Fraunhofer lines are produced by the absorption of light in

Match the corresponding entries of Column-$I$ with Column-$II$. (Where $m$ is the magnification produced by the mirror)

Let $a, b$ and $c$ be distinct and none of them is equal to $1$. If the lines $x+ay+a=0$,$bx+y+b=0$ and $cx+cy+1=0$ are concurrent,then the value of $\frac{a}{a-1}+\frac{b}{b-1}+\frac{c}{c-1}$ is

$A$ ball is projected from the ground with a velocity $V$ at an angle $\theta$ to the vertical. On its path,it makes an elastic collision with a vertical wall and returns to the ground. The total time of flight of the ball is:

Let $R$ and $S$ be two relations on a set $A$. Then which of the following statements is true?

The output current versus time curve of a rectifier is shown in the figure. The average value of output current in this case is