Wavefront behavior after reflection/refraction – Rankers Physics

Huygen's Principal: Practice Problem & Solution

Assertion (A): If incident wavefront is plane, then after reflection or refraction the emerging wave front also must be plane. Reason (R): Wavefronts are in the direction of energy propagation by light.  
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Huygen's Principal. Understanding the underlying formula is key to arriving at the correct answer below:

Assertion (A) is true: A plane wavefront remains plane after reflection or refraction from plane/spherical surfaces. Reason (R) is false: Wavefronts are surfaces of constant phase and are perpendicular to the direction of energy propagation (rays). Hence, (A) is true, but (R) is false.

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