Two planets A and B have densities ' $\rho_1$ ', ' $\rho_2$ ' and have radii ' $r_1$ ', ' $r_2$ ', respectively. The ratio of acceleration due to gravity on $A$ to that of $B$ is

A rectangular black body of temperature $127^{\circ} \mathrm{C}$ has surface area $4 \mathrm{~cm} \times 2 \mathrm{~cm}$ and rate of radiation is E . If its temperature is increased by $400^{\circ} \mathrm{C}$ and surface area is reduced to half of the initial value then the rate of radiation is

The reactance of a capacitor is $\mathrm{X}_{\mathrm{C}}$. If the frequency and the capacitance are doubled, then the new reactance will be