Hawkins Electrical Guide v. 01 (of 10) / Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications

by N. Hawkins

¹¹⁰⁄₁.8 = 61.11 amperes.

giving for each lamp a current of

¹¹⁰⁄₁₈₀ = .61 ampere.

In the case of two branches only, the following rule may be applied also:

Multiply the two resistances and divide the product by their sum.

Written as a formula:

Joint resistance = (R × R′)/(R + R′)

Again, assuming that R = 10 ohms and R′ = 20 ohms:

Joint resistance (10 × 20)/(10 + 20) = ²⁰⁰⁄₃₀ = 6²⁄₃ ohms.

This rule cannot be employed for more than two branches at a time.