When calculating parallel resistance, your answer will usually be in the form of a reciprocal as 1
______ Rtotal
parallel resistance.
If resistors are connected in parallel (Fig. 24.5b), the total resistance can be calculated from the sum of the reciprocals of the individual resistances.
______ Rtotal
Resistors in parallel 1
= 1
___ R1
+ 1
___ R2
+ 1
___ R3
+... Rtotal = total resistance (Ω), R1, R2, R3 , ... = individual resistances (Ω) H
FIG. 24.5b In resistors connected in parallel, the reciprocal of the total resistance equals the sum of the reciprocals of the individual resistances
Derivation of resistors in parallel Itotal = I1 + I2 + I3
______ Rtotal
From I = V Vtotal
=
______ Rtotal
= 1
__ R :
______ R1
___ R1
Vtotal +
______ R2
Divide by Vtotal: 1
+ 1
___ R2
+ 1 Vtotal +
___ R3
QUESTIONS AND ANSWERS
3. Compare the resistance of three 30 Ω resistors (i) in series and (ii) in parallel.
