Using Ampere's circuital law, find a magnetic field inside a current-carrying cylinder. 

A toroid having a square cross-section, $5.00 \mathrm{cm}$ on a side, and an inner radius of $19.0 \mathrm{cm}$ has $460$ turns and carries a current of $0.400 \mathrm{A}$ . (It is made up of a square solenoid-instead of round one as in figure bent into a doughnut shape). What is the magnetic field inside the toroid at (a) the inner radius and

(b) the outer radius?

In a metal wire of mass $m=24.1 \mathrm{mg}$ can slide with negligible friction on two horizontal parallel rails separated by a distance $d=2.56 \mathrm{cm}$. The track lies in a vertical uniform magnetic field of magnitude $56.3 \mathrm{mT}$. At time $t=0$, device $\mathrm{G}$ is connected to the rails, producing a constant current $i=9.13 \mathrm{mA}$ in the wire and rails (even as the wire moves). At $t=61.1 \mathrm{ms}$, what is the wire’s speed?