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.