$A$ straight wire carrying a current $10\, A$ is bent into a semicircular arc of radius $5\, cm.$ The magnitude of the magnetic field at the center is

$A$ long wire is bent into a circular coil of one turn and then into a circular coil of smaller radius having $n$ turns. If the same current passes in both the cases,the ratio of magnetic fields produced at the centre for one turn to that of $n$ turns is

Write the equation for the magnetic field of a current-carrying circular loop at: $(i)$ a point on the axis,and $(ii)$ a point on the plane of the loop at a distance $x$ from the center of the loop.

An equilateral triangle of side '$a$' carries a current '$i$'. What is the magnetic field at point '$P$' (a vertex of the triangle)?

Which of the following is a vector quantity?

Derive an expression for the force per unit length between two infinitely long straight parallel current-carrying wires. Hence,define one ampere $(A)$.