Question

What is the effective resistance between the points A and D? A) 1.3 Ω B) 2.2 Ω C) 10 Ω D) 12 Ω

Answer 1

Answer:

B) 2.2 Ω

Explanation:

First of all, we should notice that the resistor placed between A and B is short-circuited. In fact, the current from point A will follow the wire above between A and C (which has zero resistance), so we can basically ignore the presence of the resistor between A and B, since it has no effect on the circuit.

Then, we can notice that the two resistors between CB and CD are in parallel to each other; therefore, their equivalent resistance is given by:

$\frac{1}{R}=\frac{1}{R_{BC}}+\frac{1}{R_{CD}}=\frac{1}{4.0 \Omega}+\frac{1}{5.0 \Omega}=\frac{9}{20 \Omega}\\R= \frac{20 \Omega}{9}=2.2 \Omega$