Ohm's law describes how voltage, current, and resistance in a circuit are related. Ohm's law can be written in three equivalent forms; the formula you use depends on the quantity you need to determine. _____________________________________________________________________________ 1. Ohm's Law can be stated as follows:
I= V/R
For a constant resistance – If the voltage applied to a circuit board increased, the current will increase; and if the voltage is decreased, the current will decrease.
For constant voltage – if the resistance in a circuit is increased, the current will decrease; If the resistance is decreased, the current will increase. ______________________________________________________________________________
2. Ohm's law can also be stated another equivalent way:
V=I*R
With this formula, you can calculate voltage in Volts if the current in amperes and resistance in ohms are known _______________________________________________________________________________
3.There is a third equivalent way to state Ohm's law:
R=V/I
This form of Ohm's law is used to determine resistance in ohms if the values of voltage in volts and current in amperes are known. ________________________________________________________________________________
Example
My track voltage is 13Volts and the bulb I am about to use is a 1.5V 15mA device. I need to find the voltage limiting resistance value.
13V – 1.5V = 11.5V (the bulb voltage was subtracted from the track voltage) 15mA = 0.015A Using the R=V/I Ohm's law form we got following:
R=11.5/0.015 R= 767 Ohms Choose closest resistor value R=780 Ohms.