Kirchoff's law

Kirchoff's law

Kirchoff's current law

"For any node of a circuit, the sum of the incoming current is equal to the sum of the outgoing current."

For node A,

I1 = I2 + I3
or, I1 +(-I2) + (-I3) = 0

For node B,

I2 + I3 = I1
or, I2 + I3 + (-I1) = 0
 

Kirchoff's voltage law (Mess law)

"For a closed circuit the algebraic sum of E.M.F of the voltage source and the voltage drop in the resistance are equal to zero."

V1 = IR1
V2 = IR2
V3 = IR3
Applying Kirchoff's voltage low,
V = V1 + V2 + V3
V + (-V1) + (-V2) + (-V3) = 0

Sign Convention or Kirchoff's voltage law

1. Mark (+) sign to a end of resistance from which the assumed direction of current enters and mark (-)ve sign to the end of the resistance from which the assumed direction of current leaves.

2. The potential difference measured from (-)ve to (+)ve is called rise in voltage or positive voltage drop mark it (+)ve sign, and the potential difference measured from (+)ve to (-)ve is called fall in voltage or (-) ve voltage drop. Then, mark it (-)ve sign.

3. Mark (+) sign or (-)sign for source E.M.F as specified.