Electrical Energyids 101

ELECTRICAL ENERGYIDS 101

Electricity is a mainstay of modern life. We flip a switch and lights come on “as if by magic.” We touch a computer screen and images move instantly at our command. It is easy to forget that all of these things involve work and thus consume energy.

In your daily life, if you need some electrical energy where are you likely to get it? If you just think about nearby places in your home or the classroom, where does our electrical energy seem to come from? (Most people come up with two common answers and which one they happen to use usually depends on how they are using the energy.)

All of the electrical energy we use in our technological lives ultimately comes from electrical generators. In western Washington, the electric outlets in our walls get most of their energy directly from generators in hydroelectric dams with names like Diablo and Grand Coulee. We also get electrical energy from generators in windmills, a nuclear plant, and a coal or oil plant here and there.

“Wait a minute. I thought the stuff we got from the dams was electrical power. What’s the difference between power and energy?”

Good question. Some more vocabulary may be needed.

Energy: the ability to do work. This is what we’ve been studying.
Power: the rate at which we do work, consume energy, or produce energy (depending on how the word is used). For example, if Jack slowly walks up a hill carrying a heavy pail and Jill runs up the same hill with an identical pail, then they both did the same amount of work on their pails. They used the same amount of energy. Jill used her energy more quickly so she used more power while she was doing it. She increased the energy of her pail by the same amount but she did it in less time so she delivered (and consumed) more power while she was running. She then waited for Jack who was continuing to slowly deliver energy to his pail long after the energy of Jill’s pail had stopped increasing.

The relationship between energy and power is the same as the relationship between distance and speed. Two people can travel the same distance at different speeds. On the other hand, if they keep moving for the same amount of time then the one with the greatest speed will cover the greatest distance. In this analogy, energy is like the distance traveled and power is like the speed in which it is done.

When we use batteries for electrical energy, we are simply making use of a convenient way of storing electrical energy that was generated elsewhere.

For the first electrical experiment you will need:

A wire (and only one)
A light bulb
An electrical “cell” (Most people call this a battery. When you buy one AA “battery” you are really buying one cell. Technically speaking a battery is more than one cell connected together. In daily language very few people use these words correctly so it is okay to call it a battery, but now you know.)

Now the experiment: light the light bulb. That’s it. With no other equipment than the cell and a wire, get the bulb to light up. It is often hard to hold all of the pieces in precisely the right way so you may work with your classmates. Once you have successfully lit a bulb, you may draw a sketch of what you did below. Notice there is more than one space for a sketch. That’s because there is more than one way to do this. You might try to find some other ways.

For the next electrical experiments you will need:

An electrical kit with wires, light bulbs, andbulb holders.
A set of “cells” or “batteries” (or whatever you want to call them)

Please be kind to the equipment! When people get an electrical kit in their hands it is extremely tempting to start playing by connecting things in all kinds of crazy ways. That’s good. That’s how people learn, but we need you to follow instructions with this equipment! Only connect the equipment in ways that we tell you to connect it. Otherwise it is too easy to damage the equipment and we do not have a lot of money for replacement costs. Thank you.

Step 1: Light a light bulb using just one cell but this time you may use two wires and a bulb holder (“socket”) as well. Much easier, huh?

Now look at the equipment:

You have two kinds of light bulbs. Some are longer and some are rounder. We can call them “long” and “round” to tell them apart. For these experiments it is only important that you use only one kind of bulb. They should be all long or all round. Don’t mix both kinds in the same experiment (yet).
Your battery holder has metal screws which allow you to connect wires anywhere. If you connect wires to your battery holder, only the cells between the two wires will be used. You can leave the other cells in the battery holder and they can just chill for a while (those words may be more appropriate than you realize).

For the next experiments we will use only the long bulbs and only two cells (so you will connect your wires with only two cells between them).

More vocabulary:

Electric charge or just charge: Charge is what moves in wires and causes bulbs to light and motors to move. In a river, the stuff that moves downstream is called water.
Electric current or just current: Current is the motion of the charge, specifically it is how much charge passes by per second. The same word applies to rivers. If a leaf falls on a river, we say it is carried away by the current. The current in a stream might be measured in gallons per second. The current in a wire is a measure of “charge per second” and it is measured in units called amps.
Series: Two (or more) things are in series if all of the current that flows through one has to flow through the other one as well. Imagine a movie theater where you buy a ticket, enter through a door, hand the ticket to a ticket-taker, and then walk through a turnstile. The ticket counter, the door, the ticket-taker, and the turnstile are all in series. If there is a long line of people, all of the people have to go through all four steps in series.
Parallel: Two (or more) things are in parallel if things can pass through one or the other with the same “pressure” to get them through. They may or may not have the same amount of stuff (current) flowing through them. For example, a grocery store with many checkout lines will have many cahiers working in parallel. Some may be faster than others and some may work the express lines but they are all working in parallel. Think of a bucket of water with several leaks in the bottom. Water may flow through some leaks faster than others but all of the leaks are in parallel.

Talk with your classmates and try to come up with other examples of “series” and “parallel”.

To shorten the instructions for the next experiments, it will be useful to use schematic (simplified) circuit diagrams. Your instructor should lead a discussion of circuit diagrams at this point. The table below should help you to organize your notes.

Item description / Sketch / Diagram
Light bulb
Cell
Cell lighting one bulb
A battery consisting of two cells in series lighting up three bulbs in series / (you can skip this)
A battery consisting of three cells in series lighting three bulbs in parallel / (you can skip this, too)
(make up your own
if you want) / (you can skip this, too!)

Bulbs in series: For this experiment you will use one, two, or three long bulbs and only two cells (leave the others in the battery holder but don’t connect them in the circuit).

Make each of the following circuits one at a time, starting with the one on the left and inserting another bulb in series each time (without changing the number of cells). Make observations about what happens as you add bulbs in series.

What happens to the brightness of each individual bulb as more bulbs are added in series?

What (would you guess) about the amount of power consumed by each individual bulb as more bulbs are added in series?

What (would you guess) about the total power consumed by the whole circuit as more bulbs are added in series? (Is the answer obvious?)

Bulbs in parallel: For this experiment you will use one, two, or three long bulbs and only two cells (leave the others in the battery holder but don’t connect them in the circuit).

Make each of the following circuits one at a time, starting with the one on the left and inserting another bulb in parallel each time (without changing the number of cells). Make observations about what happens as you add bulbs in parallel.

What happens to the brightness of each individual bulb as more bulbs are added in parallel?

What (would you guess) about the amount of power consumed by each individual bulb as more bulbs are added in parallel?

What (would you guess) about the total power consumed by the whole circuit as more bulbs are added in parallel? (Is the answer obvious?)

Based on what you have seen here, which (would you guess) is a better model of the lights in a house or school, bulbs in series or bulbs in parallel? Explain.

Light bulbs in parallel: Feel the work.

In this experiment we will use only the round light bulbs so make sure you have at least five round bulbs. Also, this experiment requires placing a number of round light bulbs in parallel so you might want a special circuit board designed for that purpose. For this experiment you will also need a hand-held electric generator or “Genecon.”

CAUTION: The hand-held generators are not cheap! It may be tempting to see how much energy you can get out of the generator. We know you are strong enough to burn out light bulbs and break the generator!!! You do not need to prove this. Use the generators with care.

The participants of your group will need to take turns in the various roles of this experiment so you should not have a large group. Three students per group will be fine.

One student will operate the generator. Turn the handle of the generator at a gentle but constant rate. Once you are lighting light bulbs with the generator you will get a feeling for a reasonable speed of operation. (Again, it is easy to burn out bulbs with the generator. Try not to do so.)

Another student will connect light bulbs while the operator is turning the crank of the generator. Do not be afraid of the electricity generated. It is no more dangerous than flashlight batteries.

Begin without anything connected to the wires of the generator. Now connect one round bulb. The bulb should light without being too bright (the operator can adjust the speed of the crank to get a reasonable brightness). Connect and disconnect the bulb a couple of times. Ask the operator to describe how this feels.

While the operatorcontinues to turn the crank at this steady rate, light more round bulbs by adding them in parallel with the first one.Ask the operator to describe how this feels.

Take the time to rotate roles in the experiment now so that all students have the opportunity to be the operator and feel what happens as more bulbs are added.

What happens to the total amount of work that must be done by the generator operator as more bulbs are added in parallel? (It would also be correct to refer to the total amount of power that must be supplied.)

What happens to the total amount of light produced as more light bulbs are added in parallel? What do you suppose the addition of light does to the need for power?

Incandescent light bulbs get hot. What happens to the total amount of heat produced as more light bulbs are added in parallel? What do you suppose the additional heat does to the need for power?

As the generator operator works harder and harder, where doe this additional work go?

Now put down the generator and make a prediction: What would it feel like if you were turning the crank of the generator without anything connected to the wires and the two wires were then connected to each other? No light bulb would light. Would you be able to feel any difference? Make a prediction.

Now try it. Record your observations.

Based on your observations, is it easy to tell by looking at a device from the outside when it is consuming more or less power? Explain your answer.

If something is consuming (some might say “wasting”) power in a non-obvious way, where might that energy be going? Discuss your ideas with classmates and write down some ideas here. Then discuss your ideas with an instructor.

Full-circle: generator meets generator.

In the course of our experiments we have seen two devices that are sort of opposites but sort of the same:

The Flip-flap™ toy contains a “solar cell” or photovoltaic generator (“photo” means light and “voltaic” refers to electricity). The rectangular panel on the top of the Flip-flap is a generator which converts light to an electric “push” (or voltage) which pushes electric current through some wires to a small motor that makes the leaves move. The net result is that the Flip-flap converts light to electrical energy which is then converted to mechanical work (motion of the leaves).

When combined with the light bulbs, the Genecon becomes a device which converts mechanical work to electrical energy which is then converted to light.

What happens if we put them together???

You will need a Genecon, wires and a few light bulbs (long or round, it doesn’t matter), and a Flip-flap. Connect the bulbs in parallel in a way that will allow someone to hold them close to the photovoltaic cell on the Flip-flap. If possible, ask the instructor to dim the lights in the room for the maximum effect and of course an appropriate mood (isn’t this exciting?).

Have an operator turn the crank of the Genecon to get the light bulbs nice and bright. Have another team member hold the bulbs near the Flip-flap so that as much of the generated light as possible is reaching the photovoltaic cell. Crank away.

Record some observations.

Compare the amount of work that the Genecon operator seems to be doing with the amount of work that the flapping leaves on the Flip-flap are doing.

Would you say that all of the energy of the operator is being transferred to those leaves? Most of the energy?

Where might “missing energy” be going?

List some steps in this process where energy might be “lost.” (Note: Lost is not the same as destroyed. The energy is lost in the sense that it was misplaced. It went somewhere.)

Do you suppose that all of the work done by the operator went into electrical energy and all of that electrical energy went into light from the light bulbs and all of the energy in that light was picked up by the Flip-flap and all of the light that was picked up by the Flip-flap was converted to electrical energy and (gasp) all of that electrical energy was converted into the mechanical work done by the leaves?

(Yes, the answer to the last question was intended to be obvious. Careful reading of the last question should also suggest possible answers to the question before last.)

Scientists and engineers have done a great many experiments (literally millions) on all kinds of systems (mechanical, geological, biological, etc.) and the results are always the same. What we observed with the Genecon to light bulb to solar cell to Flip-flap experiment was not unusual. It is what always happens. Although our experiments have not demonstrated this conclusively, they have suggested two of the most important ideas in the science of energy.

Try to come up with two general statements about what happens in energy transformations:

When work is done, if one could look at the total amount of energy before and after an energy transformation (adding up all of the energy that goes into heat, sound, light, kinetic energy, potential energy, and anywhere else) what would be true about the total amount of energy before and after the transformation? This is a statement about the total amount of energy anywhere in the universe. Write out your answer in your own words.

If we specifically try to transform energy from one form into one specific other form (say heat into electrical energy or electrical energy into light), what does our Genecon to Flip-flap experiment suggest is true about the final amount of energy we will get in the form that we want? This is a statement about the efficiency of energy transformations. Write your answer in your own words.

Congratulations! You have just stumbled across the first and second laws of thermodynamics!