Type (Physical Science, Earth Science, Life Science, Social Science, Mathematics and Computer Science, Engineering, Other)
Physical Science
Grade Level (Elementary, Middle, High School)
Upper Elementary (Grade 5) and Middle School (Grades 6-8)
Difficulty of Project (Easy, Medium, Hard)
This project is fairly easy and inexpensive to perform.
Cost
$25.00
Safety Issues
The fruits used in this project should not be eaten. Care should be taken when handling the metal electrodes, LED and alligator clip leads.
Material Availability
Various fruits varieties, multi-meter, LED, alligator clip leads, and Tri-fold cardboard display board, all can be purchased locally. The copper and zinc electrodes can be ordered online.
Approximate Time Required to Complete the Project (Hours, Days, Weeks)
One day after of the materials are secured.
Objective
What is the project about?
The research aspect of this science fair project is to construct batteries (wets cells) made from various fruits and tests them to see which one will produced the most electric current.
What are the goals?
To create a battery from common fruits that when connected in a circuit will produce enough electricity sufficient to light an LED, or small hobby motor. To determine the amount of electricity produced a multi-meter will be used which will display both the voltage and current. Several fruits following a consistent testing procedure will be used and the results displayed in a data table, graph, and other visual aids.
In conducting this project the young investigator will apply the knowledge gained form this study to determine if it would be practical to use fruit as a natural source for generating electricity.
Materials and Equipment / Ingredients
What materials are required?
Alligator clips, lemon, grapefruit, orange, tomato, Kiwi fruit, copper and zinc metal electrodes, multi-meter capable of measuring small currents, RadioShack,# 276-330 LED, and an optional small 1.5 volt electric hobby motor.
Where can the materials be found?
The various fruits used in this project can be purchased from the local supermarket. Copper and zinc metal strips can be ordered online from Indigo Instruments.
The multi-meter (an electronic instrument used to measure the electric current in a circuit), can be found at the local home supply outlet (Lowes or HomeDepo), from a RadioShack retailer, or the local electronic repair store.
Alligator clips, LED, and the optional hobby motor, are available at the local RadioShack retailer or online at www.radioshack.com. Also, a Tri-fold cardboard display board can be purchased from an art & crafts supply store.
Introduction
Background information
An electric current is a flow of electrons (analogues to a flow of water) and is measured in units called amperes or "amps." Voltage is the force that pushes the electrons through a circuit (analogues to the pressure on water in a pipe) and is measured in volts.
When two dissimilar metals are placed in a common conducting solution (electrolyte) electricity will be produced this is the basis of the electro-chemical cell or wet cell. In the early nineteenth-century Alessandro Volta used this fact of physics to invent the voltaic pile and discovered the first practical method of generating electricity. Constructed of alternating discs of zinc and copper metals with pieces of cardboard soaked in a salt solution between the metals, his voltaic pile produced an electrical current. Alessandro Volta's voltaic pile was the first "wet cell battery" that produced electricity.
A wet cell consists of a negative electrode; a positive electrode and an electrolyte, which conducts ions (atoms with an electric charge). In this science fair project copper and zinc metals will be used as the electrodes and the citric acid found in fresh fruit is the electrolyte. The chemistry behind the fruit cell is that zinc is more reactive than copper which means zinc loses electrons more easily than copper. As a result, oxidation occurs at the zinc metal strip and zinc metal loses electrons to become zinc ions. The electrons then flow from the zinc strip to the copper strip through an external circuit. At the copper strip, reduction occurs the hydrogen ions in the fruit's critic acid juice accept these electrons to form hydrogen gas; this explains why the investigator may observe bubbling of gas produced at the copper strip when the two metals are connected by a wire.
In this project an LED is used to indicate if the fruit-cell is generating an electric current. A Light Emitting Diode (LED) is a semiconductor device which converts electricity into light. An electric current can flow only in one direction through LEDs which means that they have a positive and negative terminal, also referred to as the anode and cathode. The cathode should be connected the negative zinc metal strip, and the anode to the positive copper strip. LEDs have their cathode and anode marked in some manner usually the anode wire is often the longer of the two leads.
Diagrams and Pictures
The following sites offer down loadable images of fruit battery-cells that can be used on the display board:
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