Mark the correct statement.

Which of the following statements is correct?

Two straight long conductors $AOB$ and $COD$ are perpendicular to each other and carry currents $i_1$ and $i_2$. The magnitude of the magnetic induction at a point $P$ at a distance $a$ from the point $O$ in a direction perpendicular to the plane $ACBD$ is

Which of the following statements is correct?

$A$ charge $q$ is accelerated through a potential difference $V$. It is then passed normally through a uniform magnetic field,where it moves in a circle of radius $r$. The potential difference required to move it in a circle of radius $2r$ is (in $V$)

The neutral temperature of a thermocouple is $350\,^{\circ}C$ when the cold junction is at $0\,^{\circ}C$. When the cold junction is immersed in a bath of $30\,^{\circ}C$,the inversion temperature is .............. $^{\circ}C$.