Question

Two resistors of R Ω and 20 Ω are connected in parallel to get an effective resistance of 15 Ω. Find R.
1. 40
2. 60
3. 50
4. 30

Answer 1

Correct Answer - Option 2 : 60

The correct answer is 60.

Concept:

The effective resistance of resistors in parallel (Reffective) is:

\({{1\over R_{effective}}={{1\over R_{1}}+{1\over R_{2}}}}\)

Given:

R_effective= \(15\ \Omega\)

R₁= \(R\ \Omega\)

R₂= \(20\ \Omega\)

Calculation:

\({{1\over 15}={{1\over R}+{1\over 20}}}\)

\(20R= 300+15R\)

\(5R=300\)

∴\(R=60\ \Omega.\)