In an experiment to determine the focal length of a concave mirror,the object distance is $x$ and the image distance is $y$,both measured from the pole of the mirror. Which of the following graphs correctly represents the relationship between $y$ and $x$?

The camera lens has an aperture of $f$ and the exposure time is $(1/60) \, s$. What will be the new exposure time if the aperture becomes $1.4 \, f$?

The figure shows a glowing mercury tube. The illuminances at points $A$, $B$, and $C$ are related as

An electric lamp is fixed at the ceiling of a circular tunnel as shown in the figure. What is the ratio of the intensities of light at base $A$ and a point $B$ on the wall?

If the focal length of the objective lens is increased,then:

$A$ small object is placed $50 \ cm$ to the left of a thin convex lens of focal length $30 \ cm$. $A$ convex spherical mirror of radius of curvature $100 \ cm$ is placed to the right of the lens at a distance of $50 \ cm$. The mirror is tilted such that the axis of the mirror is at an angle $\theta=30^{\circ}$ to the axis of the lens,as shown in the figure. If the origin of the coordinate system is taken to be at the centre of the lens,the coordinates (in $cm$) of the point $(x, y)$ at which the image is formed are