Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Series Connection of Resistors

Introduction

When two resistors \(R_1\) and \(R_2\) are connected in series, effective resistance of the circuit becomes \(R_e=R_1+R_2\).

Apparatus

Voltmeter, Ammeter, Power Supply, Resistors and Connecting Wires

Procedure

qaa.png

You can use different kind of bulbs as resistors in this activity. Connect three resistors of resistances \(R_1\), \(R_2\) and \(R_3\) to an ammeter, a cell and a plug key, as shown in figure. The three resistors are connected in series. Close the key and note the ammeter reading. Now connect the ammeter between \(R_1\) and \(R_2\) and note the reading. Similarly, place the ammeter between the other circuit elements and measure the current. You will find that the value of the current is the same everywhere in the circuit. So, the same current passes through the three resistors.

Now, connect a voltmeter in the circuit, as shown in figure. Close the key and note the potential difference \(V\) across the series combination of resistors. Then connect the voltmeter across \(R_1\) and note the reading \(V_1\). Similarly, connect the voltmeter across \(R_2\) and \(R_3\), one at a time, and measure the potential difference \(V_2\) and \(V_3\) across them. You will find that \(V=V_1+V_2+V_3\).