$A$ biconvex lens $(R_1 = R_2 = 30 \ cm)$ has a focal length equal to the focal length of a concave mirror. What is the radius of curvature of the concave mirror (in $cm$)? (Refractive index of the material of the lens $\mu = 1.6$)

$A$ 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:

Total flux produced by a source of $1 \ cd$ is

Shown in the figure is a convergent lens placed inside a cell filled with a liquid. The lens has a focal length of $+20\,cm$ when in air and its material has a refractive index of $1.50$. If the liquid has a refractive index of $1.60$,the focal length of the system is......$cm$.

The figure shows a ray incident at an angle $i = \pi / 3$. The plot shows the variation of $|r - i|$ versus $k = \frac{\mu_1}{\mu_2}$,where $r$ is the angle of refraction. Based on the graph,which of the following statements is correct?

Assertion : $A$ red object appears dark in the yellow light.
Reason : The red colour is scattered less.