Ohms Law and Resistors 
Written by Bryce Ringwood  
This program provides a means of determining the Voltage, Current or Resistance in a series circuit. It also calculates the power dissipated in the resistor. UsesUsed to calculate dropper resistor values and just about everything in an electrical circuit. Use to calculate power in a load.
Data Entry SectionEnter the unknown quantity as zero. Press "Calculate" Button to get the third quantity. In this program, SI suffixes can be used on input, and are used on output. For example, you can enter 1k for 1000 Ohms  and so on. Additional ResultsExample  Mains DropperA "Pye Piper" radio contains 5 Valves UY41, UL41, UBC41, UF42 and UCH42. The sum of the heater voltages is 121 Volts, and a mains dropper resistor is needed to drop the supply from 230 Volts. The filament current is 0.1 Amp. The voltage drop is clearly 230  121 volts = 109 Volts. From Ohms law, we calculate the resistance (unknown) = 1090 Ohms. The power dissipated = 10.9 Watts. Practically, you may have to settle for a 1000 Ohm resistor rated at 20 Watts. TheoryOhm's law is a basic property of materials.
The law was named after the German physicist Georg Ohm who, in 1827, described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire.
Formulae
\displaystyle{ V = IR}
\displaystyle{ I = {V\over R}}
\displaystyle{ R = {V\over I}}
\displaystyle{ P = IV} Where: $V$ = Applied Voltage $I$ = Current $P$ = Power $R$ = Resistance By the way, you will see the terms "amperage" and "wattage" (and hear them too). The correct expressions are "current" and "power". For a program in 'C' for Ohm's law, see experimenters corner. ReferencesHorowitz P, Hill W "The Art of Electronics"  Cambridge University Press, 1988 pp 3334
