Introduction to Basic Electronics Lecture -2
Basic Electronics What is electricity? Voltage, Current, Resistance DC/AC Ohm s Law Capacitors & Inductors Conductor & Insulator
What is Electricity? Everything is made of atoms There are 118 elements, an atom is a single part of an element Atom consists of electrons, protons, and neutrons
Electrons (- charge) are attracted to protons (+ charge), this holds the atom together Some materials have strong attraction and refuse to loss electrons, these are called insulators (air, glass, rubber, most plastics) Some materials have weak attractions and allow electrons to be lost, these are called conductors (copper, silver, gold, aluminum) Electrons can be made to move from one atom to another, this is called a current of electricity.
Surplus of electrons is called a negative charge (-). A shortage of electrons is called a positive charge (+). A battery provides a surplus of electrons by chemical reaction. By connecting a conductor from the positive terminal to negative terminal electrons will flow.
Electricity Electricity is the flow of electrons so it is necessary to measure the charge. The basic unit for measuring charge is the coulomb or the letter C. 1 coulomb is equal to the charge of 6,250,000,000,000,000,000 electrons!!! 1C = 6.25 x 10 18 electrons
Voltage A battery positive terminal (+) and a negative terminal (-). The difference in charge between each terminal is the potential energy the battery can provide. This is labeled in units of volts. Water Analogy
Voltage Sources:
Voltage is like differential pressure, always measure between two points. Measure voltage between two points or across a component in a circuit. When measuring DC voltage make sure polarity of meter is correct, positive (+) red, negative (-) black.
Ground
Current Electric current is the amount of electrons, or charge, moving past a point every second. It is basically the speed of electron flow. The faster the electron flow, the higher the current. Current is represented by the letter I. The basic unit for measuring current is ampere(a). 1 A = 1 coulomb/sec = 6.25 x 10 18 electrons /sec
Current Uniform flow of electrons thru a circuit is called current. WILL USE CONVENTIONAL FLOW NOTATION ON ALL SCHEMATICS
To measure current, must break circuit and install meter in line. Measurement is imperfect because of voltage drop created by meter.
Current Direct Current(DC) The battery we have been using for a current/voltage source generates direct current, which simply means the current flows in only one direction.
Current Alternating Current(AC) The electrical current in your house is alternating current. This comes from power plants that are operated by the electric company. Those big wires you see stretching across the countryside are carrying AC current from the power plants to the loads, which are in our homes and businesses. The direction of current is switching back and forth 60 times each second.
Resistance When an electron is knocked out of an atom, it will fly off and hit another atom. If the electron strikes the atom with enough force, it will knock off another electron. The atom that was just knocked off will hit another atom and so forth. Note that every time an electron strikes another, it is transferring its energy. Some of the energy is converted into heat every time it is transferred. The voltage will drop as the energy is transferred over long distances. Thus a long wire has a higher resistance than a short wire.
Resistance All materials have a resistance that is dependent on crosssectional area, material type and temperature. A resistor dissipates power in the form of heat
Various resistors types
When measuring resistance, remove component from the circuit.
Resistor Color Code
Ohm s Law
Prototyping Board Example of how components are Inserted in the protoboard
Conductor Copper is considered to be a conductor because it conducts the electron current or flow of electrons fairly easily. Most metals are considered to be good conductors of electrical current. Copper is just one of the more popular materials that is used for conductors. Other materials that are sometimes used as conductors are silver, gold, and aluminum. Copper is still the most popular material used for wires because it is a very good conductor of electrical current and it is fairly inexpensive when compared to gold and silver. Aluminum and most other metals do not conduct electricity quite as good as copper.
Insulator Insulators are materials that have just the opposite effect on the flow of electrons. They do not let electrons flow very easily from one atom to another. Insulators are materials whose atoms have tightly bound electrons. These electrons are not free to roam around and be shared by neighboring atoms. Some common insulator materials are glass, plastic, rubber, air, and wood. Insulators are used to protect us from the dangerous effects of electricity flowing through conductors. Sometimes the voltage in an electrical circuit can be quite high and dangerous. If the voltage is high enough, electric current can be made to flow through even materials that are generally not considered to be good conductors.
Insulator Our bodies will conduct electricity and you may have experienced this when you received an electrical shock. Generally, electricity flowing through the body is not pleasant and can cause injuries. The function of our heart can be disrupted by a strong electrical shock and the current can cause burns. Therefore, we need to shield our bodies from the conductors that carry electricity. The rubbery coating on wires is an insulating material that shields us from the conductor inside. Look at any lamp cord and you will see the insulator. If you see the conductor, it is probably time to replace the cord.
Capacitance A capacitor is used to store charge for a short amount of time Battery Capacitor Unit = Farad Pico Farad - pf = 10-12 F Micro Farad - uf = 10-6 F
Capacitor Charging
Capacitor Discharge
Inductance