be the angle of incidence. Every point on the wavefront AB is a source of secondary disturbance. Let the disturbance at B strike the mirror at A|. In a time t second when B reaches A|, the point A would have been reflected and will have traveled a distance of AB| such that AB|= BA| i.e., |
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| BA| = ct and AB| = ct. With A as centre, draw an arc of radius ct. Repeat for points D and others on AB. From A| draw a tangent to these arcs (dotted) as shown. A|B| therefore represents the reflected wavefront. To make sure A|B| is the reflected wavefront one should prove that |
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| DP + PD| = BA| |
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| Draw PN to BA| |
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| DP = BN |
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| In Ds ABA| and AA|B| |
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| AA| is common |
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| Also BA| = AB| = ct and so the triangles are congruent. |
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| As PN is parallel to AB |
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| PA| is common |
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| these Ds are congruent. |
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| NA| = PD| |
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| DP + PD| = BN + NA| = BA| |
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| A|B| is the true reflected wave front. |
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| Further the wavefronts incident and reflected are perpendicular to the plane of paper as rays lie in the plane of paper. |
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