How is a wavefront defined? Using Huygen's construction , draw a figure showing the propagation of a plane wave refracting at a plane surface separating two media. Hence verify Snell's law of refraction.

Explanation

### Step-by-Step Solution:

**Step 1: Define Wavefront**
A wavefront is defined as the locus of all points in a medium that are vibrating in the same phase of a wave. In simpler terms, it is an imaginary surface that connects all the points that are at the same stage of their oscillation.

**Step 2: Huygens' Principle**
According to Huygens' principle, every point on a wavefront can be considered as a source of secondary wavelets. The new wavefront at a later time can be constructed by drawing a tangent to these wavelets.

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