Four polaroids are placed such that the optic axis of each is inclined at an angle of $30^{\circ}$ the optic axis of the preceding one. If unpolarised light of intensity ' $\mathrm{I}_0$ ' falls on the first polaroid, the intensity of light transmitted from the fourth polaroid is $\left[\cos 30^{\circ}=\frac{\sqrt{3}}{2}\right]$

Two bodies A and B move in same straight line starting from same position. Body moves with constant velocity ' u ' and body B moves with constant acceleration ' $a$ '. When their velocities become equal, the distance between them is

The ratio of angular momentum of an electron in $\mathrm{n}^{\text {th }}$ orbit of hydrogen atom to the velocity of electron in $\mathrm{n}^{\text {th }}$ orbit is proportional to

An element $\overrightarrow{\Delta l}=\Delta \mathrm{xi}$ is placed at the origin and carries a current of 10 A . The magnitude of magnetic field on the Y axis at a distance of 0.5 m if $\Delta x=1 \mathrm{~cm}$ is $\left(\frac{\mu_0}{4 \pi}=10^{-7}\right.$ SI unit $)\left(\sin 90^{\circ}=1\right)$