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.