Unknown Current
Suppose we have a voltage across a circuit of 10Vdc and a total resistance of 127k and current is unknown then you would do the following:
10Vdc/127k ohms = 10/127,000= 78.7 µ amps.
This means if you had a voltage across the resistor of 10v and 127k ohms of total resistance then the total current flowing through the circuit is 78.8 µ amps or 0.000078 amps.
Unknown Voltage
Now lets suppose that we have a circuit with a total resistance of 5k ohms and a known current amount of 42 mili amps. The formula for finding voltage would be as follows:
42m amps *5k ohms = 0.042/5000=210volts
Unknown resistance
In this final example we have a voltage source of 15vdc and a current flow of 34µ amps, the following formula would be:
15vdc/34µ amps =15/0.000034 = 441176.470 ohms or 441k ohms.
