Black sphere of radius R radiates power P at certain temperature $T$. If the temperature is doubled, the radius gets doubled. Now the power radiated would be

A series LCR circuit is connected to an a.c. source of $230 \mathrm{~V}, 50 \mathrm{~Hz}$. The circuit contains resistance of $80 \Omega$ an inductor having inductive reactance $70 \Omega$ and a capacitor of capacitive reactance $130 \Omega$. The power factor of the circuit is $x$. The value of $x$ is

The time period of a simple pendulum inside a stationary lift is $\sqrt{3}$ second. When the lift moves upwards with an acceleration $g / 3$, the time period will be ( $\mathrm{g}=$ acceleration due to gravity)

When three inductors of same inductance ' $L$ ' are connected in series and ' I ' is the current passing through the circuit. The energy stored in the circuit is