In Young’s double slit experiment, the intensity at centre of screen is I. If one of the slit is closed, the intensity at centre now will be

In Young’s double slit experiment the intensity at centre of screen is I. If one of the slit is closed the intensity at centre now will be(a) I(b) \(\frac{l}{3}\)(c) \(\frac{l}{4}\)(d) \(\frac{l}{2}\)

Answer is :  (c)  \(\frac{l}{4}\) If I 0 is the intensity after closing one slit, then it satisfies I 0  ∝ a 2 (where, a = amplitude of light wave) When both slits open, then intensity ∴ l ∝ (2a) 2 = 4a 2 ⇒ l 0 =  \(\frac{l}{4}\)