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Why is it incorrect to simply add all currents at a junction as positive quantities and set them equal to zero?
ABecause current cannot be measured at a junction
BBecause currents have direction, so a sign convention is required in an algebraic sum
CBecause KCL applies only when all branch currents are equal
DBecause only DC circuits satisfy KCL
Answer & Solution
Correct answer: B. Because currents have direction, so a sign convention is required in an algebraic sum
An algebraic sum must account for direction. At a node, some currents enter and others leave, so one group must be assigned a positive sign and the other a negative sign. Otherwise the equation loses the meaning of conservation of charge.