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

# Parallel Connection of Resistors

## Introduction

When two resistors $$R_1$$ and $$R_2$$ are connected in parallel, effective resistance of the circuit becomes $$R_e=R_1R_2/(R_1+R_2)$$.

## Apparatus

Voltmeter, Ammeter, Power Supply, Resistors and Connecting Wires

## Procedure

Connect three resistors ($$R_1$$, $$R_2$$ and $$R_3$$), an ammeter, a cell and a plug key, as shown in figure. Close the key and note the ammeter reading. This gives the current $$i$$ in the circuit. Now, connect the ammeter in the branch of the circuit that has $$R_1$$ and note the reading. This gives the current $$i_1$$ through the branch. Similarly, place the ammeter in the branches containing $$R_2$$ and $$R_3$$, and measure the current $$i_2$$ and $$i_3$$ respectively. You will find that the current $$i$$ gets divided into the branches such that $$i=i_1+i_2+i_3$$.