$A$ 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:

Mention two main points about light.

An optical arrangement consists of two concave mirrors $M_1$ and $M_2$,and a convex lens $L$ with a common principal axis,as shown in the figure. The focal length of $L$ is $10 \text{ cm}$. The radii of curvature of $M_1$ and $M_2$ are $20 \text{ cm}$ and $24 \text{ cm}$,respectively. The distance between $L$ and $M_2$ is $20 \text{ cm}$. $A$ point object $S$ is placed at the mid-point between $L$ and $M_2$ on the axis. When the distance between $L$ and $M_1$ is $n/7 \text{ cm}$,one of the images coincides with $S$. The value of $n$ is. . . .

$1\%$ of light of a source with luminous intensity $50 \,cd$ is incident on a circular surface of radius $10 \,cm$. The average illuminance of the surface is: (in $,lux$)

$A$ reflecting surface is represented by the equation $y = \frac{2L}{\pi} \sin \left( \frac{\pi x}{L} \right)$,$0 \leq x \leq L$. $A$ ray travelling horizontally becomes vertical after reflection. The coordinates of the point$(s)$ where this ray is incident is?