http://www.ck12.org Chapter 17. Circuits
An electric current, as mentioned above, is subject to resistance. If the voltage remains constant and the resistance
increases by a certain factor, the electric current decreases by the same factor. The currentIis, therefore, inversely
proportional to the resistanceR
I∝^1 R
Ohm, however, concluded that
I∝V
Combining the two proportions, we have
I∝VR
If the resistance is defined with unitsVA, it can be shown that the proportionality constant is one. Therefore,
I=VR
Ohm’s law can then be stated asR=VI
In honor of Georg Simon Ohm the unit of resistance is called the ohm. The ohm is represented using the Greek
symbol capital omegaΩ.
1 Ω=^11 VA=^1 ( 1 VC∗s)
If a potential difference of one volt produces an electric current of one ampere, then a resistance of one ohm is
present in the circuit.
Check Your Understanding
Find the current in an electrical circuit with a voltage source of 12Vand a resistance of 30Ω.
Answer:V=IR→I=VR=^1230 VΩ= 0. 40 A