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Questions
Using Huygen’s wave theory of light, show that the angle of incidence is equal to the angle of reflection. Draw a neat and labelled diagram.
Using Huygen’s wave theory and a labelled diagram, show that angle of reflection (r) is equal to angle of incidence (i).
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Solution
Consider a plane wave AB incident at an angle i on a reflecting surface MN. If v represents the speed of the wave in the medium and if T represents the time taken by the wavefront to advance from point B to C, then distance BC = vt.
In order to construct the reflected wavefront, a sphere of radius = vt is drawn from point A, as shown in the figure. Let CE represent the tangent plane drawn from the point C to this surface.
∴ AE = BC = vt
∠ABC = ∠CEA = 90°
Here, AC is common.
∴ ΔEAC ≅ ΔBAC
Hence i = r
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Wavefront means
Represent diagrammatically how the incident planar wavefronts of wavelength λ pass through an aperture of size d, when d is approximately equal to λ.
