Presentation on theme: "Prof. Thomas G. Re Introduction to electricity Nassau Community College."— Presentation transcript:
Prof. Thomas G. Re Introduction to electricity Nassau Community College
Everything is made up of Atoms Atoms can makeup Liquids Solids Gas Each Atom Contains a A nucleolus containing both Neutrons (No Charge) Protons (Positive charge) Electrons (negative charge)
Each atom struggles to keep the same number of protons as electrons. Combining one or more atoms create a molecule. Molecules are the basic Building blocks of real objects H 2 O (A molecule of Water has two hydrogen and one Oxygen atom) CO 2 (A molecule of Carbon Dioxide has one Carbon Atom and two Oxygen Atoms) Water of course is a liquid and Carbon Dioxide is a gas.
Some Molecules will give up electrons quicker than others. These molecules make good conductors since electrons will move from atom to atom easier within the material. Good conductors include Silver Gold Platinum Copper Aluminum
Good Conductors will give up electrons easily. Insulators hold onto their electrons and become poor conductors. Insulators include Glass Plastic Electricity therefore, is the flow of electrons through conductors in a circuit.
With Electricity, electrons will flow from a negative charge to a positive charge. That is, Electrons or the flow of electricity will go from the negative terminal on a battery to the positive. The Conventional flow of electricity though, travels from the positive charge to the negative. Use of the Conventional flow of electricity is used to help trace the flow of electricity through a circuit.
The Volt was named after Alsandro Volta He developed the first battery The electronic pressure in a circuit is named after him (voltage is the measurement of this pressure). The symbol used for voltage is E Voltage is the electrical force or pressure that push the electrons flowing through a circuit. Think of voltage as the pressure that is placed on a towns water supply from a water tower. This pressure helps deliver water to each of the houses connected to the water supply.
Current is the amount of electrons flowing through a circuit. Measured in Amps. The electronic symbol I is used for current. If the water tower is the pressure or voltage of a circuit, think of the flow of water to each of the homes as the current.
Restricts or controls the flow of electricity (current) in a circuit. With the water example, think of resistance in a circuit like kinking a garden hose. The more kinks that you put in the hose, the flow of water is reduced. Using that analogy it becomes clear that the diameter of a wire will also create resistance in a circuit. In addition to this, the length of a wire will also add to the resistance of a circuit.
Resistance is used in a circuit to control the flow of electricity for electronic circuits. For Example when you use Light Emitting Diodes(LEDS) Most LEDs require a maximum current of 20 mA (milli Amps) (and forward voltage of 2.5V (will discuss later) If you use a 9 volt battery to power the LED, you will need Resistors in the circuit to reduce the current and protect the LED. Too much current to the LED will damage the LED.
Resistors can be added to the circuit to reduce the current. Too little resistance will damage the LED. Too much Resistance will not allow the LED to light. Just the right balance of resistance will allow the LED to light safely. Laws and properties have been discovered in electricity and electronics that make it easier to determine this balance.
Discovered and developed by Georg Ohm E=IR E is the voltage I is the Current R is the resistance If the resistance of the circuit is fixed, as the voltage to the circuit is increased, so does the current. If voltage is fixed and the resistance is increased then the current is decreased.
Ohms Law is one of many formulas that can be used to determine the correct voltage, resistance and current for a circuit to operate safely. Other variations of the Law include I=E/R R=E/I For Example: if a bulb requires.03 Amps and the circuit has the resistance of 200 ohms E=.03*200 = 6V That is 6V will be required to safely run this circuit.
Symbols are used to indicate components that are used in a circuit. The illustration to the right show a couple of symbols that are used for common components. Using these symbols in drawings called schematics help in planning your electronic circuit. We will only be dealing with DC circuits for now.
There are two basic types of circuits that will be discussed here. Series circuit where all components follow a straight unidirectional path from the positive terminal of your power source to the negative. Parallel circuits where components of the circuit can be drawn in parallel to each other With parallel circuits the path of electricity goes through multiple branches in the circuit. Most circuits discussed here will be using both series and parallel circuits and different laws are used for each.
To the left you will see the two examples of a series and parallel circuit. Of course you can have circuit designs that will use both parallel and series circuits. Being able to identify the different types of circuits dictates the laws that are needed in each.
Total resistance of a series circuit is equal to the sum of each components resistance. That is R t = R 1 + R 2 + ….. + R n Current in a series circuit is constant (that is it is the same at each component. I t = I 1 = I 2 = …..= I n Kirchhoff's Voltage law states that the total voltage drops across each component is equal to the voltage that is applied. That is E t = E 1 + E 2 + …… + E n (Simplified)
Of course the previous example was simplified. Because voltage drops are negative, if you add the drops together, you will have a negative number. The applied voltage to the circuit is positive. If you ad the total voltage drops to the total applied voltage, you should get zero. This will help us figure out the resistance in a circuit in the lab that follows.