Which scientist discovered that an electric current can be produced using a magnetic field?

What does the direction of the thumb indicate in the right-hand thumb rule?

Give the factors on which the magnetic field produced by a current-carrying solenoid depends.

$A$ student performs an experiment to study the magnetic effect of current around a current-carrying straight conductor with the help of a magnetic compass.
He reports that:
$(i)$ the degree of deflection of the magnetic compass increases when the compass is moved away from the conductor.
$(ii)$ the degree of deflection of the magnetic compass increases when the current through the conductor is increased.
Which of the above observations of the student appears to be wrong and why?

At the centre of which of the following four circular rings has the maximum magnetic field while passing equal current through each of them?

$AB$ 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?