Explain the principle on which the working of a potentiometre is based. Why is the use of a potentiometer preferred over that of a voltmeter for measurement of e.m.f. of a cell?

Why is potentiometer preferred to voltmeter for the measurement of emf of a cell? Explain.

Why is potentiometer converted for the measurement of emf of a cell? Explain.

The internal resistance of a battery of e.m.f. 100 Vis 4 Omega . A voltmeter of resistance 250 Omega is used to measure the e.m.f. of the battery. What should be the minimum value of the voltmeter resistance so that the error in finding the e.m.f. of the battery may not be more than 1 percent?

In a potetiometer experiment why is ti necessary to use a long wire? Length and resistence of a potetiometer wire are 4m and 10Omega respectively. It is concerned to a cell of mef2 volt. Another cell when joined to this potntiometer and null point is meausred at 250 cm. Find out the emf of the second cell.