1. Locus of all points having same phase of vibration is called wavefront.

2. Spherical wavefront, cylindrical wavefront plane wave front

**3. Wave frond through a thin convex lens:**

Consider a plane wave passing through a thin convex lens. The central part of the incident plane wave travels through the thickest portion of lens. Hence central part get delayed. As a result the emerging wave frond has a depression at the centre. Therefore the wave front becomes spherical and converges to a point F.