Question

Derive & expresion for current flowing
circut when an extranal resistance is canected
to real e.m.f dirise.
​

Answer 1

Answer:



ANSWER

Parallel combination of cells: In this combination the positive plates of all the cells are connected together at a point and the their negative plates are connected at another point and a suitable resistance is connected between these two points.

Expression for the current in the external circuit: Let m cells be connected in parallel combination as shown in Fig. The internal resistance of each cell is r and the e.m.f. of each cell is E. The resistance of the external circuit is R.

If the equivalent internal resistance of the combination is X then

X1=r1+r1+r1+........upon m terms

or X1=rm

or X=mr

Total resistance of the circuit =mr+R

Since the cells are connected in parallel thus the total e.m.f. of the circuit will be equal to the e.m.f. E of a single cell.

Thus, current in the circuit, I=TotalresistanceTotale.m.f.=mr+RE

or I=r+mRmE

This is the required expression.

Advantageous combination- If r>>mR, then mR is considered negligible.

I=rmE

or I=m×current obtained from one cell

Thus, this combination is advantageous when the internal resistance (r) of the cells is high, because the current obtained from a single cell becomes m times. In brief, the parallel combination of cells advantageous only when the internal resistance of cell is very large as compared to the external circuit.