Fringe Width and Slit Separation – Rankers Physics
Topic: Wave Optics
Subtopic: Young's Double Slit Experiment

Fringe Width and Slit Separation

Assertion (A): As the separation between the two slits is increased width of fringes decreases.
Reason (R): On increasing separation between two slits, angular separation of fringes decreases.
 
(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
(2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(3) (A) is true but (R) is false
(4) Both (A) and (R) are false

Solution:

Fringe width \(beta = \frac{\lambda D}{d}\). As slit separation \(d\) increases, fringe width \(beta\) decreases. Angular fringe width \(theta = \frac{\lambda}{d}\). As \(d\) increases, angular separation \(\theta\) decreases. Thus, R is the correct explanation of A.

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