The potential difference across a resistor ‘r’ carrying current ‘I’ is Ir. (i) Now if the potential difference across ‘r’ is measured using a voltmeter of resistance ‘$R_{v}$’, show that the reading of voltmeter is less than the true value. (ii) Find the percentage error in measuring the potential difference by a voltmeter. (iii) At what value of $R_{v}$’, does the voltmeter measures the true potential difference?

In the two electric circuits shown in the figure, determine the readings of ideal ammeter (A) and the ideal voltmeter (V).

(i) Derive an expression for drift velocity of electrons in a conductor. Hence deduce Ohm’s law. (ii) A wire whose cross-sectional area is increasing linearly from its one end to the other, is connected across a battery of V volts. Which of the following quantities remain constant in the wire ? (a) drift speed (b) current density (c) electric current (d) electric field Justify your answer.