$AB$ is a current-carrying conductor in the plane of the paper as shown in the figure. What are the directions of the magnetic fields produced by it at points $P$ and $Q$? Given $r_1 > r_2$, where will the strength of the magnetic field be larger?

(N/A) According to the Right-Hand Thumb Rule, if you hold the current-carrying conductor in your right hand such that your thumb points in the direction of the current, your fingers will curl in the direction of the magnetic field lines.
For the given conductor with current flowing upwards, the magnetic field lines at point $P$ (to the right) go into the plane of the paper, and at point $Q$ (to the left), they come out of the plane of the paper.
The strength of the magnetic field produced by a straight current-carrying conductor is inversely proportional to the distance from the conductor $(B \propto 1/r)$.
Since $r_1 > r_2$, the point $Q$ is closer to the conductor than point $P$.
Therefore, the strength of the magnetic field will be larger at point $Q$.