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

**KIRCHHOFF’S RULES**

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

**Kirchhoff’s 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

I_{1}
+ I_{2}–I_{3} – I_{4} – I_{5} = 0

(or)

I_{1} + I_{2} = I_{3} + I_{4} + I_{5}

**EXAMPLE 2.20**

From the given circuit
find the value of I.

**Solution**

Applying Kirchoff’s rule
to the point P in the circuit,

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

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

1.5A – 0.9A – I = 0

0.6A – I = 0

I = 0.6 A

Tags : Explanation, Formulas, Solved Example Problems , 12th Physics : Current Electricity

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

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