Circuit basics: Replacement resistance

We have already learned about resistance in circuits. A nice feature of resistance is that you can avoid having many resistors for LEDs in parallel. This can be done by replacing them by one resistor with another resistance. This resistance can be caculated like:

1/Rreplacement = 1/R1 + 1/R2 + 1/RN.

For example, replace 2x680 Ohm resistors:

1/680 + 1/680 = 0.0029
1/0.009 = 340 Ohm.

Or replace 3 resistors:

1/680 + 1/680 + 1/680 = 0.004
1/0.004 = 226 Ohm.

The following circuit proves this: