The magnetic field at center O of the arc in figure is :

Figure shows three cases, in all cases the circular part has radius r and stragiht ones are infinitely long. For the same current the ratio of field B at center P in the three cases B1 : B2 : B3 is :

Find out magnetic dipole moment of given current loop.

In figure, there is a uniform conducting structure in which each small square has side a. The
structure is kept in a uniform magnetic field B. Then the magnetic force on the structure will
be :

A straight section PQ of a circuit lies along the X-axis form x = –a/2 to x = a/2 and carries a steady current i. The magnetic field due to the section PQ at a point X = +a will be :

A long straight wire carrying a current of 30A is placed in an external uniform magnetic field
of induction \[4\times 10^{-4} T\]. The magnetic field is acting parallel to the direction of current. The magnitude of the resultant magnetic induction in tesla at a point 2.0 cm away from the wire is
\[\left( \mu_{0}=4\pi\times 10^{-7}H/m \right)\]:

Two parallel long wires carry currents i1 and i2 with i1 > i2. When the currents are in the same
direction, the magnetic field midway between the wires is 10μT. When the direction of i2 is reversed, it becomes 40μT. the ratio i1/i2 is :

The magnetic field at the centre of an equilateral triangular loop of side 2L and carrying a current i is :

Two wires AO and OC carry equal currents i as shown in figure. One end of both the wire extends to infinity. Angle AOC is α. The magnitude of magnetic field at a point P on the bisector of these two wires at a distance r from point O is :

Two very thin metallic wires placed along X and Y-axis carry equal currents as shown in figure. AB and CD are lines at 45º with the axes with origin of axes of O. The magnetic fields will be zero on the line :