Electric Cell

The electric cell is a device which converts chemical energy into electrical energy.

SIMPLE CELL

Emf of cell (E): The energy given by the cell in the flow of unit charge in the whole circuit (including the cell) is called it’s electromotive force (emf). Its unit is volt.

Potential difference (V) : The energy given by the cell in the flow of unit charge in a specific part of electrical circuit (external part) is called potential difference. Its unit is also volt.

Internal resistance (r): The electrolyte through which a current flows has a finite resistance which is called the internal resistance.

Equation of cell E =V + ir (Here E > V)

Grouping of cells

Series grouping:  if n identical cells are connected in series

(a) Equivalent emf of the combination E_eq =nE

(b) Equivalent internal resistance r_eq=nr

(c) Main current = Current from each cell = i = nE/(R+nr)

Parallel grouping: If n identical cells are connected in parallel

(a) Equivalent emf of the combination E_eq =E

(b) Equivalent internal resistance r_eq=r/n

(c) Main current = Current from each cell = i = nE/(nR+r)

Mixed Grouping: If n identical cells are connected in a row and such m rows are connected in parallel

(a) Equivalent emf of the combination E_eq =nE

(b) Equivalent internal resistance r_eq=nr/m

(c) Main current = Current from each cell = i = nE/(mR+nr)