The magnetic effect of current was discovered by

An electric current is flowing through a circular coil of radius $R$. The ratio of the magnetic field at the centre of the coil and that at a distance $2\sqrt{2}R$ from the centre of the coil on its axis is:

Two concentric circular coils $A$ and $B$ have radii $20 \text{ cm}$ and $10 \text{ cm}$ respectively and lie in the same plane. The current in coil $A$ is $0.5 \text{ A}$ in the anticlockwise direction. What is the current in coil $B$ such that the net magnetic field at the common centre is zero?

The ratio of the magnetic field at the center of a current-carrying circular coil of radius $R$ to the magnetic field at a distance of $3R$ from the center on its axis is:

The figure shows a current-carrying square loop $\text{ABCD}$ of edge length '$a$' lying in a plane. If the resistance of the $\text{ABC}$ part is $r$ and that of the $\text{ADC}$ part is $2r$,then the magnitude of the resultant magnetic field at the centre of the square loop is:

Two mutually perpendicular insulated conducting wires carrying equal currents $I$ intersect at the origin. The resultant magnetic induction at point $P(2 \ m, 3 \ m)$ will be: