Explain with circuit diagram the parallel combination of identical cells. Obtain the condition for maximum current in the external resistance connected with the combination.

Considering m identical cells: C 1 , C 2 , ..., C m All the cells are having emf of E and internal resistance r and connected to an external resistance R parallelly. As per the arrangement of cells, the equivalent emf of all the cells is equal to emf of a single cell, that is, E e f f = E The equivalent resistance of all the cells: 1 r e f f = 1 r + 1 r + . . . + 1 r = m 1 r ⇒ r e f f = r m So the total resistance in the circuit: R n e t = r e f f + R = r m + R The current flowing through the circuit: I = E R n e t = E r m + R = m E r + m R If R < < r then we can neglect R in the above circuit then maximum current can be observed that will be I = m E r .

Define internal resistance of a cell. State two factors on which it depends.

Internal resistance of cell: The opposition offered by the electrolyte and electrode of a cell to the flow of current through it, is referred to be internal resistance of cell. Following are the factors on which internal resistance of cell depends: Size of the electrodes of the cell. Quantity of the electrolyte in a cell.

Describe with circuit diagram an experiment to compare the e.m.f. of two cells with the help of a potentiometer.

For comparing electromotive force of two cells using potentiometer: When switch s is connected to terminal 1 of the circuit: E 1 = V A J .......................... 1 According to the principle of the potentiometer: V A J α l 1 then V A J = k l 1 .......................... 2 So from 1 and 2 we get, E 1 = k l 1 .................................. 3 When switch s is connected to terminal 2 of the circuit: E 2 = V A J ' .......................... 4 Using the principle of the potentiometer: V A J α l 2 then V A J = k l 2 .......................... 5 So, from 4 and 5 we get, E 2 = k l 2 .......................... 6 So dividing 3 by 5 : E 1 E 2 = l 1 l 2 From the above equation we can compare the e.m.f. of the two cells if we know the length l 1 and l 2 .