Building series-parallel resistor circuits 2008-04-18 05:34:40 Once again, when building battery/resistor circuits, the student or hobbyist is faced with several different modes of construction. Perhaps the most popular is the solderless breadboard: a platform for constructing temporary circuits by plugging components and wires into a grid of interconnected points. A breadboard appears to be nothing but a plastic frame with hundreds of small holes in it. Underneath each hole, though, is a spring clip which connects to other spring clips beneath other holes. The connection pattern between holes is simple and uniform: Suppose we wanted to construct the following series
-parallel combination circuit on a breadboard: The recommended way to do so on a breadboard would be to arrange the resistors in approximately the same pattern as seen in the Read more:Building
Re-drawing complex schematics 2008-04-18 05:33:20 Typically, complex circuits are not arranged in nice, neat, clean schematic diagrams for us to follow. They are often drawn in such a way that makes it difficult to follow which components are in series and which are in parallel with each other. The purpose of this section is to show you a method useful for re-drawing
circuit schematics in a neat and orderly fashion. Like the stage-reduction strategy for solving series-parallel combination circuits, it is a method easier demonstrated than described. Let's start with the following (convoluted) circuit diagram. Perhaps this diagram was originally drawn this way by a technician or engineer. Perhaps it was sketched as someone traced the wires and connections of a real circuit. In any case, here it is in all its ugliness: With electric
What is a series-parallel circuit? 2008-04-18 05:30:59 With simple series
circuits, all components are connected end-to-end to form only one path for electrons to flow through the circuit: With simple parallel circuits, all components are connected between the same two sets of electrically common points, creating multiple paths for electrons to flow from one end of the battery to the other: With each of these two basic circuit configurations, we have specific sets of rules describing voltage, current, and resistance relationships. Series Circuits:Voltage drops add to equal total voltage.All components share the same (equal) current.Resistances add to equal total resistance. Parallel Circuits:All components share the same (equal) voltage.Branch currents add to equal total current.Resistances diminish to equal total resista
Kirchhoff's Current Law (KCL) 2008-04-18 05:30:03 Let's take a closer look at that last parallel example circuit: Solving for all values of voltage and current in this circuit: At this point, we know the value of each branch current and of the total current in the circuit. We know that the total current in a parallel circuit must equal the sum of the branch currents, but there's more going on in this circuit than just that. Taking a look at the currents at each wire junction point (node) in the circuit, we should be able to see something else: At each node on the negative "rail" (wire 8-7-6-5) we have current splitting off the main flow to each successive branch resistor. At each node on the positive "rail" (wire 1-2-3-4) we have current merging together to form the main flow from each successive branch resistor. T Read more:Current
Kirchhoff's Voltage Law (KVL) 2008-04-18 05:28:13 Let's take another look at our example series circuit, this time numbering the points in the circuit for voltage reference: If we were to connect a voltmeter between points 2 and 1, red test lead to point 2 and black test lead to point 1, the meter would register +45 volts. Typically the "+" sign is not shown, but rather implied, for positive readings in digital meter displays. However, for this lesson the polarity of the voltage reading is very important and so I will show positive numbers explicitly: When a voltage is specified with a double subscript (the characters "2-1" in the notation "E2-1"), it means the voltage at the first point (2) as measured in reference to the second point (1). A voltage specified as "Ecg" would mean the voltage as indicated by a digital mete Read more:Voltage
Volume I - DC 2008-04-12 04:27:22 Ø Chapter 1: BASIC CONCEPTS OF ELECTRICITY · Static electricity · Conductors, insulators, and electron flow · Electric circuits · Voltage and current · Resistance · Voltage and current in a practical circuit · Conventional versus electron flow Read more:Volume
Building simple resistor circuits 2008-04-12 04:04:04 In the course of learning about electricity, you will want to construct your own circuits using resistors and batteries. Some options are available in this matter of circuit assembly, some easier than others. In this section, I will explore a couple of fabrication techniques that will not only help you build the circuits shown in this chapter, but also more advanced circuits. If all we wish to construct is a simple single-battery, single-resistor circuit, we may easily use alligator clip jumper wires like this: Jumper wires with "alligator" style spring clips at each end provide a safe and convenient method of electrically joining components together. If we wanted to build a simple series circuit with one battery and three resistors, the same "point-to-point" construction techn Read more:Building
Correct use of Ohm's Law 2008-04-12 04:02:51 One of the most common mistakes made by beginning electronics students in their application of Ohm's Laws is mixing the contexts of voltage, current, and resistance. In other words, a student might mistakenly use a value for I through one resistor and the value for E across a set of interconnected resistors, thinking that they'll arrive at the resistance of that one resistor. Not so! Remember this important rule: The variables used in Ohm's Law equations must be common to the same two points in the circuit under consideration. I cannot overemphasize this rule. This is especially important in series-parallel combination circuits where nearby components may have different values for both voltage drop and current. When using Ohm's Law to calculate a variable pertaining to a single compo Read more:Correct
Power calculations 2008-04-12 04:02:31 When calculating the power dissipation of resistive components, use any one of the three power equations to derive the answer from values of voltage, current, and/or resistance pertaining to each component: This is easily managed by adding another row to our familiar table of voltages, currents, and resistances: Power for any particular table column can be found by the appropriate Ohm's Law equation (appropriate based on what figures are present for E, I, and R in that column). An interesting rule for total power versus individual power is that it is additive for any configuration of circuit: series, parallel, series/parallel, or otherwise. Power is a measure of rate of work, and since power dissipated must equal the total power applied by the source(s) (as per the
Conductance 2008-04-12 04:02:07 When students first see the parallel resistance equation, the natural question to ask is, "Where did that thing come from?" It is truly an odd piece of arithmetic, and its origin deserves a good explanation. Resistance, by definition, is the measure of friction a component presents to the flow of electrons through it. Resistance is symbolized by the capital letter "R" and is measured in the unit of "ohm." However, we can also think of this electrical property in terms of its inverse: how easy it is for electrons to flow through a component, rather than how difficult. If resistance is the word we use to symbolize the measure of how difficult it is for electrons to flow, then a good word to express how easy it is for electrons to flow would be conductance. Mathematically, co
Simple parallel circuits 2008-04-12 04:01:23 Let's start with a parallel circuit consisting of three resistors and a single battery: The first principle to understand about parallel circuits is that the voltage is equal across all components in the circuit. This is because there are only two sets of electrically common points in a parallel circuit, and voltage measured between sets of common points must always be the same at any given time. Therefore, in the above circuit, the voltage across R1 is equal to the voltage across R2 which is equal to the voltage across R3 which is equal to the voltage across the battery. This equality of voltages can be represented in another table for our starting values: Just as in the case of series circuits, the same caveat for Ohm's Law applies: values for voltage, current, and re Read more:Simple
Simple series circuits 2008-04-12 04:00:57 Let's start with a series
circuit consisting of three resistors and a single battery: The first principle to understand about series circuits is that the amount of current is the same through any component in the circuit. This is because there is only one path for electrons to flow in a series circuit, and because free electrons flow through conductors like marbles in a tube, the rate of flow (marble speed) at any point in the circuit (tube) at any specific point in time must be equal. From the way that the 9 volt battery is arranged, we can tell that the electrons in this circuit will flow in a counter-clockwise direction, from point 4 to 3 to 2 to 1 and back to 4. However, we have one source of voltage and three resistances. How do we use Ohm's Law here? An important ca Read more:Simple
Hand calculator use 2008-04-12 03:59:11 To enter numbers in scientific notation into a hand calculator, there is usually a button marked "E" or "EE" used to enter the correct power of ten. For example, to enter the mass of a proton in grams (1.67 x 10-24 grams) into a hand calculator, I would enter the following keystrokes: [1] [.] [6] [7] [EE] [2] [4] [+/-] The [+/-] keystroke changes the sign of the power (24) into a -24. Some calculators allow the use of the subtraction key [-] to do this, but I prefer the "change sign" [+/-] key because it's more consistent with the use of that key in other contexts. If I wanted to enter a negative number in scientific notation into a hand calculator, I would have to be careful how I used the [+/-] key, lest I change the sign of the power and not the si
Metric prefix conversions 2008-04-12 03:58:46 To express a quantity in a different metric prefix that what it was originally given, all we need to do is skip the decimal point to the right or to the left as needed. Notice that the metric prefix "number line" in the previous section was laid out from larger to smaller, left to right. This layout was purposely chosen to make it easier to remember which direction you need to skip the decimal point for any given conversion. Example problem: express 0.000023 amps in terms of microamps. 0.000023 amps (has no prefix, just plain unit of amps) From UNITS to micro on the number line is 6 places (powers of ten) to the right, so we need to skip the decimal point 6 places to the right: 0.000023 amps = 23. , or 23 microamps (µA) Example problem: express 304,212 volts i Read more:Metric
Metric notation 2008-04-12 03:58:22 The metric system, besides being a collection of measurement units for all sorts of physical quantities, is structured around the concept of scientific notation. The primary difference is that the powers-of-ten are represented with alphabetical prefixes instead of by literal powers-of-ten. The following number line shows some of the more common prefixes and their respective powers-of-ten: Looking at this scale, we can see that 2.5 Gigabytes would mean 2.5 x 109 bytes, or 2.5 billion bytes. Likewise, 3.21 picoamps would mean 3.21 x 10-12 amps, or 3.21 1/trillionths of an amp. Other metric prefixes exist to symbolize powers of ten for extremely small and extremely large multipliers. On the extremely small end of the spectrum, femto (f) = 10-15, atto (a) = Read more:Metric
Arithmetic with scientific notation 2008-04-12 03:57:57 The benefits of scientific notation do not end with ease of writing and expression of accuracy. Such notation also lends itself well to mathematical problems of multiplication and division. Let's say we wanted to know how many electrons would flow past a point in a circuit carrying 1 amp of electric current in 25 seconds. If we know the number of electrons per second in the circuit (which we do), then all we need to do is multiply that quantity by the number of seconds (25) to arrive at an answer of total electrons: (6,250,000,000,000,000,000 electrons per second) x (25 seconds) = 156,250,000,000,000,000,000 electrons passing by in 25 seconds Using scientific notation, we can write the problem like this: (6.25 x 1018 electrons per second) x (25 seconds) If we take
Scientific notation 2008-04-12 03:57:27 In many disciplines of science and engineering, very large and very small numerical quantities must be managed. Some of these quantities are mind-boggling in their size, either extremely small or extremely large. Take for example the mass of a proton, one of the constituent particles of an atom's nucleus: Proton mass = 0.00000000000000000000000167 grams Or, consider the number of electrons passing by a point in a circuit every second with a steady electric current of 1 amp: 1 amp = 6,250,000,000,000,000,000 electrons per second A lot of zeros, isn't it? Obviously, it can get quite confusing to have to handle so many zero digits in numbers such as this, even with the help of calculators and computers. Take note of those two numbers and of the relative sparsity of n Read more:Scientific
Electric shock data 2008-04-12 03:51:02 The table of electric currents and their various bodily effects was obtained from online (Internet) sources: the safety page of Massachusetts Institute of Technology (website: [*]), and a safety handbook published by Cooper Bussmann, Inc (website: [*]). In the Bussmann handbook, the table is appropriately entitled Deleterious Effects of Electric
Shock, and credited to a Mr. Charles F. Dalziel. Further research revealed Dalziel to be both a scientific pioneer and an authority on the effects of electricity on the human body. The table found in the Bussmann handbook differs slightly from the one available from MIT: for the DC threshold of perception (men), the MIT table gives 5.2 mA while the Bussmann table gives a slightly greater figure of 6.2 mA. Also, for the "unable to let go" 60 Hz
Creating custom calibration resistances 2008-05-10 04:49:06 Often in the course of designing and building electrical meter circuits, it is necessary to have precise resistances to obtain the desired range(s). More often than not, the resistance values required cannot be found in any manufactured resistor unit and therefore must be built by you. One solution to this dilemma is to make your own resistor out of a length of special high-resistance wire. Usually, a small "bobbin" is used as a form for the resulting wire coil, and the coil is wound in such a way as to eliminate any electromagnetic effects: the desired wire length is folded in half, and the looped wire wound around the bobbin so that current through the wire winds clockwise around the bobbin for half the wire's length, then counter-clockwise for the other half. This is known as a Read more:Creating
, custom
Wattmeter design 2008-05-10 04:48:25 Power in an electric circuit is the product (multiplication) of voltage and current, so any meter design
ed to measure power must account for both of these variables. A special meter movement designed especially for power measurement is called the dynamometer movement, and is similar to a D'Arsonval or Weston movement in that a lightweight coil of wire is attached to the pointer mechanism. However, unlike the D'Arsonval or Weston movement, another (stationary) coil is used instead of a permanent magnet to provide the magnetic field for the moving coil to react against. The moving coil is generally energized by the voltage in the circuit, while the stationary coil is generally energized by the current in the circuit. A dynamometer movement connected in a circuit looks something like th
Bridge circuits 2008-05-10 04:47:49 No text on electrical metering could be called complete without a section on bridge circuits. These ingenious circuits make use of a null-balance meter to compare two voltages, just like the laboratory balance scale compares two weights and indicates when they're equal. Unlike the "potentiometer" circuit used to simply measure an unknown voltage, bridge circuits can be used to measure all kinds of electrical values, not the least of which being resistance. The standard bridge circuit, often called a Wheatstone bridge, looks something like this: When the voltage between point 1 and the negative side of the battery is equal to the voltage between point 2 and the negative side of the battery, the null detector will indicate zero and the bridge is said to be "balanced." The bridge'
Kelvin (4-wire) resistance measurement 2008-05-10 04:47:09 Suppose we wished to measure the resistance of some component located a significant distance away from our ohmmeter. Such a scenario would be problematic, because an ohmmeter measures all resistance in the circuit loop, which includes the resistance of the wires (Rwire) connecting the ohmmeter to the component being measured (Rsubject): Usually, wire resistance is very small (only a few ohms per hundreds of feet, depending primarily on the gauge (size) of the wire), but if the connecting wires are very long, and/or the component to be measured has a very low resistance anyway, the measurement error introduced by wire resistance will be substantial. An ingenious method of measuring the subject resistance in a situation like this involves the use of both an ammeter and a voltmeter. Read more:Kelvin
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