Educator

Electric Current

• Electric current (I) is a continuous flow of charge. It is defined as how much charge (q) passes by in an amount of time:
  

  I = q t .

  It uses the unit of amperes (usually shortened to amps) (A). One amp is one coulomb per second.
• The amount of current that will flow between two points is connected to the electric potential difference between those two points. A large voltage means more current flow.
• Some materials resist current flow more than others. We account for this with resistance (R).
  

  R = V I .

  Resistance is measured in ohms (Ω).
• If we know a material's resistivity (ρ), we can find its resistance depending on its length (L) and cross-sectional area (A):
  

  R = ρL A .

• Since energy is involved in moving charge around, and we have a continuous flow of charge, electric current is connected to power (energy per unit of time). There are many ways to express this relationship:
  

  P = IV ,        P = I2R ,       P = V2 R .

• If we want a sustained current, we need a sustained voltage source. The two main ways to create a long-term voltage source are through generators and batteries.
• While electricity flows very quickly, each individual charge actually flows quite slowly. This is because all the charges start flowing at once as soon as the switch is flipped, like turning on a hose full of water.