5 identical cells of internal resistances 1.5 Ω each are connected in parallel combination. Find the equivalent internal resistance of the cells.

CONCEPT:

• Grouping of Cells: In a series grouping of cell’s their emf’s are additive or subtractive while their internal resistances are always additive.
• If dissimilar plates of cells are connected together then their emf’s are added to each other while if their similar plates are connected together then their emf’s are subtractive

Series grouping: 

• In series grouping anode of one cell is connected to the cathode of other cells and so on.

• If n identical cells are connected in series

1. Equivalent emf of the combination Eeq = nE
2. Equivalent internal resistance req = nr

Parallel grouping:

• In parallel grouping, all anodes are connected at one point and all cathode are connected together at other points.

• If n identical cells are connected in parallel

1. Equivalent emf of the combination Eeq = E
2. Equivalent internal resistance req = r/n

CALCULATION:

Given - number of cell = 5 and internal resistances (r) = 1.5 Ω

• The equivalent internal resistance of the cells is 

⇒ req = r/n

⇒ req = 1.5/5 = 0.3 Ω