HELP: AAMC sample test CP #37 (spoiler)

[quickaskz]

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so i understand that when voltage is held constant, and we can see from the table that resistance increases therefore current should decrease. But why don't we use the values that current is increasing from the table? also where does the initial 4.6A come from?

 

[parkerr]

Did you ever get the answer to this? I was wondering this as well.

 

[Premed2295]

The table shows trials 1-5. The question is not directly based on the table but rather extracting data from what happened during trial 5. The length and voltage change across trials so the chart is not relevant for this question.

The “real” question is what happens to resistance, and therefore current as you heat a wire. Answer, resistance increases currents decreases.

 

[parkerr]

The table shows trials 1-5. The question is not directly based on the table but rather extracting data from what happened during trial 5. The length and voltage change across trials so the chart is not relevant for this question.

The “real” question is what happens to resistance, and therefore current as you heat a wire. Answer, resistance increases currents decreases.

So are you just supposed to know that heating a wire increases resistance? Or was I supposed to gather that from the passage?

 

[ThrowawayShmoaway]

So are you just supposed to know that heating a wire increases resistance? Or was I supposed to gather that from the passage?

It's a reasoning question. From the table, you can see that as the temperature in each sucessive trial increases, the length of the wire slightly increases, as well. You're supposed to already know that as length increases, so does resistance. And that as resistance increases, current decreases.
Therefore, D is the only answer that would make sense if the resistance is increasing, because it's the only answer where the current is changing (automatically ruling out answers A & B) and decreasing (ruling out answer C). No calculations were necessary.

 

[parkerr]

It's a reasoning question. From the table, you can see that as the temperature in each sucessive trial increases, the length of the wire slightly increases, as well. You're supposed to already know that as length increases, so does resistance. And that as resistance increases, current decreases.
Therefore, D is the only answer that would make sense if the resistance is increasing, because it's the only answer where the current is changing (automatically ruling out answers A & B) and decreasing (ruling out answer C). No calculations were necessary.

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Thank you so much this makes so much more sense now! I didn't get the correlation between resistance and length, but it's literally in the sentence after the table lol. So as temp increases, length is also shown to increase, which would increase resistance. If V is constant, current would have to decrease as a result of the increasing resistance in the wire?

 

[ThrowawayShmoaway]

If V is constant, current would have to decrease as a result of the increasing resistance in the wire?

Correct, because of Ohm's law (see equation below) which shows that resistance and current have an inverse relationship when V is constant. I'm sure you already know Ohm's Law is a must-know for test day.

Also, my original reasoning in my first post could be shortened even more: I'm blind and didn't notice that the table also shows that the resistance increases with each trial as well (as the temp increase), so all you had to do was just compare Trial 1's resistance to Trial 5's, see that resistance is higher in the latter, then reason/process-of-elimination your way to answer D using the relationships in Ohm's Law.

 

[Premed2295]

So are you just supposed to know that heating a wire increases resistance? Or was I supposed to gather that from the passage?

As the last poster just said, you can extrapolate from the other given information or simply remember ohms law/ learning this in physics class. The MCAT does test prior knowledge but a lot of times if you forget something you can use logic to get out of that trouble