what conducts

This Lesson Plan is copyright © 2016 by Dr. Jeremy Smith, Tucent Scientific, LLC, and the text may not be modified without prior consent of the Author.

Comments, questions, corrections and other feedback on this Lesson Plan are warmly welcomed at www.TucentScientific.org.

Complimentary Lesson Plan & Teacher’s Guide

What Conducts?

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CONTENTS

Overview & Learner Outcomes ............................................................................................................................................... 3

Next-Generation Science Standards ....................................................................................................................................... 3

Engagement ............................................................................................................................................................................ 4

Invention ................................................................................................................................................................................. 4

Exploration .............................................................................................................................................................................. 5

Closure .................................................................................................................................................................................... 5

Writing Across the Curriculum ................................................................................................................................................ 6

Key Terms ................................................................................................................................................................................ 6

Teacher’s Guide ...................................................................................................................................................................... 7

Current, Voltage, Sources and Sinks ................................................................................................................................... 7

Safety with Electricity ......................................................................................................................................................... 8

Potential and Kinetic Energy, Conductivity, and Resistance ............................................................................................... 8

Setting Up the Activity ........................................................................................................................................................ 9

Learning Styles, Group Discussion, and Writing Across the Curriculum ........................................................................... 10

Questions for Discussion and Journaling .......................................................................................................................... 10

A Note About “Signal” Speed vs. Electron Speed ............................................................................................................. 10

Electricity isn’t due to the movement of electrons through a wire .............................................................................. 11

The electric field travels over a wire at approximately the speed of light ................................................................... 11

Sometimes the field doesn’t travel through the whole wire ........................................................................................ 11

Electrons don’t travel through a wire at the speed of light .......................................................................................... 11



Complimentary Lesson Plan

What Conducts?

Age/grade level: Pre-K (with age-appropriate modification), K-5 Theme: Forces of nature: Electricity and electronics – current, circuits, conductors, and insulators

Energy transformations and work – electricity (a form of potential energy) moves in a closed loop and can be transformed into kinetic energy in the form of light, sound, heat, and others

Description: Students build a simple testing device to determine whether (safe amounts of) electricity flows easily through various materials, then identify the materials as conductors or insulators.

Setting: Tables with testing stations; group circle for discussion. Key terms: current, conductor, insulator, circuit, hypothesis

Materials: Per student or per partnered pair: 1 CR-2032 battery 2 wires with ends stripped of insulation 1 LED 1 What Conducts? Chart Electrical (recommended) or clear tape Safety scissors

For testing stations: aluminum foil, penny, quarter, bar soap, paper clip, popsicle stick, plastic bag, glass bottle, wet and dry soil For teacher’s station: paper, one or more #2 pencils, preferably #2B; 9V battery, 2 test clips Energy Ball (e.g., Safari Ltd. Energy Ball, $8)

Overview & Learner Outcomes Students develop an understanding of electric circuits and electrical conduction by building a continuity tester and using it to investigate the conductivity of common materials. By the end of this activity, students will:

Be able to describe a circuit as a loop in which electricity flows. Be able to identify, compare, and contrast conductors and insulators. Be able to document their experimental progress (a yes/no chart).

We have endeavored to make this activity rewarding across learning styles in the spirit of Gardner’s Multiple Intelligences Theory. More guidance on adapting the activity for various learning styles can be found in the attached Teacher’s Guide.

Next-Generation Science Standards

ETS1.A A situation that people want to change or create can be approached as a problem to be solved through

engineering. Such problems may have many acceptable solutions. K-PS2-2 Analyze data from tests of an object or tool to determine if it works as intended. K-PS3-1 Make observations (firsthand or from media) to collect data that can be used to make comparisons. K-PS3-2 Use tools and materials provided to design and build a device that solves a specific problem or a solution to a

specific problem. K-LS1-1 Use observations (firsthand or from media) to describe patterns in the natural world in order to answer

scientific questions.

Tucent Scientific Complimentary Lesson Plan: What Conducts? –



Engagement

As a group, discuss what electricity is, how humans use it, and how to deal with it safely (see the attached Teacher’s Guide for discussion points and tips). You can then complete the following activity as a group to demonstrate that electricity travels in a closed loop.

1. Introduce the Energy Ball: tell the children that it contains a battery that “makes” (actually, stores) electricity, a metal contact where the electricity exits the ball, and another contact where the electricity re-enters the ball. When electricity flows, it is called an electrical current.

2. Explain that the group will “become” an electric circuit, a loop through which electrical current flows. Make sure the students understand that this current will not hurt them, and, in fact, there is so little electricity coming from the tiny battery inside the Energy Ball that it is impossible to even feel it (students making contact with the Energy Ball will feel the vibration from the vibro-motor inside it, but you can explain that they are not feeling the electricity itself).

3. Have the group stand in a circle, touching fingertip to fingertip. Your finger should be on one contact and the person to the right of you should have their finger on the other. The ball will light up and make noise.

4. Break the loop a few times to demonstrate that electricity has to have a complete loop (circuit) in order to flow. Ask the students what they discovered through the Energy Ball activity. Students should understand:

Where the electricity comes from (the battery inside the Energy Ball) Where the electricity goes (the opposite side of the battery); and The path the electricity takes (out of the battery, through the lights and buzzer inside the Energy Ball, through the

students themselves, and back into the Energy Ball). The students should now have an idea that the flow of electricity, or current, has to come from somewhere and return somewhere in order to flow – that is, it has to form a “closed” circuit. It might be useful to draw an analogy with water from a faucet that drains from the sink, but instruct the students to imagine an unusual faucet that won’t turn on unless the drain is unplugged! As an aside: in physics and engineering, we do refer to energy “sources” and “sinks.” In this case, the (+) side of the CR2032 battery is the electricity source and the underside is its sink (see the attached Teacher’s Guide for a deeper understanding of sources and sinks). It’s appropriate to discuss electricity safety here. We recommend the following guidelines, modified, of course, for age appropriateness:

1. We are using small batteries for this activity, which are very safe, but they can still get very hot or ruined if you connect a wire directly from the (+) side to the underside of the battery. Batteries want to be useful. You should always have a light, a buzzer, or something else to soak up the battery’s electricity.

2. Batteries are like balloons: the bigger they are, the more electricity they can hold. Batteries as big as the ones in your parents’ cars can hold a lot of electricity and hurt you very badly. Never play with big batteries!

3. Wall outlets have a lot of electricity. Never touch them with your hands, and never, ever put anything in a wall outlet other than a plug!

4. Too much electricity can also damage electronic parts. (If you like, you can demonstrate this by putting an extra LED across the two terminals of your 9V battery, with the long leg (or lead) of the bulb touching the (+) terminal. The small batteries provide just enough electricity to light the LED (3.3V); the larger 9V battery provides too much. The pop will be small and quick, but not dangerous. We discuss why we use a 9V for the last experiment in the section “Kinetic Energy, Conductivity, and Resistance” in the Teacher’s Guide, but since it will serve as a conversation for the class as a whole at the end of the activity, don’t give it away just yet!)

Invention

Introduction

1. Remind the students that electricity has to come from somewhere (the battery) and go somewhere (the battery) in a closed loop in order to flow.

2. This loop is usually made of metal (wire), but there are other materials that work well, too.




Build the device

Depending on their age, students may need assistance with building the “testing device” (actually a continuity tester).

1. Attach one wire to each face of the battery. If you have twisted wire, it may help to untwist the wires and fan them out so they’re flat (see the Teacher’s Guide for an illustration). Secure the wires with a single piece of tape.

2. Twist the wire attached to the battery’s (+) face around the long metal leg (“lead”) of the LED. These, too, can be secured with tape, if desired.

3. Have the students confirm that their “device” works by touching the loose wire to the short lead of the LED. 4. Now students can use the unattached LED lead and wire for testing.

Exploration

3V Stations

1. Instruct the students that they are testing different materials to determine whether electricity can flow through the materials easily. They should not touch the loose wire and short LED lead together directly, but rather touch both to the material a short distance – perhaps the width of a fingernail – apart. You can demonstrate this on one conductor (e.g., aluminum foil) and one insulator (e.g. popsicle stick).

2. The students will be recording their results on the yes/no “What Conducts?” chart. They should make a guess (hypothesis) in the left column before testing the material. The recording method can be age-appropriate: if they expect the material to pass electricity and otherwise; or or ; yes/no; or conductor/insulator – but the system should be consistent and meaningful to the student.

3. The student should record their result in the right column after testing the material. Techer’s Station (9V Graphite Circuit)

1. At the last station, demonstrate that circuits can be drawn on ordinary paper with a #2 pencil and allow the child and partner to create their own circuits in pencil. Lines don’t need to be dark but should be wide, and they shouldn’t cross.

2. Allow the child to try his/her 3V apparatus first, then the 9V apparatus, which stays at the station. Make sure the student is keeping the two leads separated – otherwise, the 9V battery will pop the LED (which isn’t dangerous, but might frustrate the student).

3. The 3V battery will not work, but the 9V will. Ask why.

This is the ONLY part of the experiment where the 9V will be used. It is ordinarily too powerful for an LED, but since the pencil’s graphite has such high resistance, it’s just enough “juice” to work here.)

Closure

As a class, discuss the concepts presented in the lesson:

1. Electricity must travel in a loop (a circuit) or it won’t flow. 2. Electricity flows through some materials but not others. If electricity flows easily through a material, the material is

called a conductor; if it doesn’t, it is called an insulator. 3. If the electricity has enough “oomph” behind it (voltage: see Teacher’s Guide), it will make it through any material. This

is why the 9V battery can “pull” electricity through “pencil lead” (graphite) when the 3V battery couldn’t, and why electricity can travel through the air as lightning, but not in the tiny amounts of electricity we’ve used today (refer to the section “Potential and Kinetic Energy, Conductivity, and Resistance” in the Teacher’s Guide for more on this topic).

You may want to recap the discussion of electricity safety at this point. Here are those guidelines again:







4. Too much electricity can also damage electronic parts. (If you like, you can demonstrate this by putting an extra LED across the two terminals of the 9V battery, with the long leg (or lead) of the bulb touching the (+) terminal. The small batteries provide just enough electricity to light the LED (3.3V); the larger 9V battery provides too much. The pop will be small and quick, but not dangerous. We discuss why we use a 9V for the last experiment in the section “Potential and Kinetic Energy, Conductivity, and Resistance” in the Teacher’s Guide, but since it will serve as a conversation for the class as a whole at the end of the activity, don’t give it away just yet!)

The Writing Across the Curriculum topics below can also be used to guide group discussions. Some of the questions are more appropriate for older students.

Writing Across the Curriculum

What is the potential energy in our experiment? Here’s a hint: we used 3V (three volt) and 9V (nine volt) batteries in our experiment. Which battery was better at “pulling” electricity through the pencil markings? Why do you think that is? What do you think “volts” or “voltage” means?

You may have heard that “energy can neither be created nor destroyed.” This is called the Law of Conservation of Energy. Conservation of Energy means that the energy we use to light our homes has to be produced somewhere, such as from water, wind, the sun, and gasoline or oil, and is either used up or released as a different kind of energy. Rub your hands together quickly. The energy produced in your body that you use to rub your hands together goes into making the rubbing sound, or into the effort of pushing your hands apart, or into heating up your palms! Think about the pencil experiment. If just enough electricity (energy) was going through the pencil scribbles to dimly light your bulb, where was the rest of the energy going? Where is the kinetic energy in our experiment?

If electricity only travels in a closed loop, why does lightning seem to travel between the clouds and the ground?

When a major earthquake knocked out power to Los Angeles, California, in 1994, the Griffith Observatory started receiving calls from people asking why the sky looked so strange, and whether it had anything to do with the earthquake. There was nothing unusual about the sky – many people had lived in the city for so long, under artificial streetlights and building lights, that when the power went out, people saw the starry, nighttime sky for the first time. How has electricity improved your life and the lives of others? In what ways has it not improved our lives? What could we do in the future to solve these problems, without losing the benefits of electricity?

If connecting a wire between the top and bottom of a battery, with nothing in between to soak up energy, makes the battery get hot and possibly burst, why don’t batteries burst all the time, just by sitting on a shelf?

Key Terms

Current – the flow of electricity. Scientists and engineers can measure this current.

Conductor – a material through which electricity flows easily.

Insulator – a material that resists the flow of electricity.

Circuit – a “loop” through which current flows. A circuit has something that stores or produces energy, like a battery; something to use the energy, like a bulb or a motor; and a place for the energy to go, like the other end or side of the battery. It also needs something to connect these parts. That “something” is usually a metal wire, but, as we’ve seen, it can be made of other things, too!

Hypothesis – a statement of what will happen if something is really true. A hypothesis is based on how we believe things work (a theory about something) and lets us make a prediction that something will happen or not. For example, we might have a theory that fire is hot. That leads us to a hypothesis that heat will make other things hot, and we predict that a flame will burn paper. (But we should let an adult test this prediction!) A hypothesis is not always correct. We have to make predictions and test it to find out if it is.

Tucent Scientific Complimentary Lesson Plan: What Conducts? Teacher’s Guide –



Complimentary Lesson Plan

What Conducts?

Teacher’s Guide

What Conducts?: Students develop an understanding of electric circuits and electrical conduction by building a continuity tester and using it to investigate the conductivity of common materials.

By the end of this lesson, students will: Be able to describe a circuit as a loop in which electricity flows. Be able to identify, compare, and contrast conductors and insulators. Be able to document their experimental progress (a yes/no chart).

We have endeavored to make this activity rewarding across learning styles in the spirit of Gardner’s Multiple Intelligences Theory. More guidance on adapting the activity for various learning styles can be found at the end of this Teacher’s Guide.

Electricity is everywhere. Early experiments with electricity in the eighteenth, nineteenth, and even early twentieth centuries were met by the public with a sense of awe; inventors and scientists such as Edison, Galvani, and Tesla were regarded almost as magicians in their time. Today, it is so commonplace that we in the developed world only think about electricity hen the power goes out.

For high school students and adults, electricity can be described as the flow of electrons that have been freed from their parent atoms. In metals, electrons spend less time surrounding an atom’s nucleus and more time “smeared” around all the atoms in the metal, or at least the atoms in their immediate “neighborhood.” This characteristic makes it easier to “pull” the electrons away from the atomic nuclei and use them to do work. For younger students, it may be sufficient – or even necessary, if they have never been exposed to the concept of atoms – to treat “electricity” as a “Force of Nature” without delving into electrons and their origin.

Current, Voltage, Sources and Sinks

For the purposes of the What Conducts? Activity, we refer to the flow of electricity as electrical current, which is absolutely correct; however, scientists and engineers quantify this current by the number of electrons that would be flowing past some point in a given amount of time. Current is counted in terms of amperes or amps; a device that needs 1A of electricity is pulling over six quintillion (6 billion billions, or 6 followed by 18 zeroes) electrons every second. As unimaginably large as that number is, a typical car headlight pulls nine times that amount, or nearly 56 quintillion electrons, every second. Even tiny LED bulbs, found in many flashlights, typically pull 20mA, or 20/1000th of an ampere, or 12 quadrillion electrons, per second. This is more electrons used per second than there are stars in the Andromeda Galaxy, or, more accurately, in twelve thousand Andromeda Galaxies.

And yet, not a single electron will move if it has nowhere to go.

As parents and teachers, we know how difficult it can be at times to get our children moving, but a trip to an amusement park empties a busload of children very quickly, if not somewhat chaotically! Free electrons are similarly unmotivated when it comes to “doing work,” but, like children, we can generally think of them as thrill-seekers: the taller the water slide, the more




motivated they are to get going. In the case of electricity, we call this “motivation” voltage – in fact, the voltage present in an electrical circuit was historically called the electromotive force. Voltage is only present between two points with different levels of energy, or potential. For example, a water slide that was very high, but also very flat, or even very close to the ground, but also very flat, would be very unmotivating to ride – it is, after all, the thrill of the drop that excites us, makes the water move faster, and gives energy to the giant splash at the bottom that wets spectators. That’s why a current will only flow between two battery terminals in a closed loop: the positive terminal of a battery, like the high point of a water slide, is the source of the current, its highest potential, whereas the negative terminal lacks electrons, is the end of the ride and its lowest potential, and so serves as a current sink.

Safety with Electricity

Scientists and engineers are fond of saying that it’s current, not voltage, that presents a danger to humans. In a way, that’s true: a shock from an electric fence (8,000V) certainly hurts, and may cramp an animal’s muscles, but are designed with low current (around 120mA, or 120/1000th of an ampere) so as not to kill even small animals. An electrical eel can emit up to 860V and 1A for a very short time to stun or kill prey, but it doesn’t apply the current long enough to kill an adult human.

But this is oversimplifying a bit. An average 12V car battery only carries a potential difference of 12V between its two terminals – four times more than the batteries we use in What Conducts? – but can discharge between 200A and 1000A through a human body! And “shorting” a battery by placing a wire directly between the two terminals, with no “load” on the wire – that is, work for the electricity to do, such as turning on a light or running a speaker – is the equivalent of chaotically emptying that busful of children at the amusement park: all the current rushes out at once, expending a lot of energy in a very short time. With electricity, this excess energy is wasted as heat, which can make the battery very hot or even burst the metal casing.

We therefore recommend giving your students the following guidelines for electrical safety, modified, of course, for age appropriateness:




Potential and Kinetic Energy, Conductivity, and Resistance

In reality, any material can act as a conductor or insulator depending on the voltage and current involved. Based on our water slide analogy, you’ve probably already figured out that there is a relationship between potential energy and voltage. If so, you’re right: just like higher water slides have greater gravitational potential energy, an energy source or storage device (battery) with a higher voltage rating has a greater electrical potential energy – in fact, voltage is electrical potential energy.

Another way to look at voltage is through the relationship between voltage (the height of the water slide) and current (the number of riders – electrons, in our case). Let’s ignore how many riders are getting on the ride and think about what happens before they go down the hill.

We know that riders at the top of the water slide have a certain amount of potential energy based on the height of the slide (that’s our voltage), but let’s add a jam of stuck riders near the top resisting the flow and imagine a very wide slide. If it isn’t a total blockage on our wide slide, a few riders can still get past; with a larger blockage, fewer riders can pass. Air acts like a jam of riders in the middle of the water slide: it resists the flow. If you have enough potential difference (voltage) across the jam, like a higher starting point on the slide, riders would have enough energy to break through the jam. With electricity, we see this as a spark across an air gap. It takes an enormous difference in potential between two points to jump an air gap, however. Under average circumstances – rain, humidity, dust in the air – lightning requires about 4,500 to 5,500 volts’ worth of potential difference between cloud and ground in order to advance. All that excess energy also generates a lot of heat (36,032°F or 20,000°C, which is three times hotter than the surface of the sun!) and shock waves (thunder) as waste. For our tiny battery voltages (1-3 volts), an air gap is an impenetrable jam in the current. The “circuit” formed by lightning occurs through charge buildup between the clouds and ground.

Air isn’t the only material that serves to resist the flow of electricity. In fact, all materials resist or pass electricity to some degree. Some materials – like copper, silver, aluminum, and salt water – let electrons through fairly easily, and we call these




materials conductors as a convenient shorthand. Others – paper, glass, rubber – resist electrons under our usual, everyday circumstances, and we call them insulators. But in reality there are no perfect conductors or perfect insulators. As is the case with a rider jam on our water slide, an electron source with enough potential energy, or voltage, and/or enough riders, or current, can break through the jam, and we get a blown speaker, burnt-out light, or an electrical spark, like lightning. Engineers call this insulator breakdown. Our graphite (pencil lead) experiment is a good example of this. Graphite resists electrons that have only 3.3V of electrical potential energy behind them – that’s the voltage of our watch battery – but with 5.2V more “oomph” behind them (our 9V battery), the electrons have enough potential energy to travel through the resistance of the graphite, and the bulb glows a bit.

Scientists and engineers can quantify how good of a conductor or insulator a material is. This is usually defined as resistance, which is measured in ohms; a material that has ohm of resistance “takes up” 1V of potential energy for every 1 ampere, or 6 billion billion electrons per second. We can also flip this around and talk about how many electrons per second are jammed for every 1V of potential energy. This is called conductance. Conductance and resistance are just inverses of each other.

You’re probably also aware that “energy can neither be created nor destroyed.” In practice, this means that potential energy can be traded for kinetic energy, or vice versa, but energy can’t just appear or disappear. So where is the “lost” energy going when impeded by some resistance? The answer, as you might have guessed, is that our potential energy (voltage) is being converted to kinetic energy. In an electrical circuit, kinetic energy takes the form of heat – something akin to the jammed electrons rubbing against each other and generating heat from friction. (Electrons don’t really exhibit friction in the way we normally think of it, but that’s beyond the scope of this Guide.)

Setting Up the Activity

1. You should have two wires (preferably different colors), 1 CR2035 watch battery, and 1 LED. 4” wires are best for small hands. Strip off ¾” insulation from each end.

2. Have the students untwist the wires and fan them out. There’s no need for perfection here.

3. So that everyone is on the same page, the red wire should go on the (+) side of the battery and the black wire on the underside.

4. Wrap with tape (electrical tape is best; painter’s tape used here for clarity) and smooth the tape around the wires.

5. Wrap the other end of the red wire around the LONG LEG of the LED.

6. Students should keep a fingernail to a half-fingernail’s width between the two leads for testing.

7. Some students may have luck with the 3.3V battery during the graphite activity. If so, have them draw longer marks so there is a wider distance between the two leads, then try again with the 9V battery.




Learning Styles, Group Discussion, and Writing Across the Curriculum

Psychological research has sustained the idea that individual humans’ intelligence and talents aren’t general; instead, individuals exhibit different talents and abilities, preferred ways of learning, and personalized perspectives and interest with respect to the world around them. According to this Theory of Multiple Intelligences, a given student may excel at learning through one or more of the following methods:

Visual/Spatial Drawing, diagrams, exploration through spatial puzzles, photographs, and videos

Kinesthetic Movement, invention, building, acting out ideas and role playing Aural/Musical Rhythms (including rhythmic poetry), rhyming, sound, lyrics Interpersonal Group or partner activities, dialogue, writing letters, explaining concepts

and methods to others Intrapersonal Introspection, journaling, creative materials Naturalistic Classification, attention to environment, outdoor learning, noting natural

changes and patterns Verbal/Linguistic Reading, word games, vocabulary, lectures, storytelling Logical/Mathematical Experimentation, logic games, mysteries, puzzles, highlighting patterns

and relationships

Questions for Discussion and Journaling

What is the potential energy in our experiment? Here’s a hint: we used 3V (three volt) and 9V (nine volt) batteries in our experiment. Which battery was better at “pulling” electricity through the pencil markings? Why do you think that is? What do you think “volts” or “voltage” means?

You may have heard that “energy can neither be created nor destroyed.” This is called the Law of Conservation of Energy. Conservation of Energy means that the energy we use to light our homes has to be produced somewhere, such as from water, wind, the sun, and gasoline or oil, and is either used up or released as a different kind of energy. Rub your hands together quickly. The energy produced in your body that you use to rub your hands together goes into making the rubbing sound, or into the effort of pushing your hands apart, or into heating up your palms! Think about the pencil experiment. If just enough electricity (energy) was going through the pencil scribbles to dimly light your bulb, where was the rest of the energy going? Where is the kinetic energy in our experiment?

If electricity only travels in a closed loop, why does lightning seem to travel between the clouds and the ground?

When a major earthquake knocked out power to Los Angeles, California, in 1994, the Griffith Observatory started receiving calls from people asking why the sky looked so strange, and whether it had anything to do with the earthquake. There was nothing unusual about the sky – many people had lived in the city for so long, under artificial streetlights and building lights, that when the power went out, people saw the starry, nighttime sky for the first time. How has electricity improved your life and the lives of others? In what ways has it not improved our lives? What could we do in the future to solve these problems, without losing the benefits of electricity?

If connecting a wire between the top and bottom of a battery, with nothing in between to soak up energy, makes the battery get hot and possibly burst, why don’t batteries burst all the time, just by sitting on a shelf?

A Note About “Signal” Speed vs. Electron Speed

A physicist colleague has asked us to dispel a misconception about the speed of the electricity traveling through a wire. This subject gets complicated pretty quickly, but let’s address a couple of these misconceptions in a qualitative way, as briefly and thoroughly as we can. You may want to discuss these points with your students in an age-appropriate way.




Electricity isn’t due to the movement of electrons through a wire. It’s really the electric field, not the electrons themselves, that’s responsible for the phenomena we think of as “electricity.” We’ll introduce the electromagnetic field in another lesson, but for now, you may want to think of it as a gradient of potential energy that travels the length of the wire.

The electric field travels over a wire at approximately the speed of light. Not at the speed of light – that’s only true in the vacuum of empty space – but pretty darned close. The electric field speed is quantified by a velocity factor, and the velocity factor depends on the composition of the conductor. For a typical coaxial cable, used for cable television, it’s about 60-85% the speed of light.

Sometimes the field doesn’t travel through the whole wire. For direct current (dc), which is what we get from a battery, this field travels through the whole conductor (wire) and in the space just outside the conductor, or dielectric. Alternating current (ac), which comes from electrical outlets, only travels through the dielectric and a small section around the outermost surface, or skin, of the conductor – the higher the ac frequency, the less ac current flows through the core of the conductor, and adheres more closely to the skin. In fact, most antennas are made of hollow metal tubes to save weight and cost, since the middle of the conductor isn’t used for high-frequency ac current anyway.

Electrons don’t travel through a wire at the speed of light. Again, it’s the electric field (potential energy) that travels at the speed of light; electrons move much more slowly, and in the case of alternating current, they barely move at all! How slowly, though, is a complicated question. Electrons whizz around the nucleus of their parent atom at about 1% the speed of light – 1,367 miles per hour – still fast enough to go around the earth in 18 seconds and change. In metals, there’s a value called the drift velocity, which is something on the order of a few millimeters per second, but that’s based on an idealized model of electrons and their effects on the related magnetic field, and isn’t appropriate in practice, either. Confused? You’re not alone. Even experienced physicists and engineers disagree about these things. It’s further complicated by the fact that electrons aren’t solid balls, or dots, or marbles, or anything else we’re familiar with in everyday life – they’re both solid particles and smeared-out waves.

what conducts

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