[MUSIC] Now let's talk about simple circuits. A simple circuit is a circuit that has one source, one load, and the conductor that connects them. And this conductor displays a property of electrical resistance. So let's talk about electrical resistance. If electric current flows through a conductor, the free charge carriers, free electrons, move between the atoms of the atomic framework. In the process, collision frequently occur, deflecting the free electrons, and rerouting their motion. The conductor thus, exerts a resistance on the electric current that must be overcome by the voltage. Let's take a look at the illustration that demonstrates how the electrons move through the conductor. A conductor with a low resistance is better at conducting electric current, whereas a conductor with higher resistance is not so good at conducting current. The unit of electrical resistance is named after the German physicist, Georg Simon Ohm. The following statement hold true. The electrical resistance denoted by letter R, has the unit, ohm, which has the symbol Greek letter, Omega. The reciprocal of resistance is the so-called, conductance. Electrical conductance denoted by letter G, has the unit, Siemens, or S. Thus, the following is true. G equals 1, divided by R. The resistance of a conductor is also temperature dependent. Let's discuss components of an electric circuit. A simple electric circuit consists of the following components, as I mentioned before. The voltage source, such as a battery, or power supply. Consumer of load, such as an incandescent lamp. And connections between the voltage source and the load, such as cables and leads. A switch to open and close the circuit may be present, or may be omitted. If the load is connected to the voltage source, via leads, the circuit is closed, and current flows from the voltage source through the load. In electrical engineering, circuits are usually depicted in technical drawings known as circuit diagrams, whereby the individual components are represented by standardized circuit symbols. Here, additional pointer. Arrows have been included to show the directions of the source voltage, and the current being conducted. Let's talk about measuring voltage. Electrical voltage is measured with a voltmeter. The graphics illustrates the circuit symbol of a voltmeter, it's a circle with a letter V inside it. And you can also look at the pictures of the analog voltmeter, as found in a motor vehicle, where it is used to display the battery voltage. A conventional multimeter which may be used to measure voltage and other properties, and is normally provided with a variety of measurement ranges. To perform the measurement, the voltmeter has to be connected to the voltage to be measured. A voltage can only exist between two points, such as between the terminals of the voltage source, or load. To measure this, the voltmeter is connected in parallel to the component across which the voltage is to be determined.