Aug 11, 2019
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  1. Pre-Psychology

Question: in Circuit Y with switch C closed, the current through Resistor IV is measured. Switch D is then closed. How does the current through Resistor IV change?

Answer: Current will not change, despite the change in total resistance.

My thoughts: the current is splitting at the junction and total resistance looks to be decreasing so I thought Current would increase. Please help.


2+ Year Member
Dec 26, 2016
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  1. MD/PhD Student
This is a pretty tricky E+M question; my understanding is that MCAT has moved away from these sorts of circuit q, but alas.

The current stays the same because the potential difference between points E and F (sorry for the poor marking) remains the same (V). You're right that total resistance of both branches becomes lower raising the current going through both the inner and outer branch, but that increase in current is solely for the new outer branch. image_LI.jpg
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2+ Year Member
Aug 10, 2017
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  1. Medical Student
I agree that this is way beyond what the MCAT will test. Know how to do basic circuits, how to add resistance in series and parallel, same thing with capacitance. That's about it. Focus on AAMC practice questions for Physics and don't expect anything more than that. I think I had 5 total physics questions on my MCAT in May.


2+ Year Member
Dec 5, 2017
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  1. Pre-Medical
I beg to differ here. This is exactly the level of the MCAT. This question looks really intimidating at first, but the basic concept is pretty easy. That is exactly what I encountered on test day and on AAMC section banks and exams. I'll agree that insane calculations on circuits don't appear to be tested, but conceptual questions and overwhelming diagrams are exactly what I saw on both AAMC practice materials and on test day. Being able to recognize the difference between parallel and series pathways is what is being tested here, not something complicated.
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