question 29

[mvenus929]

Ok, I understand the concepts of constructive and destructive interference, but please tell me how you can vary amplitudes between 4 and 12 for each ray, and end up with 8 and 4 as the possible products. Or 12 and 4 as possible products. It should be 16 and 8, shouldn't it be?

I think that this question has the values in the question and the values in the answer mixed up. It explains that the range is 12 and 4 in the answer, even though it marks this answer as incorrect, and this isn't even a possible range.

[eo5]

The range is 4-12..

If constructive interference then 8amp + 4amp =12
If destructive interference then 8amp - 4 amp= 4
The question is asking the possible amplitude of each waves before it goes thru the interference....
I hope that helps!

[admin]

eo5 has it. The values in the explanation are correct. The explanation is repeating the data from the question which is that the range is between 4 and 12. How can we possibly take 2 numbers to add (constructive interference) and get 12 or subtract to get 4 (destructive interference)?

Answer: choose 8 and 4

I would say that every 3rd MCAT has an independent question like this one.

[student]

I think this question is badly worded. In order for constructive or destructive interference to occur, shouldn't the two waves have to pass through the same region of space at the same time?

in this question, it just says that two waves pass through the same medium, which means they could be waves that are far apart from each other but still in the same medium.

when i looked at this question, i didn't even think of interference because of the way it was worded. i just thought it meant what the maximum amplitude of each wave (and thus I got confused really quickly!)

[admin]

Very good point!

Have you ever felt that way in a real exam? An ambiguous question that seems unfair? Unfortunately, that happens from time to time with the MCAT. A minority of questions may not even explicitly state an assumption that is necessary to solve the problem.

We would not be doing our jobs if we don't represent fully what you will see on the real test.

The bottom line for practicing is "pattern recognition." If you practice with all the AAMC's questions, you will find a very similar problem to this one a few times. If you see it on the test that counts, you won't be confused, hopefully you'll just smile, put the right answer within seconds and move on.