A cylindrical conductor AB of non-uniform area of cross-section carries a current of 5A. The radius of the conductor at one end A is 0.5 cm. The current density at the other end of the conductor is half of the value at A. The radius of the conductor at the end B is nearly

The effective resistance between p and q in given figure is

Two batteries, one of emf $$18 \mathrm{~V}$$ and internal resistance $$2 \Omega$$ and the other of emf $$12 \mathrm{~V}$$ and internal resistance $$1 \Omega$$ are connected as shown. The voltmeter $$V$$ will record a reading of

Assertion : A potentiometer is preferred over that of a voltmeter for measurement of emf of a cell.

Reason : Potentiometer does not draw any current from the cell.