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Writer's picturekeshprad

Barron's 2nd Edition DT Q49


49) This problem asks us to find the current flowing through the battery when the switch is open. The calculations and big idea for this problem are simple. However, usually, when someone gets this wrong, it is because they don't know what to do when the switch is open; they are unsure what to do with resistor R[3].


When the switch is open, we can imagine as if that parallel doesn't exist. Instead, we can just take the resistors R[1] and R[2].

Where R is resistance

After redrawing the system, it is easy to see that the resistance is in series. We can now use Ohm's law to solve for the current flowing through the battery.

Where V is voltage, I is current, and R is resistance

Answer: B

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