If the luminous intensity of a $100 \, W$ unidirectional bulb is $100 \, \text{candela}$, then the total luminous flux emitted from the bulb is ....... $lumen$.

When seen in green light,the saffron and green portions of our National Flag will appear to be

$A$ 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?

An object $O$ is placed in front of a small plane mirror $M_1$ and a large convex mirror $M_2$ of focal length $f$. The distance between $O$ and $M_1$ is $x$,and the distance between $M_1$ and $M_2$ is $y$. The images of $O$ formed by $M_1$ and $M_2$ coincide. The magnitude of $f$ is

$A$ small piece of wire bent into an $L$ shape with upright and horizontal portions of equal lengths,is placed with the horizontal portion along the axis of a concave mirror whose radius of curvature is $10 \, cm$. If the bend is $20 \, cm$ from the pole of the mirror,then the ratio of the lengths of the images of the upright and horizontal portions of the wire is:

For a concave mirror,if a real image is formed,the graph between $\frac{1}{u}$ and $\frac{1}{v}$ is of the form: