Plastic film capacitors are more expensive, smaller, and have high insulation resistance. Energy stored by the capacitor when the voltage is increasing is released to the load when the voltage is decreasing. This helps to smooth out the flow of energy. Electrolytic capacitors are also used in photographic flash units. Capacitors are commonly used in conventional ignition systems to reduce arcing.
Variable capacitors consist of two interleaved sets of metal plates, one set fixed and one movable.
The air surrounding the plates serves as the dielectric. Such capacitors are used in radio tuners. This coincides with what is known as the conventional current, which is a current that is assumed to flow from positive to negative. A flashlight is an example of a series circuit and is one of the most simple DC circuits. In order to represent such a circuit, a pictorial diagram, which involves drawings that are similar to the physical appearance of the components, may be used.