Question

 Explain with the help of a labelled circuit diagram, how you will find the resistance of a combination of three resistors of resistances R₁, R₂ and R₃ joined in parallel.

Answer 1

  

Let the resistance of the three resistors be R₁, R₂ and R₃, respectively. Let their combined resistance be R. Let the total current flowing in the circuit be I and the strength of the battery be V.  Then from Ohm's law, we have:
V = IR       .....(1)
We know that when the resistors are connected in parallel, the potential drop across each resistance is the same.
Therefore:
I = I₁ + I₂ + I₃
I = V/R₁ + V/R₂ + V/R₃
I = V/(1/R₁ + 1/R₂ + 1/R₃) ...... (2)
From equations (1) and (2) we have:
1/R = 1/R₁ + 1/R₂ + 1/R₃