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>> In this video, we'll introduce some of

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the practical aspects of capacitors and inductors.

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As usual in the lab videos,

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I'll assume that you're getting the theoretical information about

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these devices from the textbook and the lecture videos.

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We'll spend our time in this video then,

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looking at some physical capacitors and inductors.

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Talking a bit about how these devices store energy,

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show you how to identify capacitance and inductance values on physical parts,

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and show you how to measure capacitances using your DMM.

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Sadly, most affordable DMMs do not have an inductance measurement capability.

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So, for this course,

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we'll just have to believe the nominal inductance values for any inductors that we use.

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First, we'll talk about capacitors;

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Typical capacitor construction consists of

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two conductive elements separated by a non-conductive material, called a dielectric.

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The dielectric prevents current flow from one element

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to the other and is characterized by its permitivity,

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designated by the Greek letter, epsilon.

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If we apply a voltage difference between the two plates,

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charges will accumulate on the upper and lower plates.

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These will create an electric field between the plates.

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The capacitor stores energy in this electric field.

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Capacitance is a quantity which tells us how much energy a capacitor can store.

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For a capacitor consisting of two parallel plates,

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like the one we saw in the previous slide, the capacitance is,

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A times epsilon over d. Where A,

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is the cross-sectional area of the plates,

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d is the spacing between the plates,

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and epsilon is the permittivity of the dielectric.

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So, we can increase the capacitance by increasing the cross-sectional area,

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decreasing the spacing, or increasing the permittivity.

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Now, let's take a look at a few physical capacitors,

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measure their capacitance to get a feeling for these relationships.

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This is a variable parallel plate capacitor.

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The two plates actually consist of multiple plates each.

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So, these fins all create one plate,

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they're all electrically connected.

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The other plate is created by these fins.

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The two sets of fins are separated by air gaps between them,

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so the dielectric is simply air.

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If I turn the knob on the side of the capacitor,

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I can increase or decrease the capacitance,

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by increasing or decreasing the area of overlap of the conductors.

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Let's measure the capacitance and verify that,

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that's what actually happens.

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To measure capacitance using my DMM,

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I plug the leads into the COM and Volt/Ohm ports.

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I also connect the leads to the two terminals of the capacitor.

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To measure capacitance, I turn my knobs so that

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the indicator lines up with the little capacitor symbol.

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Currently, there's little or no overlapping area between

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these fins and I get about 0.1 nanofarads.

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By turning the knob,

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I can increase the overlapping area and increase the capacitance.

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Now, it's at about 0.4 nanofarads.

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If the fins are entirely overlapped,

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I get about 0.7 nanofarads.

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Now, let's take a look at a very simple homemade capacitor.

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My capacitor consists of two wires which are approximately parallel.

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They make two conductive elements with a dielectric between them which is currently air.

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I can use this property to measure water level.

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If I change the permitivity between these,

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it'll change the capacitance.

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If I insert my wires into this tube of water,

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then when I change the water level,

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I will also change the capacitance between these wires.

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Let's connect our DMM,

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change the water level and see how it works.

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Now, when the water level is low,

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our capacitance is about a half a nanofarad.

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Adding some water to this,

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increases the water level and should cause the capacitance to go up.

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Now, let's look at some typical capacitors which we'll use to create electric circuits.

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The capacitors I'll show you,

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are from the digital analog parts kit.

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The general principles are applicable to most capacitors.

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Capacitors are generally described by the type of

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dielectric material and their overall construction.

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Most of the capacitors in our parts kit

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are disc-shaped, like this one.

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On these types of capacitors,

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the nominal capacitance is encoded as three numbers printed on the capacitor.

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These numbers provide a capacitance in picofarads in exponential notation.

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The first two numbers are the mantissa of

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the number and the third number is the exponent.

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For example, this capacitance has the digits 103 printed on it.

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This means that its capacitance is 10 times 10 to the third picofarads.

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A picofarad is one times 10 to the minus 12 farads.

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Therefore, the capacitance of this capacitor is 10 times 10 to the third picofarads,

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which is times 10 to the minus 12,

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which is equal to 10 times 10 to the minus 9, or 10 nanofarads.

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Our actual measured capacitance is about 11 and a half nanofarads.

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Electrolytic capacitors are also fairly common.

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In electrolytic capacitors, one or both of the conductive plates are not metallic.

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These capacitors tend to have a relatively high capacitance for their size.

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The electrolytic capacitors in your parts kits are can-shaped rather than disc-shaped.

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Electrolytic capacitors are polarized,

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that means they don't really work the same way if you

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switch the polarity of the voltage at their terminals.

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The polarity is indicated by the length of the leads on the capacitor.

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The anode has a longer wire than the cathode.

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It is intended that the anode always be at a higher voltage than the cathode.

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If you reversed the polarity,

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the capacitor properties will be different.

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In fact, if you apply a voltage in which

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the cathode is at a higher voltage than the anode,

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the capacitor can explode.

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If you do this, by the way,

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I recommend that you wear eye protection.

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I've personally never blown up a capacitor by

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reversing its polarity, but there's a first time for everything.

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The electrolytic capacitors in our kit,

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are physically large enough so that the capacitance is

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printed directly on the side of the capacitor.

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This capacitor, for example,

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is nominally 220 microfarads.

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The printing on the side of the capacitor also provides additional information.

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The cathode is indicated by a white stripe with a minus sign on

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it and the maximum allowable safe voltage is also printed out on the side.

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This capacitor's rated voltage is 10 volts.

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Now, let's talk a bit about inductors.

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Inductors like capacitors store electrical energy.

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Unlike capacitors, inductors store energy in a magnetic field.

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Typical inductors are constructed by winding a conductive wire around a central core.

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When current runs through the coil,

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a magnetic field is created.

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The inductance of the inductor is indicative

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of the amount of energy that can be stored by the inductor.

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The inductance is typically related to the number of turns

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the coil takes around the central core and the core material.

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Ferrite core materials typically result in relatively high inductance.

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Here's a very simple homemade inductor,

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I've simply wrapped wire around a carriage bolt.

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If I connect a voltage source to the wire,

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current will flow through the wire and a magnetic field will be created.

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To create a fairly large magnetic field,

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I'll need a high current.

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So, I'll use the six-volt batteries as my power source.

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I know I have a magnetic field because I can pick up

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screws with my newly created electromagnet.

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Inductors come in a wide range of shapes and sizes.

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This is a large high current inductor, about 120 millihenries.

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The analog parts kit contains two inductors;

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a one millihenry inductor and a one microhenry inductor.

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The millihenry inductor is encoded with the numerals 102 on

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the side, and the microhenry inductor has the numerals 1R0.

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These are both ferrite core inductors.