A coil of effective area $3 \mathrm{~m}^2$ is placed at right angles to a magnetic field of induction $0.05 \mathrm{~Wb} / \mathrm{m}^2$ If the field is decreased to $20 \%$ of its original value in 10 second, the e.m.f. induced in the coil will be

Two vectors $a \hat{i}+b \hat{j}+\hat{k}$ and $2 \hat{i}-3 \hat{j}+4 \hat{k}$ are perpendicular to each other. When $3 \mathrm{a}+2 \mathrm{~b}=7$, the ratio of $a$ to $b$ is $\frac{x}{2}$. The value of $x$ is

Three immiscible transparent liquids with refractive indices $3 / 2,4 / 3$ and $6 / 5$ are arranged one above the other in a container. The depths of the liquids are $3 \mathrm{~cm}, 4 \mathrm{~cm}$ and 6 cm respectively. The apparent depth of the vessel is

A spherical liquid drop splits in to 729 identical spherical drops. If $E$ is the surface energy of the original drop and $U$ is the total surface energy of resulting drops, then $\frac{E}{U}=\frac{1}{x}$. The value of $x$ is