# Current and Ohm's Law

• The term electromotive force is an antique expression for the modern term voltage.
• Current is the bulk motion of electric charges. The units of current are amperes = Coulombs per second.
• Current is always defined to flow from high (positive) to low (negative) voltage. When a current is carried by electrons, the electrons move opposite to the direction of the current.
• Continuing the analogy between the electric potential and the gravitational potential: just as water flows from high elevations to low elevations, so current flows from high voltages to low voltages.
• In some materials, the amount of current depends linearly on the voltage across a material; such materials obey Ohm's Law:
```             I
-----  = const     or      V = IR
V
```
where R is the resistance of the material.
• However, many materials do NOT obey Ohm's Law -- it is not universal.

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