Circuits Unlike lightening, in low voltages electrons do not discharge through air, inspected a medium called circuit is required to link between concentrated and depleted regions. Depending to medium resistance, electrons move in a different quantity to the other end. In previous chapter we learned about attraction between positive and negative charges, as well on the possibility of making bridges between them. By letting only a certain number of electrons through a circuit, we can limit the current. Such a current can make a load heats up or glow a filament in a lamp. Limiting the flow of current is possible because of resistance property found in materials. It looks like a tollgate in a free, slows down the traffic. Along the way of passing, some electrons collide with each other, causing a reduction or changing their direction. In overall, it causes a partial lose of energy in the form heat. In another analogy, we may think of current as a flow of water in a pipe and voltage as pressure of water. As the diameter of pipe reduces, the amount of water reduces as well because of more resistance. Current is a flow of charges. By closing the poles of an electrical source via a medium, we make a circuit. Such a source could be a battery. By adding a switch and an electrical bulb, we will have a controlled circuit to light up the bulb.  Circuit Experiment A above mentioned circuit was one of the earliest experiments done by Tomas Edison which gave way to more supplicated experiments in a later time. Doing the above experiment, you will need following items.   Electricity we use at homes and offices come from power plants that produce in large amount and transfer it via overhead power line to the points of consumption. The unit used for current is Ampere (Amp) which is 6.25×1018 electrons passed per second in a circuit. Instead of memorizing such a large number, we use another unit called coulomb after the name of discover of current. The potential difference between the sides is called voltage. The unit of voltage is volt which is the name another scientist who built the first battery. As we discussed before, energy is defined as the ability to do work. Volt is the amount of electrical charge required to make one coulomb to do one specific amount of work, namely one joule. In analyzing the circuits, three named units are very important. Any extra current or voltage may break down a circuit. On the other too small to them may not activate the circuit properly. In the same way, too big a resistance does not let enough electricity flow in the circuit. Contrary, too small resistance may cause a big devastating current in the circuit.    Parallel and series circuits In a single loop, electrons flow in only one predicted path. Such a circuit is called “Series circuit” Whenever there are other paths for current flow, we will have parallel circuit. In a parallel circuit the voltage between two ends is equal, but the amount of current flow in each branch may differ largely. Insuch a means, we may draw more current from the source, without making a breakdown in total circuit.  Electric Motors Simplest form of a motor uses of a multi wire inside a magnet, connected to a battery. Whenever current passes through the coil, the produced electromagnetic field force turns the coil, trying to put the coil in the direction of north-south of magnet poles. By changing rapidly the direction of current, we may have a turning coil.