CBSE NOTES CLASS 12 PHYSICS
CHAPTER 10 WAVE OPTICS
Behaviour of a plane wave front with different surfaces
Refraction through a prism: Since the speed of light waves is less in glass, the lower portion of the incoming wave front (which travels through the greatest thickness of glass) will get delayed resulting in a tilt in the emerging wave front.
Refraction through a lens: In case of a plane wave incident on a thin convex lens; the central part of the incident plane wave traverses the thickest portion of the lens and is delayed the most. The emerging wave front has a depression at the centre and therefore the wave front becomes spherical and converges to the point F which is known as the focus.
Reflection at a mirror: When a plane wave is incident on a concave mirror; on reflection we have a spherical wave converging to the focal point F.
In a similar manner, we can understand refraction and reflection by concave lenses and convex mirrors.