Suppose you have a simple circuit that contains only a 9-Volt battery and a resistor of $120 \Omega$. What is the current in the wire?

• $\Delta V = 9\text{ V}$
• $R = 120 \Omega$

• Current

• The wire has no (negligible) resistance.
• The circuit is in a steady state.
• Approximating the battery as a mechanical battery.
• There is no outside influence on the circuit.

• We represent Ohm's Law as $\Delta V = IR$.
• We represent the situation with following picture.

We have assumed that the battery and the wire contribute negligible resistance to the circuit. So the resistance of the circuit is simply the resistance of the resistor: $R = 120\Omega$.