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An electrical circuit in which each device (or resistor, for simplicity) connects directly back to the battery, rather than forcing the current to flow through the other resistors, as in a series circuit. Notably different from a series circuit because if light bulbs (always the classic example) are hooked up in parallel, then a) each bulb suffers no loss in brightness as more bulbs are added, and b) if a bulb burn out, the remaining bulbs stay lit, whereas in a series circuit, bulbs take brightness hits as more are added, and the entire circuit will go out if one bulb burns out (as any aggravated Christmas tree lights buyer can tell you). Unfortunately, these benefits come at the cost of increased energy usage; three bulbs hooked up in parallel will use three times as much current as three bulbs in series.

The equivalent resistance of resistors in parallel is their product divided by their sum; you must calculate two resistors at a time, though. So the equivalent resistance of a 20-ohm toaster, a 30-ohm refrigerator, and a 10-ohm lamp would be 5.45 ohms. As we can see numerically, a parallel circuit loses resistance as more devices are added--the exact opposite of a series circuit.

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