Two sound waves each of wavelength ' $\lambda$ ' and having the same amplitude ' $A$ ' from two source ' $\mathrm{S}_1$ ' and ' $\mathrm{S}_2$ ' interfere at a point P . If the path difference, $\mathrm{S}_2 \mathrm{P}-\mathrm{S}_1 \mathrm{P}=\lambda / 3$ then the amplitude of resultant wave at point ' P ' will be $\left[\cos \left(120^{\circ}\right)=-0.5\right]$

Sodium light $\left(\lambda=6 \times 10^{-7} \mathrm{~m}\right)$ is used to produce interference pattern. The observed fringe width is 0.12 mm . The angle between the two wave trains is

A plate of refractive index 1.6 is introduced in the path of light from one of the slits in Young's double slit experiment then

In Young's double slit experiment, the intensity of light at a point on the screen where the path difference is $\lambda$ is x units, $\lambda$ being the wavelength of light used. The intensity at a point where the path difference is $\frac{\lambda}{4}$ will be $\left(\cos 2 \pi=1, \cos \frac{\pi}{2}=0\right)$