The Effective Resistance of resistors connected in Parallel

In parallel connection, the resistors are connected as shown below:

 In such a case, the total or effective resistance between terminals A and B is given by:

1/Rab = 1/R1 + 1/R2 + 1/R3

i.e. the reciprocal of the effective resistance is equal to sum of the reciprocals of the individual resistances.

If there are only two resistors, the above formula reduces to:

Rab = (R1*R2) / ( R1+ R2) 

e.g., if two 1K resistors are connected in parallel, the effective resistance is (1*1)/(1+1)= 1/2 = 0.5K=500 ohm.

In Parallel circuit, the Voltage that pass through each resistor is the same.

V1 = V2 = V3

Reference: http://www.electronic-circuits-diagrams.com/tutorials/resistors.shtml