Question 9: Why
we use Kirchhoff’s law for circuit problems solution? Explain its rules for circuit solution by
giving proper example.
Answer
Most often we come across electric circuits which cannot be simplified as series or parallel combination circuits. In such circuits, either there are more than one emf sources or the resistors are connected in a complicated manner. Ohm’s law cannot be applied to such complicated circuits.
German Physicist, Gustar Robert Kirchhoff gave two laws applicable in such situations and the unknown quantities can be easily found out by the application of these laws.
Applying Kirchhoff’s law to practical circuits, we adopt the following rules as solving strategy.
-
- Assume the direction of current in each branch of the circuit (clock or anti-clock wise) and mark it on the diagram of the circuit.
- Assume the direction of current in each branch of the circuit (clock or anti-clock wise) and mark it on the diagram of the circuit.
-
- Start from any point of
the branch (or loop), go around a loop in the direction of current and add
the emfs and IR terms as come.
- Start from any point of
the branch (or loop), go around a loop in the direction of current and add
the emfs and IR terms as come.
-
- While going through the source in direction from – to +, take the emf positive and while going from + to -, take it negative.
- In the direction of the assumed current, the IR is negative, and in the direction opposite to the assumed current it is positive.
- Using Kirchhoff’s rules, obtain as many simultaneous equation as that of the unknown number of currents and resistances.
Solve the equations for unknown quantities.
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