CHAPTER THREE current and electric circuits. One foundational unit of electrical measurement is the unit of the coudl. Which is a measure of electric charge proportional to the number of electrons in an unbalanced state. One kunam of charge is equal to 6250 with 15 zeros behind it, electrons or 6.250 times 10. To the 18th power. The symbol for electric charge quantity is the capital letter Q.

The amp is equal to one coulomb of electrical one coulomb of electrons passing by a given point in a circuit in one second of time. Current is the rate of electric charge motion through a conductor The diagram one app is equal to the electrons passing by a in one second of time. Remember that there will never be a continuous or uniform flow of electrons within a wire unless they have a place to come from, and a place to go. In other words, they need a source and a destination. Now, with an electron source pushing new electrons into the wire on the left side, electrons flow out of the wire on the right side. This source can take many forms sources supply a constant push of charges called a electromotive force or EMF and it also provides a reservoir or a pool.

Charges otherwise there would be a buildup of charge in one end of the conductor. This setup provides a continuous loop or a path. For the flow of charges we call it a circuit. One such source is a battery whose constant emf is measured in volts. Any source of voltage including batteries have two points for electrical contact. In this case, we have point one and point two in the diagram.

The horizontal lines of varying length indicate that this is a battery, and they further indicate the direction in which the battery voltage will try to push electrons through a circuit. This is the electrical symbol for a battery. Notice the positive and negative signs to the immediate left of the battery symbol the name The end of the battery is always the end with the shortest dash and the positive and the battery is always the end with the longest dash. Since we have decided to call electrons negatively charged the negative end of the battery is that end which tries to push electrons out of it. Likewise, the positive end is the end which tries to attract electrons with the positive and negative ends of the battery not to connect it to any to anything, there will be a voltage between those two points, but there will be no flow of electrons to the battery, because there is no continuous path for the electrons to move.

The same principle holds true for the water reservoir and a pump analogy. Without a return pipe back to the pond. stored energy in the reservoir cannot be released in the form of water. water flow. Once the reservoir is completely filled up, no flow can occur No matter how much pressure the pump may generate, there needs to be a complete path or a circuit for the water to flow from the pond to the reservoir and back to the pond in order to have a continuous flow occur. We can provide such a path for a battery by connecting a piece of wire from one end of the battery to the other, forming a circuit with a loop of wire, we will initiate continuous flow of electrons in a clockwise direction in our diagram, so long as the battery continues to produce voltage, and the continuity of the electrical path isn't broken, electrons will continue to flow in the circuit.

Following the metaphor of the water moving through a pipe this continuous uniform flow of electrons through a circuit called a current, so long as the voltage source keeps pushing in the same direction the electrons, the electron flow will continue to move in the same direction. In the circuit. This single direction flow of electrons is called a direct current or DC. Notice the positive and negative signs drawn at the end of the break in the circuit and how they correspond to the positive and negative signs. Next to the battery terminals. These markers indicate direction that the voltage attempts to push the current that potential direction is commonly referred to as polarity.

Remember that voltage is always relative to two points. Because of this fact, the polarity of a voltage drop is relative between two points whether a point in a circuit gets labeled with a positive or a negative depends on the other point to which it is referenced. If we include a light bulb in the electric circuit, we find that a set amount of current flows after the switch is closed. We say that the light bulb resists the flow of current. different size light bulbs allow different amounts of current to flow. Depending on the amount of resistance the light bulb introduces into the circuit.

Because it takes energy to force electrons to flow against, the opposition of the resistance, there will be a voltage manifested or a voltage drop between any points in the circuit with resistance between them. It is important to know that the amount of current the quantity of electrons are charged moving past a given point every second In his uniform throughout the circuit. In electron flow notation, we follow the actual motion of electrons in the circuit, but the positive and negative labels seem to be backwards. Doesn't matter really, how we designate charge flow in a circuit. Not really so long as we're consistent in the use of our symbols, you may follow an imaginary direction of current, which is the conventional flow, or the actual electron flow with equal success insofar as circuit analysis is concerned. However, looking at the worldwide conventional flow notation, the flow of current is always considered from positive to negative.

Electronic electrons move from the negative side of the battery through the conductor. To the positive side, but this is considered as positive current flowing from positive to negative. The force motivating electron flow in a circuit is called electromotive force or EMF it is measured in volts and at times referred to as voltage. voltage is a specific measure of potential energy that is always relative between two points. When we speak of a certain amount of voltage being present in a circuit we are referring to the measurement of how much potential energy exists to move electrons from one particular point in that circuit to another particular point. without reference to two particular points the term voltage has no meaning voltage has a polarity And is usually indicated with a positive and negative sign.

The voltage is said to be rising from negative to positive, or we can sometimes describe it as a voltage drop, which is referred to from positive to negative. Current by standard acceptance flows from positive to and is sometimes indicated with an arrow and the symbol I. Any kind of resistance to current flow is sometimes indicated by a squiggly line, as seen here, or a block and labeled with the symbol R. As the current flows through the resistance runs through the resistor, it will set up a potential difference across the resistor as before the voltage difference or draw ROP is indicated by a positive and negative sign. And the voltage drop is associated with the resistor is sometimes labeled V with a subscript R. But the key to note here is that there is a potential difference a cross the resistor, due to current flowing through that resistor.

The symbol given for each quantity is the standard alphabetical letter used to represent that quantity in analogy in an algebraic equation. Standardized letters like these are common in in physics and engineering, and are internationally recognized. The unit abbreviation for each quantity represents the alphabetical symbol used as a shorthand notation for its particular unit of measure. Each unit of measurement is in this case has been named after an early experimenter, in electricity. For example, the amp is named after the Frenchman Andre m ampair. The volt is named after an Italian Alessandro Volta.

And the old is is named after a German George Simon olm. The abbreviation is ohms and it is r omega and it's the last letter of the Greek alphabet. The mathematical symbol for each quantity is meaningful as well. The R for resistance and the V for voltage are both self explanatory whereas AI for currency seems to be a bit weird. The eye is thought to have been happening. To be represented by intensity or electron flow, and the other symbol for voltage is sometimes E which stands for electromotive force.

All these symbols are expressed using capital letters except in the case where a quantity, especially current and voltage is described in terms of a brief period of time, sometimes called an instantaneous value, and there'll be more on this later. And this ends chapter three