$A$ $25\,cm$ long solenoid has radius $2\,cm$ and $500$ total number of turns. It carries a current of $15\,A.$ If it is equivalent to a magnet of the same size and magnetization $\vec M$ (magnetic moment per unit volume),then $\left| {\vec M} \right|$ is

How can the magnetic field of a solenoid be increased for a given current?

The magnetic field at point $P$ in the given figure, due to a current $I$ flowing through a cylindrical conductor of radius $R$, is:

The ratio of the magnetic field inside a solenoid at an axial point well inside and at an axial end point is

$A$ uniform current is flowing along the length of an infinite, straight, thin, hollow cylinder of radius $R$. The magnetic field $B$ produced at a perpendicular distance $d$ from the axis of the cylinder is plotted in a graph. Which of the following figures looks like the plot?

$A$ coaxial cable consists of an inner wire of radius $a$ surrounded by an outer shell of inner and outer radii $b$ and $c$ respectively. The inner wire carries an electric current $i_o$,which is distributed uniformly across its cross-sectional area. The outer shell carries an equal current in the opposite direction,also distributed uniformly. What will be the ratio of the magnetic field at a distance $x$ from the axis when $(i)$ $x < a$ and $(ii)$ $a < x < b$?