A student performs an experiment for determination of $g\left(=\frac{4 \pi^2 l}{\mathrm{~T}^2}\right), l=1 m$, and he commits an error of $\Delta l$. For T , he takes the time of $n$ oscillations with the stop watch of least count $\Delta \mathrm{T}$ and he commits a human error of 0.1 s . For which of the following data, the measurement of $g$ will be most accurate?

In a screw gauge, the zero of main scale coincides with the fifth division of circular scale in figure (i).The circular division of screw gauge is 50. It moves 0.5 mm on main scale in one rotation.The diameter of the ball in figure (ii) is

Match the following columns.

	Column I		Column II
(A)	Dielectric ring uniformly charged.	(P)	Time independent electrostatic field out of system.
(B)	Dielectric ring uniformly charged rotating with angular velocity $$\omega$$.	(Q)	Magnetic field.
(C)	Constant current in ring $$io$$	(R)	Induced electric field.
(D)	$$i=i_0\cos\omega t$$	(S)	Magnetic moment.

A solid sphere of radius $R$ has moment of inertia $I$ about its geometrical axis. If it is melted into a disc of radius $r$ and thickness $t$. If its moment of inertia about the tangential axis (which is perpendicular to plane of the disc), is also equal to $I$, then the value of $r$ is equal to