1 00:00:05,660 --> 00:00:08,400 >> In this video, we'll introduce some of 2 00:00:08,400 --> 00:00:11,445 the practical aspects of capacitors and inductors. 3 00:00:11,445 --> 00:00:13,020 As usual in the lab videos, 4 00:00:13,020 --> 00:00:15,390 I'll assume that you're getting the theoretical information about 5 00:00:15,390 --> 00:00:18,090 these devices from the textbook and the lecture videos. 6 00:00:18,090 --> 00:00:20,475 We'll spend our time in this video then, 7 00:00:20,475 --> 00:00:23,250 looking at some physical capacitors and inductors. 8 00:00:23,250 --> 00:00:26,310 Talking a bit about how these devices store energy, 9 00:00:26,310 --> 00:00:30,380 show you how to identify capacitance and inductance values on physical parts, 10 00:00:30,380 --> 00:00:34,140 and show you how to measure capacitances using your DMM. 11 00:00:34,140 --> 00:00:39,500 Sadly, most affordable DMMs do not have an inductance measurement capability. 12 00:00:39,500 --> 00:00:40,820 So, for this course, 13 00:00:40,820 --> 00:00:45,290 we'll just have to believe the nominal inductance values for any inductors that we use. 14 00:00:45,290 --> 00:00:47,614 First, we'll talk about capacitors; 15 00:00:47,614 --> 00:00:50,030 Typical capacitor construction consists of 16 00:00:50,030 --> 00:00:56,075 two conductive elements separated by a non-conductive material, called a dielectric. 17 00:00:56,075 --> 00:00:59,120 The dielectric prevents current flow from one element 18 00:00:59,120 --> 00:01:02,095 to the other and is characterized by its permitivity, 19 00:01:02,095 --> 00:01:05,275 designated by the Greek letter, epsilon. 20 00:01:05,275 --> 00:01:09,305 If we apply a voltage difference between the two plates, 21 00:01:09,305 --> 00:01:12,170 charges will accumulate on the upper and lower plates. 22 00:01:12,170 --> 00:01:15,845 These will create an electric field between the plates. 23 00:01:15,845 --> 00:01:19,580 The capacitor stores energy in this electric field. 24 00:01:19,580 --> 00:01:24,410 Capacitance is a quantity which tells us how much energy a capacitor can store. 25 00:01:24,410 --> 00:01:27,140 For a capacitor consisting of two parallel plates, 26 00:01:27,140 --> 00:01:30,230 like the one we saw in the previous slide, the capacitance is, 27 00:01:30,230 --> 00:01:33,680 A times epsilon over d. Where A, 28 00:01:33,680 --> 00:01:35,840 is the cross-sectional area of the plates, 29 00:01:35,840 --> 00:01:38,660 d is the spacing between the plates, 30 00:01:38,660 --> 00:01:41,995 and epsilon is the permittivity of the dielectric. 31 00:01:41,995 --> 00:01:46,415 So, we can increase the capacitance by increasing the cross-sectional area, 32 00:01:46,415 --> 00:01:49,910 decreasing the spacing, or increasing the permittivity. 33 00:01:49,910 --> 00:01:53,180 Now, let's take a look at a few physical capacitors, 34 00:01:53,180 --> 00:01:56,575 measure their capacitance to get a feeling for these relationships. 35 00:01:56,575 --> 00:01:59,405 This is a variable parallel plate capacitor. 36 00:01:59,405 --> 00:02:02,360 The two plates actually consist of multiple plates each. 37 00:02:02,360 --> 00:02:05,340 So, these fins all create one plate, 38 00:02:05,340 --> 00:02:06,990 they're all electrically connected. 39 00:02:06,990 --> 00:02:09,590 The other plate is created by these fins. 40 00:02:09,590 --> 00:02:12,860 The two sets of fins are separated by air gaps between them, 41 00:02:12,860 --> 00:02:14,915 so the dielectric is simply air. 42 00:02:14,915 --> 00:02:17,660 If I turn the knob on the side of the capacitor, 43 00:02:17,660 --> 00:02:20,600 I can increase or decrease the capacitance, 44 00:02:20,600 --> 00:02:24,545 by increasing or decreasing the area of overlap of the conductors. 45 00:02:24,545 --> 00:02:26,810 Let's measure the capacitance and verify that, 46 00:02:26,810 --> 00:02:28,940 that's what actually happens. 47 00:02:28,940 --> 00:02:31,700 To measure capacitance using my DMM, 48 00:02:31,700 --> 00:02:35,420 I plug the leads into the COM and Volt/Ohm ports. 49 00:02:35,420 --> 00:02:40,050 I also connect the leads to the two terminals of the capacitor. 50 00:02:40,580 --> 00:02:43,910 To measure capacitance, I turn my knobs so that 51 00:02:43,910 --> 00:02:47,105 the indicator lines up with the little capacitor symbol. 52 00:02:47,105 --> 00:02:50,450 Currently, there's little or no overlapping area between 53 00:02:50,450 --> 00:02:53,870 these fins and I get about 0.1 nanofarads. 54 00:02:53,870 --> 00:02:55,400 By turning the knob, 55 00:02:55,400 --> 00:02:59,435 I can increase the overlapping area and increase the capacitance. 56 00:02:59,435 --> 00:03:01,865 Now, it's at about 0.4 nanofarads. 57 00:03:01,865 --> 00:03:05,480 If the fins are entirely overlapped, 58 00:03:05,480 --> 00:03:08,470 I get about 0.7 nanofarads. 59 00:03:08,470 --> 00:03:12,065 Now, let's take a look at a very simple homemade capacitor. 60 00:03:12,065 --> 00:03:16,010 My capacitor consists of two wires which are approximately parallel. 61 00:03:16,010 --> 00:03:21,295 They make two conductive elements with a dielectric between them which is currently air. 62 00:03:21,295 --> 00:03:25,500 I can use this property to measure water level. 63 00:03:25,500 --> 00:03:27,800 If I change the permitivity between these, 64 00:03:27,800 --> 00:03:29,435 it'll change the capacitance. 65 00:03:29,435 --> 00:03:33,895 If I insert my wires into this tube of water, 66 00:03:33,895 --> 00:03:36,960 then when I change the water level, 67 00:03:36,960 --> 00:03:40,115 I will also change the capacitance between these wires. 68 00:03:40,115 --> 00:03:41,570 Let's connect our DMM, 69 00:03:41,570 --> 00:03:43,955 change the water level and see how it works. 70 00:03:43,955 --> 00:03:46,699 Now, when the water level is low, 71 00:03:46,699 --> 00:03:50,165 our capacitance is about a half a nanofarad. 72 00:03:50,165 --> 00:03:51,740 Adding some water to this, 73 00:03:51,740 --> 00:03:56,850 increases the water level and should cause the capacitance to go up. 74 00:04:03,170 --> 00:04:08,180 Now, let's look at some typical capacitors which we'll use to create electric circuits. 75 00:04:08,180 --> 00:04:09,665 The capacitors I'll show you, 76 00:04:09,665 --> 00:04:11,840 are from the digital analog parts kit. 77 00:04:11,840 --> 00:04:15,095 The general principles are applicable to most capacitors. 78 00:04:15,095 --> 00:04:17,600 Capacitors are generally described by the type of 79 00:04:17,600 --> 00:04:20,195 dielectric material and their overall construction. 80 00:04:20,195 --> 00:04:22,445 Most of the capacitors in our parts kit 81 00:04:22,445 --> 00:04:24,335 are disc-shaped, like this one. 82 00:04:24,335 --> 00:04:26,150 On these types of capacitors, 83 00:04:26,150 --> 00:04:30,770 the nominal capacitance is encoded as three numbers printed on the capacitor. 84 00:04:30,770 --> 00:04:35,855 These numbers provide a capacitance in picofarads in exponential notation. 85 00:04:35,855 --> 00:04:38,060 The first two numbers are the mantissa of 86 00:04:38,060 --> 00:04:40,610 the number and the third number is the exponent. 87 00:04:40,610 --> 00:04:45,310 For example, this capacitance has the digits 103 printed on it. 88 00:04:45,310 --> 00:04:50,075 This means that its capacitance is 10 times 10 to the third picofarads. 89 00:04:50,075 --> 00:04:53,515 A picofarad is one times 10 to the minus 12 farads. 90 00:04:53,515 --> 00:05:00,395 Therefore, the capacitance of this capacitor is 10 times 10 to the third picofarads, 91 00:05:00,395 --> 00:05:02,990 which is times 10 to the minus 12, 92 00:05:02,990 --> 00:05:10,775 which is equal to 10 times 10 to the minus 9, or 10 nanofarads. 93 00:05:10,775 --> 00:05:15,440 Our actual measured capacitance is about 11 and a half nanofarads. 94 00:05:15,440 --> 00:05:18,590 Electrolytic capacitors are also fairly common. 95 00:05:18,590 --> 00:05:23,075 In electrolytic capacitors, one or both of the conductive plates are not metallic. 96 00:05:23,075 --> 00:05:27,305 These capacitors tend to have a relatively high capacitance for their size. 97 00:05:27,305 --> 00:05:33,100 The electrolytic capacitors in your parts kits are can-shaped rather than disc-shaped. 98 00:05:33,100 --> 00:05:35,175 Electrolytic capacitors are polarized, 99 00:05:35,175 --> 00:05:37,340 that means they don't really work the same way if you 100 00:05:37,340 --> 00:05:39,755 switch the polarity of the voltage at their terminals. 101 00:05:39,755 --> 00:05:43,805 The polarity is indicated by the length of the leads on the capacitor. 102 00:05:43,805 --> 00:05:47,780 The anode has a longer wire than the cathode. 103 00:05:47,780 --> 00:05:52,655 It is intended that the anode always be at a higher voltage than the cathode. 104 00:05:52,655 --> 00:05:54,200 If you reversed the polarity, 105 00:05:54,200 --> 00:05:56,390 the capacitor properties will be different. 106 00:05:56,390 --> 00:05:58,580 In fact, if you apply a voltage in which 107 00:05:58,580 --> 00:06:00,950 the cathode is at a higher voltage than the anode, 108 00:06:00,950 --> 00:06:02,705 the capacitor can explode. 109 00:06:02,705 --> 00:06:04,115 If you do this, by the way, 110 00:06:04,115 --> 00:06:06,095 I recommend that you wear eye protection. 111 00:06:06,095 --> 00:06:08,360 I've personally never blown up a capacitor by 112 00:06:08,360 --> 00:06:11,315 reversing its polarity, but there's a first time for everything. 113 00:06:11,315 --> 00:06:13,580 The electrolytic capacitors in our kit, 114 00:06:13,580 --> 00:06:15,830 are physically large enough so that the capacitance is 115 00:06:15,830 --> 00:06:19,180 printed directly on the side of the capacitor. 116 00:06:19,180 --> 00:06:21,380 This capacitor, for example, 117 00:06:21,380 --> 00:06:24,455 is nominally 220 microfarads. 118 00:06:24,455 --> 00:06:28,400 The printing on the side of the capacitor also provides additional information. 119 00:06:28,400 --> 00:06:32,030 The cathode is indicated by a white stripe with a minus sign on 120 00:06:32,030 --> 00:06:36,065 it and the maximum allowable safe voltage is also printed out on the side. 121 00:06:36,065 --> 00:06:39,290 This capacitor's rated voltage is 10 volts. 122 00:06:39,290 --> 00:06:41,720 Now, let's talk a bit about inductors. 123 00:06:41,720 --> 00:06:44,895 Inductors like capacitors store electrical energy. 124 00:06:44,895 --> 00:06:49,085 Unlike capacitors, inductors store energy in a magnetic field. 125 00:06:49,085 --> 00:06:54,599 Typical inductors are constructed by winding a conductive wire around a central core. 126 00:06:54,599 --> 00:06:56,520 When current runs through the coil, 127 00:06:56,520 --> 00:06:58,515 a magnetic field is created. 128 00:06:58,515 --> 00:07:01,190 The inductance of the inductor is indicative 129 00:07:01,190 --> 00:07:03,920 of the amount of energy that can be stored by the inductor. 130 00:07:03,920 --> 00:07:06,980 The inductance is typically related to the number of turns 131 00:07:06,980 --> 00:07:10,165 the coil takes around the central core and the core material. 132 00:07:10,165 --> 00:07:14,585 Ferrite core materials typically result in relatively high inductance. 133 00:07:14,585 --> 00:07:16,760 Here's a very simple homemade inductor, 134 00:07:16,760 --> 00:07:19,205 I've simply wrapped wire around a carriage bolt. 135 00:07:19,205 --> 00:07:21,440 If I connect a voltage source to the wire, 136 00:07:21,440 --> 00:07:25,475 current will flow through the wire and a magnetic field will be created. 137 00:07:25,475 --> 00:07:28,340 To create a fairly large magnetic field, 138 00:07:28,340 --> 00:07:29,645 I'll need a high current. 139 00:07:29,645 --> 00:07:32,480 So, I'll use the six-volt batteries as my power source. 140 00:07:32,480 --> 00:07:35,000 I know I have a magnetic field because I can pick up 141 00:07:35,000 --> 00:07:38,345 screws with my newly created electromagnet. 142 00:07:38,345 --> 00:07:41,645 Inductors come in a wide range of shapes and sizes. 143 00:07:41,645 --> 00:07:45,740 This is a large high current inductor, about 120 millihenries. 144 00:07:45,740 --> 00:07:48,500 The analog parts kit contains two inductors; 145 00:07:48,500 --> 00:07:51,715 a one millihenry inductor and a one microhenry inductor. 146 00:07:51,715 --> 00:07:55,220 The millihenry inductor is encoded with the numerals 102 on 147 00:07:55,220 --> 00:07:59,300 the side, and the microhenry inductor has the numerals 1R0. 148 00:07:59,300 --> 00:08:02,670 These are both ferrite core inductors.