PrepTest 128, Section 3, Question 2
Because metallic mirrors absorb some light, they waste(40 more words not shown)
Which one of the following(7 more words not shown)
- AMetallic mirrors reduce(5 more words not shown)
- BPart of the(11 more words not shown)
- CHigh-powered lasers require(4 more words not shown)
- DA tendency to(10 more words not shown)
- EMetallic mirrors are(11 more words not shown)
Reading the argument
An energy-efficient mirror? At first I'm picturing a bathroom mirror and wondering why a slightly dimmer reflection matters. But the author eventually gets to high-powered lasers. Losing light energy could matter in that setting in a way it doesn't when I'm checking my reflection.
Follow the explanation: metallic mirrors absorb some light. Light makes electrons in the mirror move, which uses energy and leaves a dimmer reflected image. The author uses that loss to argue that metallic mirrors cannot be used where minimizing energy loss matters.
We could question how much energy is lost. Suppose a mirror loses 1 percent and a particular laser can tolerate a 10 percent loss. Merely saying that some energy is lost wouldn't settle whether that mirror is unsuitable. Those numbers are hypothetical; they show a question we'd want answered before accepting the argument completely.
What we’re looking for
But this question asks for the main conclusion, not an objection. What is the author trying to establish with the information about absorbed light and moving electrons? That metallic mirrors are unsuitable for certain applications. The scientific explanation supports that restriction on their use.
Working the answers
- A
This focuses on the effect on high-powered lasers. Lasers are an example of the applications the conclusion covers, but the conclusion is the broader restriction on using metallic mirrors wherever minimizing energy loss is important. A doesn't fully state that point.
- B
Absorbing some incoming light is a starting fact in the explanation. The author uses it to establish energy loss and then the restriction on applications. B gives us a reason for the conclusion, not the conclusion itself.
- C
The need to conserve energy explains why a high-powered laser is a relevant example. But the main point concerns which mirrors are unsuitable for such applications. C leaves out that judgment about metallic mirrors.
- D
The author never ranks the disadvantages of metallic mirrors. Perhaps they are fragile or unattractive, and some user cares more about that. The passage discusses energy loss without establishing that it is the most significant disadvantage.
- ECorrect
Being unsuitable for applications where minimizing energy loss is crucial restates the claim that metallic mirrors cannot be used in those applications. The absorption and electron movement are the reasons offered for this conclusion. We can identify that conclusion even while wondering how much energy loss an application would actually tolerate.
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