Question

Define the term 'wave front of light'. A plane wave front AB propagating from denser medium (1) into a rarer medium (2) is incident on the surface P₁P₂ separating the two media as shown in fig.

Using Huygen's principle, draw the secondary wavelets and obtain the refracted wave front in the diagram.

Answer 1

Wave front is defined as the locus (line) or surface having points in the same phase of vibration.

Let point A of the wavefront strikes the surface at t = 0 while B at time t

\(\therefore \ \ BB' = V_1t\)

In the same time t the wave fronts origination from A will expand.

Taking A as the centre, we draw an arc of radius v₂ t and draw a tangent from \(B'\) on this arc.

This tangent plane \(A'B'\) represents refracted wave front.

 Here, v₁ is speed of light in medium (1)

and v₂ is speed of light in medium (2)