obviously can be extended to a series combination of any number n of resistors R , R ....., R n . The equivalent resistance R eq is R eq = R + R + . . .
+ R n ( . ) Consider now the parallel combination of two resistors (Fig. . ).
The charge that flows in at A from the left flows out partly through R and partly through R . The currents I , I , I shown in the figure are the rates of flow of charge at the points indicated. Hence, I = I + I ( . ) The potential difference between A and B is given by the Ohm’s law applied to R V = I R ( .
) Also, Ohm’s law applied to R gives V = I R ( . ) ∴ I = I + I = ( . ) If the combination was replaced by an equivalent resistance R eq , we would have, by Ohm’s law eq I ( . ) Hence, eq ( .
) We can easily see how this extends to three resistors in parallel (Fig. . ). FIGURE .
Parallel combination of three resistors R , R and R .