Two polaroids are oriented with their planes perpendicular to incident light and transmission axis making an angle $30^{\circ}$ with each other. What fraction of incident unpolarised light is transmitted?

$$ \left(\cos 30^{\circ}=\sqrt{3} / 2\right) $$

The acceleration (a) - time (T) graph for the body starting from rest is given below. The maximum speed of the body is

Two spherical black bodies have radii ' $R_1$ ' and ' $R_2$ '. Their surface temperatures are $T_1 K$ and $T_2 K$ respectively. If they radiate the same power, the ratio $\frac{R_1}{R_2}$ is

A thermometer bulb has volume $10^{-6} \mathrm{~m}^3$ and cross-section of the stem is $0.002 \mathrm{~cm}^2$. The bulb is filled with mercury at $0^{\circ} \mathrm{C}$. If the thermometer reads temperature as $100^{\circ} \mathrm{C}$, then the length of mercury column is (coefficient of cubical expansion of mercury $=18 \times 10^{-5} /{ }^{\circ} \mathrm{C}$ )