Science Bug Experiments

Catch the Science Bug Kit Parts:

3 volt coin battery

3 clear LEDs

1 220 ohm resistor

1 1K ohm resistor.2 strips aluminum foil

1 strip electrical tape

1 science bug cutout

1 piece of boondoggle

1 Science Bug booklet

What is Electricity?

Everything in this world is made of atoms. Atoms are tiny balls that are made of three kinds of tiny particles: electrons, protons and neutrons. Electrons have a negative charge, almost no mass and are moving around the outside part of the atom in paths called shells at the speed of light. Sometimes the outside electrons can be pushed so that they jump from one atom to another atom. Electricity is the flow of electrons from one atom to another.

Atoms or molecules that are pretty easy going about accepting or giving up an electron are called “metals” and conduct electricity. Atoms that have a hard time passing an electron to another atom are called insulators. If pushed hard enough, electrons can be pushed from any atom. This is what happens with lightning, which pushes the electrons so hard, that even though air is a very good conductor, the electrons still jump from atom to atom..

The Properties of Electricity

There are three different properties of electricity that you will want to know in order to understand electronic circuits:

Voltage - How hard the electrons are being pushed. This is also called the “electromotive force” and is measured in Volts.

Current - How many electrons are passing a specific point in the circuit at a given time. Current is measured in a unit called amperes which is typically abbreviated to just “amps.”

Resistance - How much the properties of the wire and other electrical components limit the flow of electrons through the circuit. Resistance is measured in Ohms.

What is a Circuit?

In order to do something useful, there must be a complete path for the electrons to move through. If this path isn’t a complete circle, the electrons will not flow. A path for electrons to flow through that causes them to do useful work is called a circuit. If there is a shortcut in this path that lets them complete the circle without doing the work, then the electrons won’t do the work, and this is called a “short circuit.”

Resistor Color Code

The amount of resistance a particular resistor has is encoded using the “Resistor Color Code” as colored bands on the resistor. The first two bands represent the first two significant digits of the resistance, the third band is how many zeros there are. The fourth band is the tolerance. In writing resistance the letter “K” is used to represent 3 zeros, and “M” to represent 6.

Light Emitting Diodes

A light emitting diode is an electrical component that can emit light. Electrons orbit around an atom in “shells”. The further out from the center of the atom an electron is, the higher its potential energy, similar to the further something is from the ground, the further it can fall. When atoms of two different types are placed together and electricity is passed through them, the electrons have to move to a different shell. If the electrons move from a high energy shell to a low energy shell, they lose some of this potential energy. If this is the right amount, this energy becomes light. Depending on the amount of energy (which depends on the difference in the outer electrons shells of the two atoms), different colors of light will be emitted. Red, and yellow light will require the least amount of drop in shell, and have the lowest energy, blue and violet will have the biggest drop, and take the most energy. If you connect up the LED in the opposite direction, current won’t flow (because the electrons have to go “uphill” absorbing energy. Because of this LEDs will only work in one direction in a circuit.

Polarity

Sometimes it matters how to connect an electrical component up to a circuit, and sometimes it doesn’t. If it matters, a component is said to have “polarity.”

Component Polarity

Resistor None

LED Yes, + side is the longer lead.

Battery Yes, + side is inscribed on the battery

Reading a Schematic

When we write we draw symbols that represent the letters that make up the words. Electrical engineers use symbols to represent different electrical components, and create drawing that show how each electrical component is connected together. These drawing are called “schematics.”

Experiment 1: Lighting a Single LED

Place the battery between the two leads of a LED so the longer lead (positive) is touching the positive side of the battery (it should have a + symbol on the battery) and the shorter lead (negative) is touching the other side of the battery. The LED should light up. Try this again with the other LEDs in your kit.

Questions:

Why does the LED only light up when both sides are touching the battery?

Because it needs to complete the circuit. Unless the battery is touching both sides of the battery there isn't a complete circuit and the electricity will not flow.

Why does it matter which side of the LED is connected to positive and which side is connected to negative on the battery?

An LED emits light when the electrons fall from an electron shell of a higher energy level to an electron shell of a lower energy level. If the LED is connected to a circuit the wrong way, the electrons won't flow at all, (because it is "uphill") or if they are pushed hard enough so that they will flow, they will still be going "uphill" from a lower energy shell, to a higher energy shell, and so no light will be created.

Which LED when connected by itself is the brightest?

This should be the red LED. This LED has the lowest voltage drop, because red light has the lowest amount of energy. Because this drops the lowest amount of voltage, the circuit through this LED will have the highest current, and will emit the brightest light. It may be difficult to see which LED is the brightest, because our eyes don't perceive all colors with the same brightness at the same level.

What causes the LEDs to have different colors?

The various LEDs are made with different atoms. These atoms have different electron shells, with different energy levels. The color of light that is created is based on the difference in the energy shells of the electrons of the two different types of atoms used in the LEDs. By choosing different types of atoms, the light created has different wavelengths which are perceived by us as different colors.

Experiment 2: Lighting More Than One LED

While one LED is connected to the battery, try to connect another LED so that it lights up at the same time.

Questions:

Are you able to light up more than one LED at the same time?

Yes, you should be able to light up two LEDs (as long as one of them isn't Red or Orange).

Can you light up all three LEDs?

No, not by hooking them up straight like this. The Red or Orange LED will draw too much current, which will lower the voltage of the battery to the point where the green or blue LED don't light up at all.

Does the color of the LEDs matter when you are trying to connect up more than one LED?

Yes, Red and Orange LEDs will draw the most power and have the smallest voltage drop, so when they are being lit, the other LEDs won't light up.

What happens to the brightness of the first LED when you connect up the second LED to the battery? Why?

The first LED gets dimmer. This is because the electrons are flowing through two LEDs now, and so not as many of them are flowing through each LED. The amount of light is determined by the amount of electrons flowing (the "current") and so the LEDs get dimmer when more than one of them is connected.

Why do the red or orange LEDs not light up at the same time as the other colors?

Red and Orange light, have the longest wavelengths, and the lowest amount of energy. Because of this, the voltage drops the least when it goes through these LEDs. This means that there is is a greater electromotive force pushing the electrons through the circuit when these colored LEDs are used, and so the electrons won't flow through the other colored LEDs (or if they do because you have a very fresh battery, it won't be enough to light the other LEDs enough so that you can see it).

Experiment 3: Making a Switch

Place the battery with the positive side up on top of a strip of aluminum foil. Hold the LED so that its shorter lead (negative) is touching the foil, and its longer lead is just above the positive side of the battery. To turn on the LED with your other hand lightly press on the lead that it is above the battery.

Questions:

Why does having the LED touch the foil work as well as having the leads on both sides of the battery?

The atoms in the aluminum foils are "metals" which means that electrons flow easily between atoms. This makes aluminum a conductor, and so connecting the LED up straight to the battery should work as well as when it is connected through the foil. Switches in electronics are made this same way, by placing a conductive substance in such a way that it mechanically makes or breaks the circuit. If you are careful, you might be able to make your own switch from the two strips of foil with each side connecting to one side of the LED. Make sure that you don't let the two pieces of foil touch, or there will be a short circuit, and the LED won't light up at all.

What properties do the aluminum atoms of the foil have that make it so it can conduct electricity?

The outer shell of electrons in the aluminum atoms are easily passed to other atoms. This is because the atomic number for aluminum is about half way between the atomic numbers of two noble gas elements, and so the shell is about half full, making the aluminum atoms equally willing to accept new electrons as they are to release electrons to another atom.

Experiment 4: Connecting Through a Resistor

Bend the longer lead of a LED so that it is about 90 degrees to the other lead. Twist one side of the 220 ohm (Red, Red, Brown, Gold) resistor around this lead. Touch the other side of this resistor to the positive side of the battery and the short lead of the LED to the negative side of the battery. The LED should again light up. Try this with another LED and the 1K ohm resistor (Brown, Black, Red, Gold).

Questions:

Is the LED as bright as it was without the resistor? Why not?

No, the LED isn't as bright when the electricity also has to flow through the resistor, because the resistor is limiting the amount of electrons that flow (the "current") and thus the amount of light that is produced by the LEDs.

Why does which resistor you use with an LED change how bright the LED is?

The two resistors have different amounts of resistance. The 1K resistor is roughly 4x the resistance, and so when it is connected up in a circuit, the LED is only about 1/4 as bright as when the LED is connected to the 200 ohm resistor. Electrical engineers will carefully which resistors they use so that the right amount of current flows through each electrical component.

Why would using a resistor make the battery last a longer amount of time?

By limiting how much current flows through a circuit, a resistor will limit how quickly the battery is depleted. A higher value resistor will cause the LED to not be as bright, but it will also help the battery to last a lot longer, because less electrons are flowing.

Experiment 5: Two LEDs Through a Single Resistor

Place two of the LEDs (don’t use the yellow or red LED) next to each other and bend their longer lead (positive) sides up so they are parallel to each other and touching, while positioning the negative leads so that they are also parallel and touching. Twist the 220 ohm (Red, Red, Brown, Gold) resistor around both of the positive pins. Touch the other side of this resistor to the positive side of the battery while holding both of the shorter leads from LEDs on the negative side of the battery. Both LEDs should light up.

Questions:

Are the LEDs as bright as they were when just one was connected to the resistor? Why not?

No, because the electrons now have two paths to take through the circuit, and so the number of electrons is shared between the two LEDs. If you use the orange or red LED, the majority of the electrons will flow through this LED and the other LED may not light up at all.

Experiment 6: Parallel Resistors

Place the two resistors so that their leads are parallel to each other, and then twist one lead of each together, and then twist the leads from the other side together. Then using this “parallel” resistor made up of two resistors, connect up an LED to the battery as you did in the previous step.

Questions:

Is the LED that you connect up this way, brighter than when you just used one resistor? Why?

Yes. Connecting both LEDs like this in parallel, gives the electrons two different paths to flow through, and so it decreases the amount of resistance. This is similar to saying you can blow more air through two straws than you can blow through just one straw (as any school kid who has ever blown bubbles in their milk knows :) ). If you hook up two resistors in parallel that have the same resistance, this will half the total amount of resistance. In our case connecting a 220 ohm resistor in parallel with a 1K resistor decreases the total resistance to 180.33 ohms.

Experiment 7: Three LEDs Lit at the Same Time

Using what you’ve learned from the previous experiments, you should be able to find a configuration with the battery where all three of the LEDs are lit with the battery at the same time.

Question:

Why did you need to include a resistor in order to get this to work?

The resistor on the red or orange LED prevents it from drawing too much current. This causes more electrons to flow through the other LEDs so that they can light up as well.

With a friend who has an additional kit, try the following two experiments...

Experiment 8: Series Batteries and LEDs

Hold the two batteries so that the positive side of one battery is touching the negative side of the other battery. Now connect up a LED to a resistor, like you did in experiment #4, except have the resistor touch the positive side of one of the batteries, and the negative lead of the LED touch the negative side of the other battery.

Questions for experiment #8:

Why is the LED brighter than it was with just one battery when you did experiment #5?

Connecting batteries in this way adds their voltages together. This means that instead of just 3 volts of "push" (electromotive force) on the electrons there is 6 volts of "push." More volts ("push"), means more electrons flow, and more electrons flowing means more light is created by the LED.

Why is it important that you not try this experiment without the resistor?

Too much current could flow through the LED which might burn it out. (It would get hot, and the atoms in the LED would melt apart to the point that it wouldn't work any more.

What happens if you place a piece of paper between the two batteries, does the LED stay lit? No, because the paper doesn't conduct electricity (it is an "insulator), and there has to be a full circuit for the LED to light up. Placing a paper between the two batteries breaks the circuit.

What happens if the two batteries are separated? Why doesn’t the LED stay lit?

This would also break the circuit, and so the electricity wouldn't flow. In order for the batteries to push electrons through the circuit both ends of the batter need to be connected.

If you flipped one of the batteries, so that both their positive or both their negative ends were touching, and then connected the LED to both outside ends, would it stay lit?

No. Although this would be a complete circuit, connecting the batteries in this would would have the voltage of one of them cancel out the voltage of the other. Because there would be no voltage difference between the two sides of the LED, no current would be forced to flow through it, and so the LED wouldn't light up.

Experiment 9: Parallel Batteries:

Place two batteries on one piece of aluminum foil so that they two negative sides are connected through the foil. Place another piece of foil on their top sides so that the two positive sides are connected through the foil. (Make sure you don’t let the two pieces of foil touch the other foil or one of the other sides). Now connect up LEDs like you did in experiment #2. The LEDs should light up.

Questions:

Are the LEDs brighter than they were with just one battery? Why not?

Not with just one LED, because connecting the batteries in this way wouldn't increase the voltage, and so the current flowing through the LED would stay about the same. This would increase how many LEDs could be connected up to the batteries, however', because having batteries connected in parallel like this increases the amount of current that they can supply.

Can you connect more LEDs and have them still stay lit, than you did with just one battery? Why?

Yes, batteries connected like this help each other add to the current available, and so can light up more LEDs than just a single battery.

If you had only one LED hooked up to these two batteries in this way, would it last longer than the LED hooked up to two batteries in series (experiment #8?)

Only one LED hooked up to both of these batteries would last a lot longer, because the current would be evenly shared between the two batteries and so the LED would last about twice as long. (This wouldn't be exact because no two batteries have exactly the same amount of charge).

Experiment 10: Science Bug:

Find two LEDs that will light up when placed on the battery. With the electrical tape secure them in place, and then tape the LEDs and battery to the science bug cutout, so that your science bug has two glowing antennas. Fasten the science bug to the boondoggle and tie an overhand knot in the boondoggle using both ends so that it forms a necklace. Wear your science bug necklace with pride and show others that you’ve caught the science bug!

More Information

For answers to the questions, demo videos on how to do the experiments, and information and links to more experiments that you can do with your club, go to: http://tiny.cc/sciencebug

Let Jessica help you spark the 4-H science bug in your club!

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