In order to measure the internal resistance r₁ of a cell of emf E, a meter bridge of wire resistance R₀ = 50$$\Omega$$, a resistance R₀/2, another cell of emf E/2 (internal resistance r) and a galvanometer G are used in a circuit, as shown in the figure. If the null point is found at l = 72 cm, then the value of r₁ = __________ $$\Omega$$.

In the balanced condition, the values of the resistances of the four arms of a Wheatstone bridge are shown in the figure below. The resistance R₃ has temperature coefficient 0.0004$$^\circ$$C^-1. If the temperature of R₃ is increased by 100$$^\circ$$C, the voltage developed between S and T will be ________ volt.

In the following circuit, the current through the resistor R(=2$$\Omega$$) is I amperes. The value of I is :

A galvanometer gives full scale deflection with 0.006 A current. By connecting it to a 4990 $$\Omega$$ resistance, it can be converted into a voltmeter of range 0-30V. If connected to a $${{2n} \over {249}}\Omega $$ resistance, it becomes an ammeter of range 0-1.5 A. The value of n is