VerifiedHint: To explain this statement, first, we describe the two Kirchhoff’s laws and find out which principle these two laws are based on. Kirchhoff’s laws are basically used to solve complex circuits because, in every circuit problem, it is not possible to use ohm’s law.
Complete step by step answer:
A German physicist, Gustav Kirchhoff, developed a set of rules. These two rules are,
i) Kirchhoff’s current or junction law (Rule)(KCL)
It states that the sum of all the currents entering any point or junction must be equal to the sum of all currents leaving that point junction. It is based on the law of conservation of charges.
i.e. $\sum I = 0$
Consider a point O in an electrical circuit. Let $I_1$, $I_3$ be the currents entering the point O and $I_2$, $I_4$, $I_5$ be the currents leaving the point O. Then, according to Kirchhoff’s first law,
$\begin{array}{l}
{I_1} + {I_3} = {I_2} + {I_4} + {I_5}\\
\\
{I_1} + {I_3} - {I_2} - {I_4} - {I_5} = 0\\
\\
\therefore \sum I = 0
\end{array}$
Thus current entering the point can be taken as positive while currents were leaving the point taken as negative. This shows that if the algebraic sum of the current meeting at any junction is equivalent to zero. Therefore no charge has been accumulated at any junction; thus, the charge is conserved, and hence KCL is based on the conservation of charge.
ii) Kirchhoff’s second law (voltage law) (KVL)
It states that the algebraic sum of all voltages, i.e., the potential differences across all elements and e.m.f’s of all source s in any closed electrical circuit, is zero. It is based on the law of conservation of energy. Because a circuit loop is a fast conducting path, then no energy is lost.
i.e. $\sum E + \sum \Delta V = 0$
When we were applying Kirchhoff’s second rule, the loop rule, must identify a closed-loop and decide in which direction to go around it, clockwise or counterclockwise. The loop was traversed in the same order as the current (clockwise).
When a resistor is propagating within the equivalent direction to the current, the present change in potential is −IR.
When a resistor is traversed in the direction opposite to the current, the change in potential is +IR.
When an e.m.f is traversed from – to + (the same direction it moves positive charge), the change in potential is +e.m.f.
When an emf is propagating from + to – (opposite to the direction it moves positive charge), the change in potential is – e.m.f.
Therefore the correct option is (D).
Note: KCL and KVL are also applicable for AC circuits, and also they can be used to analyze any electrical circuit. The computation of voltage and current of complex circuits can be done quickly. KCL is valid as long as the entire electric charge is constant within the circuit, and calculation of unknown current and voltages is easy or closed-loop circuits become manageable.
