The figure shows the path of a proton that passes through two regions containing uniform magnetic fields of magnitude $B_1$ and $B_2.$ Its path in each region is a half circle. Then

A current / flows in a long straight wire with crosssection having the form of a thin quarter-ring of radius $R$ (see figure). The magnetic field $\overrightarrow{B}$ at point $O$ if the current flows out of the page is

A semicircular wire of radius $R$ carrying current $/$ is placed in a magnetic field as shown in the figure. On right hand side of  $yy\text{'}$ the magnetic field is $2B_0,$ outward and on the left hand side it is $B_0$ inward as shown. The magnetic force experience by the wire is

The magnetic field at the centre of dotted circle in the arrangement shown is

The magnetic field at point $P$ in the hollow cylindrical wire carrying a current $i$ shown in the figure at a distance $r$ from axis $(a<r<b)$ is given by (Taking current density to be uniform across its cross-section)

A long straight wire is kept along $x-$axis. It carries a current $i$ in the positive $x$-direction. A proton and an electron are placed at $(0, a, 0)$ and $(0, -a, 0)$ respectively. The proton is imparted an initial velocity $v$ along $+z$ axis and the electron is imparted an initial velocity $v$ along $+x$-axis. The magnetic forces experienced by the two particles at the instant are

In the plane of coil a uniform magnetic field $B$ exists. Torque on the current carrying coil of radius $R$ is