question_answer

(i) State Kirchhoff's rules for an electrical network.

(ii) The plot of the variation of potential difference across a combination of three identical cells in series, versus current is as shown below, What is the emf of each cell?

Answer:

(i) Kirchhoff's junction rule

In an electric circuit at any junction, the sum of the currents entering the junction is equal to the sum of currents leaving that junction.

Kirchhoff's loop rule

In an electric circuit, the algebraic sum of change in potential differences across the circuit elements of any closed loop is zero.

(ii) Consider the circuit consisting of 3 identical cells in series.

Let emf of each cell = E Let internal resistance of each cell = r, then \[V=(E+E+E)-i(r+r+r)=3(E-ir)\] From the graph, when i = 0, V = 6 i.e.        \[6=3(E-0)=3E\]             \[E=6/3\Rightarrow E=2\]