Q. Given below are two statements :

Statement I : A plane wave after passing through prism remains as plane wave but passing through small pin hole may become spherical wave.

Statement II : The curvature of a spherical wave emerging from a slit will increase for increasing slit width.

In the light of the above statements, choose the correct answer from the options given below :

(A) Both Statement I and Statement II are false

(B) Both Statement I and Statement II are true

(C) Statement I is true but Statement II is false

(D) Statement I is false but Statement II is true

Correct Answer: Statement I is true but Statement II is false

Explanation

A prism only deviates the direction of propagation of light. It does not change the nature of the wavefront. Therefore, a plane wave remains a plane wave even after passing through a prism.

When a plane wave passes through a very small pin hole, the pin hole acts as a point source. Due to diffraction, the emerging wavefront becomes spherical. Hence, Statement I is true.

For a slit of larger width, the wavefront emerging from it becomes less curved and tends to become a plane wave. Therefore, the curvature of the spherical wave actually decreases with increasing slit width.

Hence, Statement II is false.

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