$A$ ray of light enters from air into water. Which of the following figures shows the dispersion of light?

$A$ light source is located at $P_1$ as shown in the figure. All sides of the polygon are equal. The intensity of illumination at $P_2$ is $I_0$. What will be the intensity of illumination at $P_3$?

$A$ concave mirror and a converging lens (glass with $\mu = 1.5$) both have a focal length of $3 \, cm$ when in air. When they are in water $\left( \mu = \frac{4}{3} \right)$,what are their new focal lengths?

$A$ light ray is incident,at an incident angle $\theta_{1}$,on the system of two plane mirrors $M_{1}$ and $M_{2}$ having an inclination angle $75^{\circ}$ between them (as shown in figure). After reflecting from mirror $M_{1}$,it gets reflected back by the mirror $M_{2}$ with an angle of reflection $30^{\circ}$. The total deviation of the ray will be $\dots$ degree.

$A$ point object is placed at a distance of $60\, cm$ from a convex lens of focal length $30\, cm$. If a plane mirror is placed perpendicular to the principal axis of the lens at a distance of $40\, cm$ from it,the final image is formed at a distance of:

Which of the following statements is correct?