In the half-wave rectifier circuit shown,which one of the following waveforms is true for $V_{CD}$,the output across $C$ and $D$?

$A$ uniform but time-varying magnetic field $B(t)$ exists in a circular region of radius $a$ and is directed into the plane of the paper,as shown. The magnitude of the induced electric field at point $P$ at a distance $r$ $(r > a)$ from the centre of the circular region:

If $P=(0,1,2)$,$Q=(4,-2,1)$,and $O=(0,0,0)$,then $\angle POQ$ is equal to

Which of the following has the lowest boiling point?

In a compound,$C$,$H$,and $N$ atoms are present in the ratio $9 : 1 : 3.5$ by weight. The molecular weight of the compound is $108$. Its molecular formula is:

As shown in the figure,a block of mass $10 \, kg$ lying on a horizontal surface is pulled by a force $F$ acting at an angle of $30^{\circ}$ with the horizontal. For $\mu_{s} = 0.25$,the block will just start to move for the value of $F$ in $N$ is: [Given $g = 10 \, ms^{-2}$]