Getting your Trinity Audio player ready...

Hold down the T key for 3 seconds to activate the audio accessibility mode, at which point you can click the K key to pause and resume audio. Useful for the Check Your Understanding and See Answers.

Which One Doesn't Belong? - Equivalent Resistance - help6

When two or more resistors are placed in a circuit, it is common to describe their combined effect by comparing them to the effect of a single resistor. The equivalent resistance of such a circuit is the resistance that a single resistor would have in order to match the combined effect of all the resistors in that circuit. For instance, suppose that a series circuit having an equivalent resistance of 15 Ω were compared to a circuit with a single resistor having a resistance of 15 Ω; the two circuits would be equivalent to one another in terms of their effect upon the electric current.

There are three similar versions of this question. Here is one of the versions:

Version 1:

One of these circuits has an equivalent resistance that is not like the others. Which one doesn't belong?

Equivalent Resistance in a Series Circuit
When there are two or more resistors wired together in a series arrangement, the overall resistance to charge flow is greater than the resistance of each of the individual resistors. As discussed in the Fundamentals section (above), the equivalent resistance of such a circuit is the resistance that a single resistor would have in order to match the combined effect of all the resistors in that circuit. For series circuits, the equivalent resistance is simply the sum of the resistance values of the individual resistors. So having three 5-Ω resistors would be equivalent to having a single 15-Ω resistor.

Try this link to The Physics Classroom Tutorial for more help with the equivalent resistance in a series circuit:

Series Circuits