Sunday, September 16, 2012

Kirchoff's Law

Kirchhoff’s Laws




Kirchhoff's first law
This law is also known as junction rule of current law (KCL). According to it the algebraic sum of current meeting at a junction is zero i.e. ∑i = 0.
Kirchoff's first law
In a circuit, at any junction the sum of the currents entering the junction must equal the sum of the currents leaving the junction. i1 + i3= i2 + i4
This law is simply a statement of "conservation of charge".
Kirchhoff second law: This law is also known as loop rule or voltage law (KVL) and according to it "the algebraic sum of the changes in potential in complete traversal of a mesh (closed loop) is zero", i.e. ∑V = 0
(i) This law represents "law of conservation of energy".
(ii) If there n meshes in a circuit, the number of independent equations in accordance with loop rule will be (n –1).



Sign convention for Kirchhoff's law: For the application of Kirchhoff's laws following sign convention are to be considered
(i) The change in potential in traversing a resistance in the direction of current is –iR while in the opposite direction + iR
Sign convention
(ii) The change in potential in traversing an emf source from negative to positive terminal is +E while in the opposite direction –E irrespective of the direction of current in the circuit.
(iii) The change in potential in traversing a capacitor from the negative plate to the positive plate is + q/C while in opposite direction – .
(iv) The change in voltage in traversing an inductor in the direction of current is –L dl/dt while in opposite direction it is +L dl/dt.
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