Logical reasoning PrepTest 134 · Section 2 · Question 7

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Water Pipes — Inertia is important. When a pump is turned on, it takes a while for water to reach full speed. When turned off, it gradually slows.
Water Pipes:Inertia::Electrical Circuits:Inductance

Answer Anticipation:
For those with rusty SAT skills, that last line is representing an analogy/comparison between water pipes and electrical circuits. Normally, such a comparison would be drawn in an argument, and we'd need to line up the elements in order to see where it breaks down or is missing a piece.

Here, however, this is a Must Be True question, so instead of seeing what's missing and then addressing it, we should be drawing an inference based on lining up elements and seeing what we can infer.

Since the final line tells us that the effects in electrical circuits of inductance is similar to the effects in water pipes of inertia, we can essentially rewrite what we wrote about water pipes replacing the equivalent words to make our inference:
Inductance is important. When an electrical circuit is turned on, it takes a while for electricity to reach full speed. When turned off, it gradually slows.

It's unclear what "full speed" means for electricity, but let's head into the answer choices to find an answer that reflects this inference/comparison.

Answer Explanation:
This answer generalizes from the two "prongs" of the situation described about water pipes, applied to inductance/electrical circuits. In water pipes, inertia affected the speed of water flow, both when the pump was turned on and off. This answer states that inductance does the same to the rate of electrical current flow, which is supported by the statement that the effects in the two sides of the analogy are similar.

Key Takeaway:
No matter what question type you're in, you should line up the elements of analogies in order to see how they work and what elements are related.

Incorrect. The stimulus notes that inductance has similar effects to inertia, so inertia doesn't need to play any role in electrical currents.

Incorrect. This answer is just a mishmash of all the terms in the stimulus, but since analogies deal with separate situations, mashing them all together isn't supported.

Incorrect. There's no indication that water engineers try to minimize the effects of inertia, so there's no basis for thinking electrical engineers try to minimize inductance in circuits.

Incorrect. The stimulus notes that the water flow to decrease gradually, but that doesn't require that the pump continues to pump water—it could be water already in the pipe that's still flowing while slowing down.