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# KirchhoffŌĆÖs first rule (Current rule or Junction rule)

It states that the algebraic sum of the currents at any junction of a circuit is zero.

KIRCHHOFFŌĆÖS RULES

OhmŌĆÖs law is useful only for simple circuits. For more complex circuits, KirchhoffŌĆÖs rules can be used to find current and voltage. There are two generalized rules: i) KirchhoffŌĆÖs current rule ii) KirchhoffŌĆÖs voltage rule.

KirchhoffŌĆÖs first rule (Current rule or Junction rule)

It states that the algebraic sum of the currents at any junction of a circuit is zero. It is a statement of conservation of electric charge. All charges that enter a given junction in a circuit must leave that junction since charge cannot build up or disappear at a junction. Current entering the junction is taken as positive and current leaving the junction is taken as negative. Applying this law to the junction A in Figure 2.23

I1 + I2ŌĆōI3 ŌĆō I4 ŌĆō I5 = 0

(or)

I1 + I2 = I3 + I4 + I5

EXAMPLE 2.20

From the given circuit find the value of I. Solution

Applying KirchoffŌĆÖs rule to the point P in the circuit,

The arrows pointing towards P are positive and away from P are negative.

Therefore, 0.2A ŌĆō 0.4A + 0.6A ŌĆō 0.5A + 0.7A ŌĆō I = 0

1.5A ŌĆō 0.9A ŌĆō I = 0

0.6A ŌĆō I = 0

I = 0.6 A

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12th Physics : Current Electricity : KirchhoffŌĆÖs first rule (Current rule or Junction rule) | Explanation, Formulas, Solved Example Problems