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In applying Kirchhoff's Voltage Law to a loop, why is it important to keep track of polarity signs across circuit elements as shown in the figure? 
ABecause voltage has magnitude but no direction-related sign
BBecause the algebraic sum depends on whether each element is crossed as a rise or a drop
CBecause polarity matters only for resistors, not for sources
DBecause loop equations are independent of traversal direction
Answer & Solution
Correct answer: B. Because the algebraic sum depends on whether each element is crossed as a rise or a drop
KVL uses an algebraic sum, so the sign of each term matters. Depending on the direction you traverse the loop and the marked polarity of an element, you count that element as a voltage rise or a voltage drop. Ignoring polarity leads to incorrect loop equations.
