A wheatstone bridge is used to determine the value of unknown resistance X by adjusting the variable resistance Y as shown in the figure. For the most precise measurement of X, the resistance P and Q

In a potentiometer circuit a cell of EMF 1.5 V gives balance point at 36 cm length of wire. If another cell of EMF 2.5 V replaces the first cell, then at what length of the wire, the balance point occurs?

The effective resistance of a parallel connection that consists of four wires of equal length, equal area of cross-section and same material is 0.25$$\Omega$$. What will be the effective resistance if they are connected in series?

Column - I gives certain physical terms associated with flow of current through a metallic conductor. Column-II gives some mathematical relations involving electrical quantities. Match column-I and column-II with appropriate relations.

	Column - I		Column - II
(A)	Drift Velocity	(P)	$${m \over {n{e^2}p}}$$
(B)	Electrical Resistivity	(Q)	$$ne{\upsilon _d}$$
(C)	Relaxation Period	(R)	$${{eE} \over m}\tau $$
(D)	Current Density	(S)	$${E \over J}$$