Question

How can i apply the Kirchoffs law?

Answer 1

(i) Starting from the positive terminal of the battery having highest emf, distribute current at various

junctions in the circuit in accordance with ‘junction rule’. It is not always easy to correctly guess the

direction of current, no problem if one assumes the wrong direction.

(ii) After assuming current in each branch, we pick a point and begin to walk (mentally) around a

closed loop. As we traverse each resistor, capacitor, inductor or battery we must write down, the voltage

change for that element according to the above sign convention.

(iii) By applying KVL we get one equation but in order to solve the circuit we require as many equations

as there are unknowns. So we select the required number of loops and apply Kirchhoff’s voltage law across

each such loop.

(iv) After solving the set of simultaneous equations, we obtain the numerical values of the assumed

currents. If any of these values come out to be negative, it indicates that particular current is in the opposite

direction from the assumed one.

Answer 2

Each individual component in a circuit comes with its own current-voltage law. For resistors it’s called Ohm’s Law, v = i R. With just individual component laws there is not enough information to figure out voltages and currents. You need more info.

Kirchhoff’s Laws (KCL and KVL) represent the connectivity of a circuit. They place constraints on v and i. Example constraints: if two resistors are in series, their currents must be the same. If two elements are in parallel, their voltage must be the same.

With enough KCL and/or KVL equations, along with i-v equations for the components, you can find every current and every voltage in a circuit.