Identify the correct statement(s) among the following:

(A) The time taken by a light wave is $5 × 10^{-9} s$ to travel a thickness of 1 cm of glass having refractive index 1.5.
(B) Two similar waves of amplitude of 3 mm and 5 mm reach a point in the same phase. The resultant amplitude will be 8 mm.
(C) Two waves of amplitude 2 mm each reach a point with a phase difference of $π/2$. The resultant amplitude is zero.
(D) If, one of the slits is closed in Young's double slit experiment, the interference pattern will disappear.

Choose the correct answer from the options given below:-

(B) and (D) only

The correct answer is Option (3) → (B) and (D) only

(A) Correct — Time taken $t = \frac{nd}{c} = \frac{1.5 \times 0.01}{3 \times 10^{8}} = 5 \times 10^{-11}\,\text{s}$, not $5 \times 10^{-9}\,\text{s}$. So (A) is incorrect.

(B) Correct — If two waves of amplitudes $a_{1}=3$ mm and $a_{2}=5$ mm arrive in the same phase, resultant amplitude $=a_{1}+a_{2}=8$ mm.

(C) Incorrect — For amplitudes $a_{1}=a_{2}=2$ mm with phase difference $\pi/2$, resultant amplitude $= \sqrt{a_{1}^{2}+a_{2}^{2}}=\sqrt{4+4}=2\sqrt{2}$ mm $\neq 0$.

(D) Correct — With one slit closed, no interference occurs, only single-slit diffraction remains.

Final Answer: (B), (D)