$\frac{V \cdot s}{A \cdot m}$ is the unit of which physical quantity?

$A$ portion of a conductive wire is bent in the form of a semicircle of radius $r$ as shown in the figure. At the centre $O$ of the semicircle,the magnetic induction will be:

Consider a tightly wound $100$ turn coil of radius $10 \,cm$ carrying a current of $2 \,A$. The magnitude of the magnetic field at the centre of the coil is

$A$ current of $4 \ A$ is passed through a square loop of side $5 \ cm$ made of a uniform manganin wire as shown in the figure. The magnetic field at the centre of the loop is

$A$ regular polygon of $6$ sides is formed by bending a wire of length $4 \pi \text{ m}$. If an electric current of $4 \pi \sqrt{3} \text{ A}$ is flowing through the sides of the polygon,the magnetic field at the centre of the polygon would be $x \times 10^{-7} \text{ T}$. The value of $x$ is . . . . . . .

Give two different properties of a current-carrying coil and state Ampere's suggestion.