When the current flowing in a circular coil is doubled and the number of turns of the coil in it is halved,the magnetic field at its centre will become

$A$ circular loop of radius $0.0157\,m$ carries a current of $2.0\,A$. The magnetic field at the centre of the loop is $(\mu_0 = 4\pi \times 10^{-7}\,T\cdot m/A)$.

Given below are two statements:
Statement $(I)$: When currents vary with time,Newton's third law is valid only if momentum carried by the electromagnetic field is taken into account.
Statement $(II)$: Ampere's circuital law does not depend on Biot-Savart's law.
In the light of the above statements,choose the correct answer from the options given below:

The dimensions of the ratio of magnetic flux $(\phi)$ and permeability $(\mu)$ are

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

$A$ current of $i$ ampere is flowing in an equilateral triangle of side $a$. The magnetic induction at the centroid will be