Match List I with List II

	List I (Current configuration)		List II (Magnitude of Magnetic Field at point O)
A.		I.	$${B_0} = {{{\mu _0}I} \over {4\pi r}}[\pi + 2]$$
B.		II.	$${B_0} = {{{\mu _0}} \over {4 }}{I \over r}$$
C.		III.	$${B_0} = {{{\mu _0}I} \over {2\pi r}}[\pi - 1]$$
D.		IV.	$${B_0} = {{{\mu _0}I} \over {4\pi r}}[\pi + 1]$$

Choose the correct answer from the options given below :

A long solenoid is formed by winding 70 turns cm$$^{-1}$$. If 2.0 A current flows, then the magnetic field produced inside the solenoid is ____________ ($$\mu_0=4\pi\times10^{-7}$$ TmA$$^{-1}$$)

Two long straight wires P and Q carrying equal current 10A each were kept parallel to each other at 5 cm distance. Magnitude of magnetic force experienced by 10 cm length of wire P is F$$_1$$. If distance between wires is halved and currents on them are doubled, force F$$_2$$ on 10 cm length of wire P will be:

A circular loop of radius $$r$$ is carrying current I A. The ratio of magnetic field at the center of circular loop and at a distance r from the center of the loop on its axis is :