# ATAT 105 Basic Electricity > # [[T105 Week 2| ◀️ ]] &nbsp;[[T105 Home| Home ]] &nbsp;[[T105 Week 4| ▶️ ]] &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; [[QR T105 Week 3| 🌐 ]] ># [[T105 Week 3|Week 3]] >- [[T105 Week 3#Electrical Circuits|Electrical Circuits]] >- [[T105 Week 3#Circuit Components|Circuit Components]] >- [[T105 Week 3#Resistor Colour Codes|Resistor Colour Codes]] ># [[T105 Week 3#Lab|Lab]] >- [[T105 Week 3#Ohmmeter|Ohmmeter]] >- [[T105 Week 3#2 Resistors|Resistors]] >- [[T105 Week 3#3 Resistors in a Circuit|Resistors in a Circuit]] >- [[T105 Week 3#4 Voltage and Resistors|Voltage and Resistors]] >- [[T105 Week 3#5 Variable Resistance|Variable Resistance]] >[!jbplus|c-blue]- Lesson Intro >### What >In this lesson you will learn more about basic circuits and measuring electrical values in a circuit. > >### Why > >A basic understanding of electricity is important for any aviation technician as electrical circuits are everywhere in aircraft, and all technicians, even if they do not actually repair electrical equipment, must be able to operate professionally and safely where electricity is concerned. You will use this knowledge throughout your aviation career. >### Approach and Objectives > >By understanding the following topics, you will have achieved the learning outcome for this lesson. Consult your course outline for the learning outcomes and other details of this course. > >#### Course Learning Objectives > >- CLO 10. Assemble a functional electrical circuit using components according to a given circuit diagram. >- CLO 11. Show using a Digital Multimeter (DMM) the measurement of voltage, current and resistance in a circuit. > >### Testing > >You will be tested on this material on Assignment 2, the Midterm, and the Final Test, as per the [[T105 Intro#Testing and Grades|testing strategy]]. >[!jbplus|c-blue]- Prof >### Objectives > >This week we keep increasing the pace and difficulty. Resistors, how to measure them, their effect on voltage, and an intro to a bunch of other components. > > ### Theory >For the theory course, a review to get us situated, a brief runthrough of various components, and resistors: color codes, and how to measure. With luck, you will have time to start the lab worksheet before the end of class. Even if you didn't bring the sheets to class, they have access to a pdf from the SSG and they can quickly transcribe once in the lab. >### Lab >For the lab, PPE is required, and you should refuse admittance to students who are not correctly equipped. Measuring resistance is new, so the fundamentals must be stressed: Power off, measure in parallel, isolate the component (where applicable). Since they have to also measure voltage, changing the meter settings and the power can lead to issues. Close supervision, a good opening brief, and lots of repetition will likely help here. You should insist on them doing the calculations for tolerance every time it comes up. Not hard, good practice. ## Electrical Circuits ### Required Elements Remember what we have learned about a [[T105 Week 1#A Basic Circuit|basic circuit]]. Here are those requirements rephrased: - A source of electrical energy - A load device to use the electrical energy produced by the source - Conductors to connect the source to the load  ### Open Circuit We also learned about [[T105 Week 1#Open Circuit|open circuits]]. For a circuit to be complete, there must be at least one continuous path from one of the source terminals, through the load and back to the other terminal. If there is any interruption or break in the path, the circuit is said to open, and there is no flow of electrons. ![[Pasted image 20210808115953.png|350]] ### Short Circuit We also touched on [[T105 Week 1#Short Circuit|short circuits]]. If there is a path from one source terminal to the other without passing through the load the circuit is shorted. Not only is there no work being done, but the absence of resistance in the circuit allows excessive current to flow. In this case, unless a [[fuse]] or circuit breaker opens the circuit, the wiring and the source can be damaged. ![[Pasted image 20210808120041.png|350]] ![[Pasted image 20210808120049.png|350]] Note that a short may cause a shortcut through only a part of the circuit. It is still referred to as a short circuit, but it may only cause one part of the circuit to be denied current, and may not remove all of the resistance in the circuit causing battery or component damage. Of course, this kind of short circuit is still undesirable because the circuit will be unserviceable, that is, it will not perform its intended function.  You have experimented in the lab with a basic circuit. We added things, we changed some things around, and we changed voltages. We also measured voltages and tried to observe what was happening. We will continue to dig deeper and wider, and start working with more and more complex circuitry. Don't worry though, we will take this a step at a time. Let's look at some other things that you will find and work with in electrical circuits. ## Circuit Components We will now enjoy a brief introduction to different circuit components so that we can begin experimenting and measuring in the lab. You need to understand the basic concepts of these components as you will be going into more detail in following courses in the program. This is of course especially true for avionics students, but maintenance students also will be learning more in this area. ### Conductors %%==[[Master QB1#Q01001|Q]]==%% The purpose of a conductor is to provide a path for electrons to flow from a source, through the load, and back to the source with minimum resistance. While for most of our work we will consider wires to have no resistance at all, in reality wires have very small resistance, but not zero. [[V What is a Conductor|🎞]] #### Resistance in Wires The resistance of a conductor is affected by three things: - its physical characteristics - its dimensions - its temperature ##### Physical characteristics %%==[[Master QB1#Q01002|Q]]==%% Resistivity is the resistance of a standard length and cross-sectional area of a conductor. Copper wire is generally used as it has 2/3 the resistance of equivalent aluminum wire. Remember though that aluminum has the advantage of being lighter than copper, so it still has applications in aviation where weight is always a consideration. Other factors such as load carrying ability, durability, and flexibility must also be considered. Therefore, the choice of a conductor is often a compromise.  ##### Dimensions %%==[[Master QB1#Q00909|Q]] [[Master QB1#Q00923|Q]] [[Master QB1#Q01003|Q]]==%% The amount of resistance varies directly with the conductor's length. That is, as length increases for a given conductor, its resistance increases. $ R \quad \alpha \quad l$ Where $R$ is the resistance and $l$ is the length of the conductor. The symbol $\alpha$ indicates that the items on either side of it are proportional. So, raise one side, the other side is also raised in proportion, and also in reverse then, lower one side, the other side is also lowered. So a wire that is twice as long will have double the resistance. Because the resistance of wire is low, it takes a fair bit of wire before this resistance becomes an issue. At all lengths though, the losses to resistance must be accounted for in the design of the circuit. The resistance of a conductor varies inversely with its cross-sectional area. In other words, as a conductor's cross-sectional area increases, resistance decreases. This is a simple formula, and you learn about how to make sense of these in your [[T110T SSGW05#Formula Relationships|math course]]. For now, just see this as the opposite of the previous one, that is, if you increase the area, you decrease the resistance. $ R \quad \alpha \quad \frac{1}{A}$ Where $R$ is the resistance and $A$ is the cross sectional area of the conductor, and $\alpha$ indicates a proportional relationship between the two. So here we see that the thinner a wire, the more resistance it offers. There are fewer electrons to push around, and therefore less current is possible. This appears as resistance. ![[Pasted image 20210808120752.png|350]] %% #JB Q00923 isn't in the eCentennial question library. manually add it when the AWG section is written. AWG has been added below.%% ##### Temperature %%==[[Master QB1#Q01004|Q]]==%% Metals have what is known as a positive temperature coefficient of resistance. This means that the resistance of the material increases as its temperature increases. For practical purposes both copper and aluminum exhibit small changes in resistance with the temperatures encountered in flight. You will learn how to interpret graphs like this in the [[T110T SSGW12#Basic Graphs and Interpretation|math course]] as well. ![[Pasted image 20210808120853.png|350]] ![[Pasted image 20210808120900.png|350]] #### Wire Gauge >[!aside]- Ref [🌎](https://www.techtarget.com/searchnetworking/definition/American-Wire-Gauge) American Wire Gauge (AWG) is the standard way to denote wire size in North America. In AWG, the larger the number, the smaller the wire diameter and thickness. The largest standard size is 0000 AWG, and 40 AWG is the smallest standard size. AWG is for single-strand, solid, round, electrically conductive wire. It was first introduced in 1857 as a standard to replace the various measurements used by different manufacturers. AWG size does not include the size of the insulation protecting a wire. A smaller gauge (larger size) wire can safely conduct more electricity than a larger gauge (smaller size) wire. Decreasing the AWG size of a wire by three will double the cross-sectional area of a wire and double the amount of current it can carry. Changing the AWG size by 10 will change the cross-section by tenfold. Since aluminum is not as good of a conductor as copper, for calculating how much current an aluminum wire can carry compared to a copper one, consider it as being 2-gauge AWG larger. AWG primarily describes single-strand solid wire. When multiple conductors, or stranded wire, use AWG, it gives the equivalent single-strand cross-section in AWG of all the strands cross-sections added together. Stranded wire typically has three numbers to define it. These numbers include the AWG equivalent size, the number of strands and the AWG size of each strand. We have seen that the larger the cross-section of a wire, the less its resistance. Also, the larger the cross-section, the greater the amount of current ([amperage](https://whatis.techtarget.com/definition/ampere)) the wire can safely carry before overheating. A wire with a smaller gauge (larger diameter) can carry more power than one with a larger gauge. In general, a lower AWG number is better in terms of heat toleration than higher AWG. AWG is of primary importance for wires that will carry electrical power -- for example, home or business electrical wiring, extension cords or high-power wire in automotive or audio use. If too small a wire is used (high AWG), then the wire may overheat, melt or catch fire. Therefore, it is important that the current carrying capacity of a wire or circuit be considered. Larger wire uses more metal and is, therefore, more expensive. More metal also equals more weight, and therefore in aviation, it is important to have only the size of wire necessary to do the job safely. #### Ground Path Most aircraft electrical systems are of the single wire type, meaning the aircraft structure provides the ground path through which the current flows. We will discuss this more a little later, but for now, just think of the ground as the completion of a circuit. In other words, to satisfy the requirement to have a complete path for current to flow, the aircraft structure, being metal and therefore a conductor, provides it.  ### Switches %%==[[Master QB1#Q00918|Q]]==%% We have experimented with a basic circuit in the lab. We saw the effects of current flow, and then we looked at an open circuit, and deduced that current wasn't flowing, as evidenced by the light bulb not illuminating. We asked you in a worksheet question what you would do if you had to turn the light on and off frequently. If you guessed that we would install a switch, you were correct. Most practical electrical circuits utilize some sort of switch to safely control the flow of electrons. These are mechanical devices that connect a conductor with the circuit. When opened, the conductor path is interrupted. There are many types of switches, and several different methods of mechanically altering the circuit this way. There are also electronic switches, having no mechanical moving parts, but later for that. The switch that you will see in the lab may be the simplest example of a switch you will ever see. You might guess that this type of switch is not in common use because it is not easy to use, the user is exposed to the conductor in the switch, and the contact made, while solid, is not very consistent. Try playing with it in the lab and see if you think it's a high quality switch, like those you're used to seeing everywhere else. The advantage of this switch however, is that is is very easy to see it in operation. Note also that the schematic symbol for the switch is printed right on it.  %% #JB what caption make %% The two most common switches used on aircraft are the enclosed toggle switch and rocker switch. These switches are actuated by either moving the baseball bat-shaped toggle or by pressing on one side of a rocker.  You might ask why the different types? Why would we just not use the same kind of switch? It's because some other functionality has been included. Rocker switches often have lights to display switch status, and can be activated with the touch of a finger. Toggle switches often have detents that prevent accidental actioning of the switch. There are other reasons, many of which will be obvious once you see how they are used specifically. ### Relays %%==[[Master QB1#Q01005|Q]] [[Master QB1#Q01006|Q]]==%% It is often necessary to control a circuit carrying a large amount of current from a remote location. An example is the starter circuit for an aircraft engine. A starter motor requires a great deal of current and, therefore, a large conductor is required. A relay is used to prevent having to run a large conductor to the instrument panel where the switch is located and then back down to the starter. So in simple terms, a relay is simply a remotely controlled electrical switch. With a relay, a small amount of current energizes an electromagnet which, in turn, closes a set of contacts to complete a second circuit. The operating principles of relays will be more fully explained during the lesson on electro-magnetism.   ### Protective Devices %%==[[Master QB1#Q01007|Q]]==%% Protective devices are installed in electrical circuits to prevent damage caused by overloading a circuit or a short in a circuit. This way, if a circuit goes into a high current situation for whatever reason, the protective device will open the circuit, with results that you now know: current will no longer flow. #### Fuses %%==[[Master QB1#Q01008|Q]] [[Master QB1#Q01009|Q]]==%% A [[fuse]] is made of a low-melting-point alloy enclosed in a glass tube. The fuse is installed in a circuit and, when current flow becomes excessive the metal alloy melts and opens the circuit. This way, if a circuit goes into a high current situation for whatever reason, the fuse will be destroyed, opening the circuit before any other parts of the circuit can be destroyed. We say the fuse is destroyed, because there is no way to rebuild the melted metal, and so it will never work again.   Some fuses are designed to withstand a momentary surge of current, but create an open if the current is sustained. These slow-blow fuses have a small spring attached to a link so when the sustained current softens the link, the spring pulls the link apart and opens the circuit. It is important that you replace fuses with the correct rating and type. If you put a slow-blow fuse in a circuit that requires a normal fuse, you risk the same damage as if the circuit was not protected. The opposite scenario would be to install a fast-blow fuse in a circuit with high fluctuations, and the circuit will be constantly blowing fuses instead of riding out the peaks. #### Circuit Breakers %%==[[Master QB1#Q00916|Q]] [[Master QB1#Q01010|Q]]==%% It is inconvenient to replace a fuse in flight, so most aircraft circuits are protected by circuit breakers. Like fuses, circuit breakers protect the wiring and components of a circuit by automatically opening the circuit if current flow becomes excessive. Once the circuit cools, the breaker is easily reset by moving the operating control. You may see these referred to as CB's. It is important to keep in mind, and you will learn more about this later, that if a circuit breaker (or fuse) is activated, there was a reason. Some malfunction or short happened in the circuit to cause overcurrent. You must determine this reason before replacing a fuse or resetting a circuit breaker. If not, you reintroduce the situation that was causing overcurrent, and increase the possibility of damage or heat or fire.   So, circuit protection devices protect circuits from overload and shorts. Recap: Overloading a circuit results from connecting loads that are too large for the wiring. This results in too much current flowing through wires that cannot handle it. You will learn a lot more about electrical loads later. A short, as we have discussed, occurs when part of a circuit in which full system voltage is present comes in direct contact with the return side of the circuit. When a short occurs, a path for current flow with little or no resistance is established. This results in large amounts of current flow and conductor heating very quickly. ### Resistors Resistors can take many forms and be made of different materials. They all have the same function however: >Limit (resist) the flow of current    #### Types and Construction ##### Carbon Type %%==[[Master QB1#Q01011|Q]]==%% Resistor construction is most commonly the carbon type, formally known as Carbon Composition. Powdered carbon with precise amounts of impurities is suspended in a glue-like binder, allowing for high precision of resistance values, and with adjustments to the amounts of carbon and binder, many different values are easily produced. Adding more carbon to the mixture lowers the resistance. Can you figure out why? Carbon type resistors are encased in a protective housing, and have leads protruding from both ends for connection to the circuit. They have coloured rings that indicate the nominal resistance value, and the tolerance. The word nominal refers to the value as stated by the manufacturer. This value is rarely exactly as labelled, but the tolerance tells us the range within which a particular resistor will fall and still be called serviceable, that is, the correct value. We will dive into this before the end of the lesson today.  ##### Variable Resistors %%==[[Master QB1#Q01012|Q]]==%% When it is necessary to be able to change the amount of resistance in a circuit, variable resistors are used. Variable resistors are either carbon composition or wire wound type, and may have different mechanisms or techniques for varying the resistance. Here, like switches, we now have technology to do this without mechanical moving parts as well.  ##### Rheostats %%==[[Master QB1#Q01013|Q]] [[Master QB1#Q01014|Q]]==%% Rheostats are variable resistors that have only two terminals, one at one end of the resistance material and the other at a sliding contact. Most rheostats are wire wound and, therefore can dissipate a great deal of power. Rheostats vary the amount of current flow in circuits and are commonly used in aircraft to control cockpit lighting. Notice in the schematic symbol that there is no connection at the right side of the resistive material. By moving a mechanism, the arrow moves along the resistive material, offering more or less resistance depending on its position. Effectively, the position of this moveable wiper mechanism allows the current to bypass a portion of the resistive material within the rheostat.  ##### Potentiometers %%==[[Master QB1#Q01015|Q]] [[Master QB1#Q01016|Q]]==%% Potentiometers are variable resistors that have three terminals, one at each end of the resistance material and the other at a sliding contact. Potentiometers change the amount of voltage in a circuit, and are often used as voltage dividers. We will explore this in depth a little later. Notice the difference in the schematic symbol for the potentiometer and the rheostat. See that the potentiometer has three connections. %% #JB added the line below re: using a potentiometer like a rheostat pls verify%% However, it is also possible to use a potentiometer like a rheostat if you only make use of two of the connections.  ### Component Symbology All components used in electrical circuits are represented by symbols in drawings, blueprints, and illustrations in schematic form. You must become familiar with the components commonly used in basic circuits, together with their schematic symbols. This is made a little more difficult by the fact that there are many schematic symbols, and that there are variances between countries and different electrical authorities. We will try to show you as many of these as possible so that you get used to seeing them in schematics of various sources. A reminder that your training aid in the lab has a schematic symbol beside every component as well, including a simple straight line for a wire. [[Pasted image 20210808122444.png|➡]] ## Resistor Colour Codes %%==[[Master QB1#Q00917|Q]] [[Master QB1#Q00920|Q]] [[Master QB1#Q00921|Q]] [[Master QB1#Q01017|Q]] [[Master QB1#Q01018|Q]] [[Master QB1#Q01019|Q]]==%% As mentioned earlier, carbon type resistors have coloured bands around their protective coating. These coloured bands indicate the nominal value of the resistor, as well as the tolerance of the resistor. [[Pasted image 20210808122508.png|➡]] This system is like a secret code, and we will now learn the key to decode the secret message on all carbon type resistors. The colours represent a few different things, depending on their position. First, the colours in order: - Black - Brown - Red - Orange - Yellow - Green - Blue - Violet - Grey - White - Gold - Silver - (no band) First, we must memorize the order of the colours in order to use the colour code system by memory. There are several different mnemonics for this, some of them vulgar, and some just a little weird. You can pick from these examples or make up your own, just so long as you can remember the colours in order. The first letter of these words represents the first letter of the colours in order: >Bad Beer Rots Our Young Guts But Vodka Goes Well - Get Some Now >Black Bears Raid Our Yellow Green Bins Violently Grabbing Whatever Goodies Smell Nice If you use your fingers, and start with the first B as 0, you can find out immediately the number corresponding to the colour. Let's use an example to go through the bands successively. A little practice with this will speed up your reading of a resistors value significantly (And it's easier than multiplication tables).  A resistor colour coded YELLOW-VIOLET-RED is deciphered as: Yellow is 4, and Violet is 7, so our resistance value begins with 47. Refer to the [[Pasted image 20210808122508.png|Colour Code Chart]]. Observe that the third band is called the multiplier. One way to remember the value of the multiplier is to take it as describing the number of zeros. Red's value is 2 according to the chart, so, there are two zeroes in the multiplier, so we have 47 x 100 = 4700 For a final answer of 4700Ω. Note the Ω symbol. You may not be used to seeing it, and it is very close to looking like a 0. Keep this in mind when writing the symbol as well, try to be as clear as possible in your work. We continue to the next band to find out the tolerance, but we see that we were only given three bands. Therefore, in the tolerance column, we look up the value for "no band" and see that it is 20%. This means that the acceptable resistance value for this resistor is between 4700Ω plus 20% and 4700Ω minus 20%. Some quick calculations then: 20% of 4700 is 940 So the actual value of the resistor will be between 3760 (4700-940) and 5640 (4700+940) ohms. This is often and correctly referred to as 4.7KΩ. We use metric system prefixes to write resistor values more concisely. We'll get you completely briefed on this in the math course. If in our previous example we required a resistance that was closer to 4.7KΩ we would have to buy a resistor with a tighter tolerance. When working with resistors, remember their primary function, which is to provide resistance to current. This process generates heat, which if excessive could injure you or the circuit. If a circuit has very high current, it may require a beefier resistance, no matter what the resistive value is. To specify this, resistors also have a power rating. A resistor of the correct power rating will handle the current that it is asked to in a circuit that is functioning correctly. Why did we specify "functioning correctly"? Because if something happens in the circuit, such as a short, and a high current situation occurs, the resistor may be in jeopardy of being destroyed. But, since we know what we're doing, we put a fuse or a circuit breaker in the circuit, and our resistor will never see such abuse. ## Lab [[T105L WS03.pdf|Lab Worksheet]] | [[T105L EQ W03|Equipment List]] [[T105 Lab Week 3 Video Runthrough|🎞️ Video Runthrough]] Safety rules have not changed. Review them here: [[T105L SAFETY|Safety Briefing]] ## Lab Prep Remember what we learned when we were introduced to [[T105 Week 2#Resistance|measuring resistance]]. There are two key things that you must always take into account when measuring resistance: >Power must be removed from the circuit >measuring individual components must be done in isolation from the circuit. ##### Pre-lab You can complete the pre-lab portion of the worksheet by referring to the [[T105 Week 3#Resistor Colour Codes|Resistor Colour Code Chart]]. ##### In Lab You will measure each of the resistors on the worksheet to verify their serviceability. You may declare the resistor serviceable when: - The resistor has a measured resistance that is within its labelled tolerance limits. To accomplish this, you will need to become familiarized with the ohmmeter function of a digital multimeter. ### Ohmmeter To use the benchtop multimeter, you will need to both turn on power to the workbench and the multimeter itself:  If the main power switch is in the on position but not glowing, check that the circuit breaker to the left of it is not tripped and reset the circuit breaker as necessary or ask an instructor for assistance. Refer to the [[Bench DMM.pdf|User's Guide]] for full details. On page 35, you can see all the capabilities of this meter. To keep things simple, we will provide steps here to get you using the meter: Press the button labelled with Omega (Ω) to put the multimeter in Ohmmeter mode. (blue circle)  ![[Pasted image 20210922041043.png|200]] Verify on the display that the 2W mode is selected. If not, press the button again. ![[Pasted image 20210922040859.png|350]] Verify that the display indicates auto-range, ![[Pasted image 20210922041244.png|350]] and if not, press the blue Shift key and the up arrow. (green circle)  You will need to connect test leads or cables to the ohmmeter through which it will interact with your electrical circuit. Plug the ends of your cables to the colour-coded sockets marked in the photo and diagram below:  ![[Pasted image 20210922041410.png|350]] Notice that you will not need to refer to the manual again, because if you examine closely, you can identify the socket for Ω, and follow the black line to the socket for the black lead. The one to the left of it is labelled Ω 4W, which is a different use of the meter that we will not get into for this course. The right hand one is the default input, and as such, you see the V, Ω, and two symbols for capacitors and PN junctions. (later for those) Depending on what is on the free end of the cables, that is, banana plugs or test leads, that you just connected to the multimeter, you can now either probe or directly plug the ohmmeter into your circuit:   Note: Because the whole point of a multimeter is to be a versatile yet accurate measuring instrument, it has the capability to display its measured resistance at different ranges. Ranging is normally taken care of automatically by the multimeter, but you can manually set it to operate at various different resistance ranges by pressing the up and down arrow buttons depicted below:  %% #JB maybe reference T110 for SI units (kilo, milli etc) %% You can revert back to Auto Range by first pressing the blue Shift button, followed by pressing the up arrow button. ## 2. Resistors If you have not yet done so, fill in all of the blocks on the lab worksheet except the "measured" and "serviceable?" rows. A refresher on reading resistor colour codes can be found [[T105 Week 3#Resistor Colour Codes|here]] for your refence. To complete the table from the pre-lab section of the worksheet, measure each resistor using the ohmmeter.  ## 3. Resistors in a Circuit Refresh your memory about the use of the [[T105 Week 2#Power Supply|power supply]]. >REMINDER: When measuring resistance, power must be turned off ### a) Construct this circuit, and observe the brightness of the lamp:  [➡](<TA_305.png>) ### b) We will now move the placement of the light bulb and observe the effects:  [➡](<TA_305_2.png>) Answer the applicable worksheet question(s). ### c) Construct the following circuit and measure the resistance of R₁, R₂, and R₃. Answer the applicable worksheet question(s). > ! This is where you need to make sure there is no power applied to the circuit! Ensure the output of the power supply is not lit.  [➡](<TA_308.png>) ### d) Your readings in the previous exercise should not have matched your earlier measurements of these resistors. This is because your meter is measuring throughout the circuit, not just the resistor. To remedy this, we isolate the resistor from the circuit: ![[Pasted image 20210922044522.png|350]] Following this example, measure each resistor again and answer the questions in the worksheet. ## 4. Voltage and Resistors To further explore the behaviour of resistors in a circuit, we will now measure voltage and make some observations. Construct this circuit. A little reminder that you should try to construct this on your own, and click on the little blue arrow box only if you need help, or to verify your work.  [➡](<TA_308.png>) #### Measure voltage from a reference point. For each of these readings, fill in Row A on your lab worksheet. Notice how "voltage over R₃" etc. is notated in the column headers. Also, ensure your answers include a VDC after the measurement to indicate that these are Direct Current Volts. Place the black lead at the bottom of R₃ and the red lead at the top of R₃ and note the voltage reading. Note how we could have phrased that differently or more simply: measure the voltage at R₃. Now, *leaving the black lead at the bottom of R₃* move the red lead to the top of R₂ and measure the voltage. We could say: measure VR<sub>32. Now, measure VR₃₂₁. To be clear, we will measure across all three resistors here. Note how we now have different voltages available at different points in our circuit. We could connect a conductor and feed this exact voltage to whatever circuitry we choose. But what if these voltages are not quite what we desire? How could we change these voltages? In your circuit, swap resistors R₁ and R₂. Fill in Row B on your worksheet. Now see how the use of different resistances can be used to create different voltages in our circuit. ## 5. Variable Resistance As you are seeing, questions in the worksheet are designed to guide you to consider and observe closely the finer points of what we are doing in the lab. For the following exercise, it's more important that you play around a little with the circuit and your measurements. Keep playing until there are no surprises for you, that you begin to have an instinct about what to expect. If there is the slightest puzzlement, get a prof over and get chatting about it. Build this circuit.  You will probably want to use banana plugs to connect the voltmeter for this exercise. #### a) Measure the voltage over the lamp. Vary the potentiometer while observing the change to the voltage around the lamp and the change in brightness that results. #### b) Remove the potentiometer from the circuit and measure the resistance across it while adjusting it. See how we now can change the voltage in a circuit by means of a control, rather than having to change resistors. There are applications for both methods, i.e choosing and designing a fixed voltage, or designing the circuit to be variable. Place your leads here, and experiment measuring voltage and resistance while varying the potentiometer. ![[Pasted image 20210922053430.png|350]] See if you can relate what you are doing here with the circuit we saw earlier with R₁, R₂, and R₃. >Clean up your bench, return the training aids, and sweep bench surfaces and floors. > # [[T105 Week 2| ◀️ ]] &nbsp;[[T105 Home| Home ]] &nbsp;[[T105 Week 4| ▶️ ]] &nbsp; &nbsp; [[QR T105 Week 3|🌐 ]] &nbsp; &nbsp;[[FB T105|Please Help]]