In the circuit shown in the figure, the rheostat has a resistance of 30 . Assuming the resistance of the ammeter is negligible, calculate the minimum and maximum currents passing through the ammeter as the rheostat is varied.

Step-by-step solution

The equivalent resistance of the parallel combination of 10 and 20 resistors is: R_p = 10 20 10 + 20 = 200 30 = 20 3 The total resistance of the circuit is the sum of R_p and the resistance of the rheostat R_v included in the circuit: R_ eq = R_p + R_v = 20 3 + R_v The current in the circuit is given by Ohm's law: I = V R_ eq = 5.5 20 3 + R_v For maximum current, the rheostat resistance should be minimum, i.e., R_v = 0 : I_ max = 5.5 20 3 + 0 = 5.5 3 20 = 16.5 20 = 0.825 A 0.83 A For minimum current, the rheostat r