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OHM'S LAW
There are 2 formulas which will help you to understand the relationship between current, voltage, resistance and power. 

 
OHM'S LAW
BASE FORMULAS  P=I*E  E=I*R   
TO FIND VOLTAGE  E=P/I  E=I*R  E=SQR(P*R) 
TO FIND CURRENT  I=P/E  I=E/R  I=SQR(P/R) 
TO FIND POWER  P=I*E  P=E 2 /R  P=I 2 *R 
TO FIND RESISTANCE  R=E 2 /P  R=E/I  R=P/I 2 
  • P-POWER IN WATTS 
  • E-ELECTROMOTIVE FORCE IN VOLTS 
  • I-ELECTRICAL CURRENT IN AMPS 
  • R-ELECTRICAL RESISTANCE IN OHMS 
    • EXAMPLE: 
    If you want to know how much power dissipation there is in a 10 ohm resistor if 12 volts is applied to the resistor terminals, use the formula P=E^2/R. 12volts squared is 144. P=144/10. Power=14.4 watts. If you wanted to know how much current was flowing through the resistor, you would use the formula I=E/R. Current through the resistor is 1.2 amps. 


    If you want to try a few for yourself, you can check your math below for a couple of the formulas. 

Find: Power dissipation and Current flow from Resistance and applied Voltage 
Enter: 
Resistor Value? = Ohms 
Applied Voltage? = Volts 
to find power dissipation and current flow through resistor. This program is useful to determine the minimum resistor power rating. 
Power Dissipation = Watts 
Current Flow = Amps 

Find: Resistance from applied Voltage and Current flow 
Enter: 
Applied Voltage? = Volts 
Desired Current Flow? = Amps 
to find the resistor value needed to limit the current to the above value when the above voltage is applied. This is a useful program to find the proper resistor for a light emitting diode if you know how much current you want to flow through the LED. 
Resistor Value = Ohms 

Find: Voltage and Current from Power and Resistance 
Enter: 
Power Dissipation? = Watts 
Resistor Value? = Ohms 
to find the current flow through the above resistor and the voltage which is required to produce the power entered above. It will also tell you how much voltage is applied to, and current flowing through the speakers attached to an amplifier at a given power output. 
Applied Voltage = Volts 
Current Flow = Amps 

You should remember: 
1.If you have any 2 of the 4 electrical properties, you can find the other properties through Ohm's law. 

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