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

Solution Explained:

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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