Loven gælder for alle kredsløb, som opfylder [[Ohms lov]] .  Ohms Lov angiver at strøm er proportional med spændingen , hvilket igen vil sige at den givne komponent opfører sig som en [[Ohmsk modstand]]. Ohms lov udtrykker at for en given spænding ''U'' over et kredsløb med resistansen ''R'' vil strømmen være:
<ref>
{{cite book
 | title = Electrical Engineering: The Theory and Characteristics of Electrical Circuits and Machinery
 | edition = 2nd
 | author = Clarence V. Christie
 | publisher = McGraw-Hill 
 | year = 1917
 | page = 79
 | url = http://books.google.com/books?id=XMxIAAAAMAAJ&pg=PA79&dq=current+square+%22joule%27s+law%22+%22ohm%27s+law%22+resistance&lr=&as_brr=1&as_pt=ALLTYPES&ei=2papSfebD5ykkQTh4cSdBA
 }}</ref>
<ref>
{{cite book
 | title = McGraw-Hill's Engineering Companion
 | author = Ejup N. Ganic and Tyler G. Hicks
 | publisher = McGraw-Hill Professional
 | year = 2002
 | isbn = 9780071378369
 | page = 16.3–16.5
 | url = http://books.google.com/books?id=hld7ft72bzEC&pg=PT642&dq=applicable+%22joule%27s+law%22+%22ohm%27s+law%22&lr=&as_brr=3&as_pt=ALLTYPES&ei=RJqpScXBH5eKkAS_rsi8CA#PPT644,M1
 }}</ref>
Samfund Fysik