If $\vec{F}=(5 \hat{i}-10 \hat{j})$ and $\vec{r}=(4 \hat{i}-3 \hat{j})$, then the torque acting on the object will be

Two long parallel wires carrying currents 4 A and 3 A in opposite directions are placed at a distance of 5 cm from each other. A point P is at equidistance from both the wires such that the line joining the point P to the wires are perpendicular to each other. The magnitude of magnetic field at point $P$ is ( $\mu_0=$ permeability of free space $=4 \pi \times 10^{-7}$ SI unit)

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