A glass slab of thickness $6.0$ cm is placed on the piece of paper on which an inkdot is marked. By how much distance would an inkdot appear to be raised? The velocity of light in glass is $2 \times 10^8 \text{ ms}^{-1}$ and that in air is $3 \times 10^8 \text{ ms}^{-1}$.

In Young's double slit experiment, the wavelength of light used is $\lambda$. The intensity on the screen at a point for path difference '$\lambda$' is 'X'. The intensity at the point for path difference $\left(\dfrac{\lambda}{6}\right)$ is ($\cos 180^\circ = -1$, $\cos 30^\circ = \dfrac{\sqrt{3}}{2}$)

In a single slit diffraction pattern, the distance between the plane of the slit and the screen is $1.4$ m. The width of the slit is $0.66$ mm. The second maximum is formed at the distance of $2.8$ mm from the center of the screen. The wavelength of light used is

In Young's double slit experiment, for the $n^{\text{th}}$ dark fringe ($n = 1, 2, 3, \ldots$) the phase difference of the interfering waves in radian will be