Making a battery
Grade level(s):Grade 4
Topic:Sources of electricity
A battery generates electricity by a chemical reaction.
Volt, Amp, voltmeter or multimeter, current, battery, copper, zinc, electrode, chemical reaction, charge, electron, potential.
What you need:
•Batteries (1 per pair of students)
•Battery holders (1 per pair of students)
•Lemons (1 per pair of students)
•Copper electrode (copper electrical wire cut 3-5cm long) (2 per pair of students)
•Zinc electrode (wood screw) (2 per pair of students)
•Wires with alligator connector clips (1 per pair of students)
•Voltmeters or multimeters (1 per pair of students)
•Notebook or scratch paper and science folder
•Transparency showing how a battery works
Pairs (preferable) or groups of four.
70 minutes total
15 min introduction, building batteries 35 min, discussion of activity and concepts 20 min
This is an inquiry-based activity in which students are given materials to make a battery. Students work in pairs and results are shared with the class. Content is discussed after the hands-on session.
Students sholuld know that electricity flows in a complete circuit, that electrons are charged particles, and that a difference in potential (separation of charged particles) is required for electrons to flow in a circuit. Students should also feel comfortable with using multimeters to measure electric current or potential.
1. Learn how a battery generates electricity through chemical energy
2. Students will understand that household batteries operate on the same principle and should be able to suggest other ways to make a battery.
3. Understand that a mechanical energy, light, and chemical energy can be converted into electricity
4. Understand that electricity is a form of energy that can be converted to other forms of energy, such as light and heat.
The power behind electricity comes from one of the smallest things known to science -- electrons. Electrons are tiny particles within atoms that have a minute electric charge. If a million million (1,000,000,000,000 -- write this number on the chalkboard or white board!) electrons were lined up, they would barely reach across the head of a pin. When electric current flows through a wire, these tiny particles actually surge through the metal of the wire -- just like water flows through a pipe. It takes an unbelievably large number of electrons flowing through a wire to light a bulb --approximately 6 million million million (6,000,000,000,000,000,000) electrons flow through the bulb each second (write this number on the board). The flow of electrons is called an electrical current and is measured in Amperes --- when 6 million million million electrons flow through an electrical circuit in one second, the current is approximately 1 Ampere (6,000,000,000,000,000,000 electrons = 1 Ampere).
Electricity is used for many important things in our lives: light, heat in our homes, computers, etc. In order for electrons to move (and for us to get electrical current to power our favorite devices), a source of energy is needed. This energy may exist in various forms: mechanical motion, light, heat, or a chemical reaction.
Chemical energy is the source of power in batteries. The simplest batteries consist of two different metals (electrodes) floating in a bath of acid. Atoms from one metal travel through the acid to the other metal releasing electrons. Eventually, when all the mobile atoms have been transferred, no additional electrons may be released, and the battery is dead.
Engineers make measurements when they are working with electricity. They measure voltage, current, resistance and power. By considering a simple circuit, a battery connected to a light bulb, one can see how engineers use these measurements:
In an analogy to water flow, a battery is like a paddle wheel that raises water up to a height --this is voltage.
As water flows through a pipe, electrons flow through the filament of the light bulb this is current.
As water flowing downhill through a pipe encounters friction, electrons flowing through the filament of the light bulb encounter friction and release energy -- this is electrical resistance.
The entire process converts electrical energy to light energy and heat energy.
Engineers abbreviate these electrical quantities as V (voltage), I (current), R (resistance). These are related to each other as follows: V = I x R. Electrical power (P) is related to voltage and current as follows:
P = I x V.
1) voltmeters should be reserved from SEP and students should be familiar with how to use them
2) copper and zinc should be obtained from a hardware store (thick copper wire stripped of insulation and zinc coated steel screws work well)
3) lemons or other fruit should be purchased close to the date of the investigation
Lesson Implementation / Outline
Pass out lab coats, greet class etc.
Recap of circuits lesson. Allow students to share experiences and insights from last week, if appropriate. Key concepts: Electricity requires a complete path of conductive material such as metal in oder to flow. This path is called a circuit. The flow of electricity in the circuit is called current. A circuit containing one path and multiple items (such as light bulbs) in a row is called a series circuit. A circuit with two or more paths for the current to take is called a parallel circuit.
Introduction to energy and electricity as a form of energy. Discuss worksheet the students did about power plants. How did the power plant generate electricity? Somehow, some form of energy was used to generate electicity. Electricity is another form of energy that can be converted into other forms of energy that are useful to people, such as light or mechanical energy. Introduce students to first activity, in which they will experiment with electicity generation from mechanical energy and from sunlight.
Students are given materials and a worksheet and asked to see if they can make the needle on the voltmeter move. If they succeed, ask them if they can make it move further. If they succeed, ask them if they can light up a lightbulb.
Show the students a typical alkaline battery. Ask them how it works.
Explain that, within a battery, a chemical reaction takes place between an electrolyte and electrodes. An electrolyte can be a liquid acid or a dry chemical. The electrodes are two different conducting materials, such as metals.
Batteries come in two categories: dry cell and wet cell. Dry cells (such as flashlight batteries) are the alkaline batteries that use a powder chemical for an electrolyte; wet cells (such as car batteries) use acids as the electrolyte. The
students will create a wet cell battery using the juice of a lemon, which is a mild acid, as the electrolyte.
• The voltage (V) and current (I) delivered by the lemon battery will be measured using a voltmeter. Show the voltmeter. Give a very brief introduction to the voltmeter and tell students it will work best when set to 2.5V.
• Divide the class into pairs. Give each pair a D-size battery, a lemon, a copper electrode (zinc screw) and a zinc electrode (copper wire).
Building the lemon battery:
• Direct each pair of students to first press down on the lemon and roll it on the table to get the juices flowing inside.
• Have the students insert the zinc screw into the lemon so that approximately half of it is still protruding out. About 2 cm away from the screw insert the piece of copper wire into the lemon. These are called the electrodes of our cell. Be sure that the electrodes not touch each other on the inside of the lemon.
Go around to each group with voltmeter ready to read DC voltage on the lowest setting (2.5V), read the voltage of the battery. Hold the display or needle of the multimeter so that everyone can see and read the umbers. The battery votage should ready approx. 1.5Volts. (show that this is wrtten on the side of the battery, confirming in the students' minds that the multimeter works properly) If the reading is less than 1.5V, the battery is probably old and has lost some of its energy.
Now use the voltmeter to read the voltage across the electrodes of the lemon battery. The multimeter should read approximately I volt. Digital LCD displays might sh0.997 Volts or 0.989 Volts.
After taking readings from each pair look at the results by averaging the readings for all paris in the classroom.
Have students try to light an LED light bulb:
Background: Electrical power is the harnessing of electrons in motion. In the lemon cell the copper electrdoe is giving off electrons to the zinc coated screw. (making the positive electrode the copper, and the negative electrode the nail). The citric acid in the lemon acts as our electrolyte, which is what allows the electrons to flow from one electrode to the other.
If you attach a wire between the 2 electrodes you are creating a loop for the electrons to flow in and this quickly wears out the cell (called a short circuit).
If you attach instead a "load" to harness the energy to do something useful, like a LED light bulb, you can convert the elctrical energy into light energy.
Let's do this: to attach the LED, find the flat side of it and attach the negative lead (the alligator clip and wire which is red) to that side, this will be attached to the zinc screw. On the other side attach the positive lead (the alligator clip and wire that is black) to the copper wire. Low attach the negative lead to the zinc screw and the positive lead to the copper wire, check to see if the LED lights up. It will not because there is not enough power with just 1 lemon to do the work. Let's add another lemon cell (with the same wire set up). To attach two lemons together to increase the voltage so you can light the bulb, attach the positive lead of one lemon to the negative lead of the next. Now you have two times the voltage as with one cell, so the LED should dimly light up. If you add 3 lemons the light will shine more brightly and when there is a groups of cells working together this creates a battery.
Explain how it takes 100 watts to power a 100 watt light bulb, the more the wattage, the greater the power consumption. Tell the students that 1 million lemon batteries would be required to power a 100 watt light bulb.
An electric car requires 6000 W of power to run. Tell the students how many lemon batteries would be required to power an electric car. [Answer: 60 million (60,000,000 lemon batteries, employing 60 million lemons!]
Let, them think about that for a minute.
Does it make sense to use lemons to power a car. What are some of the pros and cons?
Pros - does not pollute, renewable energy source, electric cars are quiet etc.
Cons - cannot recharge lemons, they are heaby, expensive 25cents per lemon = $15million
Explain that the point was to explain the principles of batteries and electricity; that a simple lemon could be made into a battery by creating a chemical reaction.
Student understanding will be assessed after the wrap-up or by written reflection.
List observations from the class about that worked and what didn’t. Come up with a general observation together.
Electricity is the flow of charged particles. All matter is made up of atoms, and all atoms contain charged particles. There are different types of atoms. Some types of atoms tend like to get rid of negatively charged particles and some atoms like to accept them. The negatively charged particles are called electrons. When these two types of atoms are put next to each other, eletrons flow from one atom to another. This flow of particles is electricity and is the basis of a battery.
Many batteries consist of a zinc electrode in an acid solution. Zinc donates electrons in the presence of acid, which conducts electricity. Since electrons repel each other and are attracted to positive charge, they travel to the anode and go around the circuit to get back to the zinc electrode. Give teaser for next lesson, when they will use electricity to make a magnet and learn about motors.
Extensions and Reflections
This is a great opportunity to talk about electricity as a form of energy and its conversion into heat, light and motion, and vice versa. Also, it's a good time to discuss how a power plant works and perhaps organize a field trip to a wind farm, solar energy farm, or power plant. Solar panels make very exciting demos and are avaiable at SEP. Also, consider helping make your school a solar school.
This is a tricky investigation, and students may experience frustration. Guide them to success by pointing out the things that are logistically wrong (circuit not complete, voltmeter not on right setting) as you pass through the class if they get frustrated.