Advertisements
Advertisements
Question
Illustrate-combination of cells e.g., three cells, in parallel, explaining the combination briefly. Obtain an expression for current ‘i’ in the combination.
Advertisements
Solution
Combination of cells in parallel: Let there be n cells, each of e.m.f. E and internal resistance r, be connected in parallel as shown in the diagram.
Total e.m.f. across the point A and B is E
Total internal resistance
`1/"r"_1 = 1/"r" + 1/"r" + 1/"r".... = "n"/"r"` (if there are n cells)
or r1 = `"r"/"n"`
But total resistance of circuit = R + `"r"/"n" = ("nR" + "r")/"n"`
∴ Current i = `"Total e.m.f"/"Total resistance"`
`= "E"/("R" + "r"/"n")`
`= "nE"/("nR + "r"")`
It is advantageous to join cells in parallel when the internal resistance of each cell is quite high as compared to the external resistance R.
Then, Approximately, i = `"nE"/"r"` (neglecting R).
RELATED QUESTIONS
The substance having infinitely high electrical resistance is called:
(a) conductor
(b) resistor
(c) superconductor
(d) insulator
In series combination of resistances ______.
A graph is plotted taking p.d. along y-axis and electric current along x-axis. Name the physical quantity that represents the slope of this graph (Fig.).
Why are thick copper wires used as connecting wires?
Write an expression for the resistance of a conducting wire in terms of its length and area of cross-section.
Two resistors of 4Ω and 6Ω are connected in parallel to a cell to draw 0.5 A current from the cell. Calculate the current in each resistor.
Calculate the quantity of heat that will be produced in a coil of resistance 75 Ω if a current of 2A is passed through it for 2 minutes.
Show how you would connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of 4 Ω.
