
PARALLEL ELECTRIC CIRCUITS have elements arranged side by side (in parallel) along the circuit. The current therefore flows through each element at the same time. If one element is removed then the circuit is not broken because current can still flow through the collateral route. This animation shows a simple DC electrical circuit with one bulb. About halfway through the movie a second bulb appears in parallel. Notice how both bulbs remain as bright as the original lone bulb and how the amount of current flowing increases.
EXPLANATION: as the second bulb appears, so the resistance of the circuit drops. In this simple case we ignore the resistance of the wire. Adding an identical second bulb in parallel will give the electric current two routes around the circuit instead of one. The resistance therefore drops by half (there is twice the available pathway for the current). The voltage provided by the battery (cell) stays the same. With half the resistance, the current doubles. With double the current flowing down the same voltage drop, the energy dissipated by the entire circuit doubles. This doubled energy is now divided between the two bulbs. Each bulb therefore has half of double the energy or the same as before. Consequently, when you add a second bulb in parallel, the brightness of the bulbs is the same as the brightness of the bulb in the original circuit.
SI UNITS used in electricity: