A long conducting wire having a current $I$ flowing through it, is bent into a circular coil of $N$ turns. Then it is bent into a circular coil of $n$ turns. The magnetic field is calculated at the centre of coils in both the cases. The ratio of the magnetic field in first case to that of second case is:

Find the magnetic field at the point P in figure. The curved portion is a semicircle connected to two long straight wires.

As shown in the figure, a long straight conductor with semicircular arc of radius $\frac{\mathrm{\pi }}{10} m$ is carrying current $I = 3A$. The magnitude of the magnetic field. at the center $O$ of the arc is: (The permeability of the vacuum $= 4\mathrm{\pi }\times {10}^{-7}{\mathrm{NA}}^{-2}$ )

Given below are two statements : One is labelled as Assertion A and the other is labelled as Reason R.

Assertion A : For measuring the potential difference across a resistance of $600 \mathrm{\Omega }$, the voltmeter with resistance $1000 \mathrm{\Omega }$ will be preferred over voltmeter with resistance $4000 \mathrm{\Omega }$.

Reason R : Voltmeter with higher resistance will draw smaller current than voltmeter with lower resistance.

In the light of the above statements, choose the most appropriate answer from the options given below