“If your meter doesn't do autoranging, each position on the dial will have a number beside it. This number means “no higher than.” For instance if you want to check a 6-volt battery, and one position on the voltage section of the dial is numbered 2 and the next position is numbered 20, position 2 means “no higher than 2 volts.” You have to go to the next position, which means “no higher than 20 volts.” (Make Electronics by Platt, p. 5)
Resistance
Resistance is an opposition to current and is caused by a lack of available charge carriers or a difficulty in moving charge carriers through a material. The unit of resistance is the ohm, which is name in honor of Georg Simon Ohm (1787-1854), a Bavarian-born German physicist. The Greek capital letter omega (O) is often used as an abbreviation for the work ohm. In mathematical equations, the ohm is represented by the capital letter R (Electricity and Electronics by Newman, p. 62)
“Resistors are used in a wide variety of applications in all types of electronic circuits. Their main function in any circuit is to limit the amount of current or to produce a desired drop in voltage. Resistors are manufactured in a variety of shapes and sizes and have ohmic values ranging from a fraction of an ohm to several megohms. The power or wattage rating of a resistor is determined mainly by its physical size. There is, however, no direct correlation between the physical size of a resistor and its resistance value.” (Grob's Electronics, 11th by Schultz, p. 54)
How do you select a resistor, O when using a breadboard (current, I), battery (volts, V) and LED
“When choosing a resistor for a circuit, first determine the required resistance value as R = V/I. Next, calculate the amount of power dissipated by the resistor using any one of the power formulas. Then, select a wattage rating for the resistor that will provide a reasonable amount of cushion between the actual power dissipation and the power rating of the resistor. Ideally, the power dissipation in a resistor should never be more than 50% of its power rating, which is a safety factor of 2. A safety factor of 2 allows the resistor to operate at a cooler temperature and thus last longer without breaking down from excessive heat. In practice, however, as long as the safety factor is reasonably close to 2, the resistor will not overheat.” (Grob's Basic Electronics, 11th by Schultz, p. 92)
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“Power is dissipated in resistance as heat. Resistors that must radiate a lot of heat must be larger than those that only radiate a small amount of heat. To accommodate the need for various power requirements, color coded resistors are manufactured in a variety of sizes. Some resistors are wound with nichrome wire and can radiate far more heat than their smaller color coded cousins. There wire-wound resistors are often too hot to touch.” (Electricity and Electronics by Newman, p. 104)
Transistor
“A three-terminal semiconductor device that can amplify an ac signal or be used as an electronic switch” (Grob's Basic Electronics, 11th Edition by Mitchel E. Schultz, p. 1167)
Ohm's Law and Power
“Volts, ohms, amps, and power are generally the major units of concern in any circuit. The interrelationships among voltage, current, and resistance are expressed by Ohm's law, but often an Ohm's law unit must be found in terms of power.” (Electricity and Electronics by Newman, p. 102)
Voltage = Current x Resistance
Volts = Amps x Ohms
V = IR
The basic law of electricity in this chart form will help you to determine whether you can safely add more load to an existing circuit or whether it's time to add another circuit. Ever wonder how much power flows through your TV, airconditioner or radial-arm saw? Or what the total power load might be if every appliance and light were turned on in your home at the same time?
You can find out by using the Ohm's Law chart above. In it, I stands for amps (Intensity), E for volts (Electromotive force), R for ohms (Resistance) and W for watts (Power). Thus it's easy to compute any of these four valves by Ohm's Law if you know at least two of them. For example: you buy a new toaster rated at 1100 watts. You want to find out how much current it uses. Use the amperes section of the chart and pick out the formula that uses the two elements you know-wattage (1100) and voltage (115). Substituting in the formula I = W/E you get I = 1100/15 or I = 9.5 amps. To find power, use the watts section of the chart and pick the two elements you know, W = E*I.
Every electrical device has a clue to its rated power on it. It is given in watts, amperes or horsepower (1hp = 746 watts). Use the appropriate formula and you can figure the electrical load at any point in your service.
In your home circuit, the voltage remains constant, usually 115 volts. Amperage draw will vary with the number of lights and appliances connected into each circuit. Stoves, hot-water heaters and air conditioners are usually on a separate, 220-volt circuit.
To figure the current load a standard circuit can safely carry, determine its wattage capacity by multiplying the voltage (115 volts) by the size of the fuse (usually 15 amps). Total the wattage of each item already in the circuit and subtract this from the wattage capacity. The remainder will tell you how much you can add safely. (Popular Mechanics Do-It-Yourself Encyclopedia, Vol 1, p. 109)
Light-Emitting Diodes (LEDs)
Flat side of a LED is negative side, flat like ”-“
“Each electrical circuit will contain these basic electrical quantities: voltage, amperage, and resistance. Each of these quantities must be controlled to permit the electrical circuit to operate properly.” (Electricity 10th Edition by Gerrich, Dugger, DeLucca, p. 15)
Pressure/Voltage
Pressure/Voltage/Volts/V/Electromotive Force
Pressure/Voltage - nature always trying to maintain an electrical balance, force or pressure is equal to the difference between the negative charge and positive charge. Units of volts. Volts also known as Electrical Pressure, Difference of Potential, Electromotive Force, and Voltage.
Current/Intensity I/Amps A
“Since current is the movement of charge, the unit for stating the amount of current is defined in rate of flow of charge. When the charge moves at the rate of 6.25 X 10^{18} electrons flowing past a given point per second, the value of the current is one ampere (A). This is the same as one coulomb of charge per second. The ampere unit of current is named after Andre M. Ampere (1775-1836). The symbol for current is I or i for intensity, since the current is a measure of how intense or concentrated the electron flow is. Two amperes of current in a copper wire is a higher intensity than one ampere; a greater concentration of moving electrons results because of more electrons in motion. Sometimes current is called amperage. However, the current in electrons circuits is usually in smaller units, milliamperes and microamperes.” (Grob's Basic Electronics, 11th Edition by Mitchel E. Schultz, p. 36)
Current - flow of electrons through a conductor from the negative to positive poles, units of electric current is ampere/amps, number of electrons that pass a given point in a given time. Symbol I
Conventional Current vs Actual Electron Flow - Electrical Engineers use Conventional Current in all formulas, that is the current is the movement of the holes/gaps from a positive terminal to a negative terminal. Actual Electron flow is the opposite, instead of the holes/gaps, concerned with the electron that is moves from a negative terminal to a positive terminal.
Resistance - nature of the material/metal in which the electrons flow. Iron offers more resistance than Copper. Output of resistance is heat and light. Units of Ohm. Brass, Porcelain and Rubber are good insulators (high resistance or no flow of electrons)
“The resistance to the flow of current is measured in ohms (O). One ohm of resistance will allow one ampere to pass when one volt pressure is applied.” (Electricity 10th Edition by Gerrich, Dugger, DeLucca, p. 17)
Checking Continuity with the Ohmmeter - A wire conductor taht is continuous without a break has practically zero ohms,Ω of resistance. Therefore, the ohmmeter can be useful in testing for continuity. This test should be done on the lowest ohm range. There are many applications. A wire conductor can have an internal break which is not visible because of the insulated cover, or the wire can have a bad connection at the terminal. Checking for zero ohms between any two points along the conductor tests continuity. A break in the conducting path is evident from a reading of infinite resistance, showing an open circuit. (Grob's Basic Electronics, 11th Ed, by Mitchel E. Schultz, p. 247-8)
How AC Generators and Motors Work
The United States Army present T.F.9 3107 Motors and Generators - Part II AC Motors and Generators
Series and Parallel Circuits
Series circuit the electricity flows in a single loop, so if you have a series of lights connected, if you unconnect one, they all go out.
Parallel circuit the electricity has multiple paths/loops to travel in, so if you unconnect one light, the remaining lights will still be on.
Capacitors
farad (F), millifarad (mF), microfarad (µF)
a capacitor stores energy in the form of an electrostatic field between its plates (Capacitor - Wikipedia)