Fruit Salad De-Light

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Biology In Elementary Schools is a Saint Michael's College student project from a course that ran between 2007 and 2010 and fully described in this book chapter. The student-created resources have been preserved here for posterity. Link under 'toolbox' for printer-friendly versions of the exercises. Click on handouts to print full resolution versions. Please see Wikieducator's disclaimer, our safety statement, and the Creative Commons licensing in English and in legalese.

Student worthiness

tried and trusted

Primary biological content area covered

  • Electricity
  • Conduction
  • Insulation
  • Electrical Safety


  • 1 Multimeter
  • 4 Lemons
  • 2 Grapefruits
  • 2 Bananas
  • 1 Orange
  • Roll of Copper Wire
  • Large Metal Paper Clips
  • Pennies (dated before 1982)
  • 1 LED Light Bulb
  • 1 Incandescent Light Bulb
  • Knife
  • Wire Cutters


Figure 1: used to demonstrate the Scientific Method with this experiment

Figure 1: click to enlarge

Word Bank

Conductors- A substance or medium that conducts heat, light, sound, or especially an electric charge.

Insulators- a material that is a poor conductor (as of electricity or heat)

Current- a flow of electric charge

Battery - An energy storage device made up of one or more electrolyte cells.

Circuit(s) - A conductor or a system of conductors through which electric current flows. Electrical Energy - The energy associated with electric charges and their movements. Electricity - A form of energy characterized by the presence and motion of elementary charged particles generated by friction, induction, or chemical change. Electron - A subatomic particle with a negative electric charge. Electrons form part of an atom and move around its nucleus.

Volt (V) - The volt is the International System of Units (SI) measure of electric potential or electromotive force. A potential of one volt appears across a resistance of one ohm when a current of one ampere flows through that resistance. Reduced to SI base units, 1 V = 1 kg times m2 times s-3 times A-1 (kilogram meter squared per second cubed per ampere). [1]

Description of activity

The students will make a battery using fruit to produce enough electricity to light a small LED light.

Lesson plan


The lesson will begin with assessing the students’ knowledge of batteries by asking the following questions:

  1. Have you ever used a battery?
  2. Have you ever noticed the + or - signs on the battery?
  3. How does that affect the toy (for example remote controls)?

Then we will tell the students that we are going to be creating our own battery to make an LED bulb light up.

Gather materials and discuss with children whether or not they think that they will be able to get an LED bulb to light up or an incandescent bulb to light up with the above materials. Record their guess on the worksheet.

After they record their guess, tell them that it is possible (if they all think it’s not) and then have them guess how many pieces of fruit it will take to light up the LED bulb? Have them record the data. Ask if the students think that the fruit could light up an incandescent bulb? Have them record the data.


  • The students will begin by taking three pieces of copper wire with similar length (cut previously by the teacher to save time). The students will take the one piece of the copper wire and wrap an end of it around a paperclip. The students will take another piece of copper wire and wrap an end around one of the pennies. The students will take a third piece of copper wire and wrap one end around a penny and the other end around a paperclip(Figure 3).
  • Next, the students will take the lemons, grapefruits, and bananas, squeeze and roll them in order to loosen the pulp inside of the fruit (Do not push too hard. Pushing too hard will produce a hole in the skin of the fruits).
  • Once the fruits have been squeezed and rolled, the teacher will then cut two slits parallel to one another, one inch or so apart in the top of each fruit (Figure 4 & Figure 5).
  • The students will first begin with two lemons. They will put the first piece of copper wire into one of the slits in the first lemon, placing the paperclip end into the slit. The students will then take the second piece of copper wire and put it in the slit into the second lemon placing the end with the penny into the slit.
  • The third copper wire will be used to connect the first and second lemon together. The end of the wire with the penny on it will go into the first lemon and the end of the wire with the paperclip on it will be put in the slit in the second lemon. When the lemons are connected both lemons should have a penny and a paperclip, but they should NOT be touching (Figure 6).
  • The free ends of the wire are then connected to the multimeter (Figure 7). In order for the students to continue and try this experiment with the LED light, they will have to get a measure of 50 on the multimeter (Figure 8). If the students do not get this number they will have to add more fruit such as more lemons, grapefruits, bananas, or carrots. In order to do this they will have to create more copper wires (such as the third wire) which contains a penny and a paperclip.
  • The students will continue this process until they get 50 on the multimeter. When they do, they will disconnect the multimeter and then attach the LED light to the ends of the copper wires (Figure 9).
  • The light then should light up. (If the light does not light up then you may want to switch which wires are connected to which end of the light).

Step 3 - THE WRAP-UP

After lighting up the LED bulb have the following discussion with your students of why this experiment works.

  • Do you know what a conductor is?
    • Conductors are certain materials that allow electrons to flow through them.
  • We are working with two different metals (paper clip is zinc, penny is copper)
    • because they are two different metals the electrons are pushed around in a circle creating an electric current making it a circuit (A conductor or a system of conductors through which electric current flows).
  • The same metals will not work because the electric push would be equal (from each side – from the penny and penny or the paper clip to the paper clip) and electrons would not flow.
Energy Efficiency
  • Why is it that an LED bulb lights up but an incandescent bulb doesn’t???
    • because incandescent bulb require more voltage than this battery produces.
  • Why use Energy efficient light bulbs?
    • because they use less energy!

Potential pitfalls

What if the bulb doesn’t light? Try the following things:

  1. Make sure all pennies are from 1982 and before (after 1983 pennies are made primarily of zinc.)
  2. Make sure the two ends of the bulb are connected to the end of the copper wire.
  3. Make sure that the pennies and paper clips are placed inside of the fruit but try and keep the connected copper wire outside of the fruit.
  4. Make sure the bulb works.

Math connections

Students use math by recording data, using tables as well as forming a hypothesis on how much fruit will be need to light the LED using the worksheet (Fig 1).

Literature connections

  • Cole, Joanna, and Bruce Degen. The Magic School Bus and the Electric Field Trip. New York: Scholastic, Incorporated, 1997.

Connections to educational standards

  • 1.13 Students listen actively and respond to communications. This is evident when students: Ask clarifying questions; Restate; and Respond through discussion, writing, and using art forms.
  • 7.1 Students use scientific methods to describe, investigate, explain phenomena, and raise questions in order to: generate alternative explanations-hypotheses-based on observations and prior knowledge; design inquiry that allows these explanations to be tested; make and communicate conclusions, generating new questions raised by observations and readings.
  • 7.2 Students design and conduct a variety of their own investigations and projects; questions that can be studied using the resources available; data that are collected and recorded in ways that others can verify.
  • 7.11 Students analyze and understand living and non-living systems (e.g. biological, chemical, electrical, mechanical, and optical) as collections of interrelated parts and interconnected systems.

Next steps

There are many other activities that you can connect to this. Some being, units on electricity, energy conservation, metals, and maybe even a unit on composting!


Fruit Salad De-Light went off almost flawlessly. The lesson was exciting, engaging and informative. Both students and teachers alike thought the lesson was very “cool” and they couldn’t believe that with just fruit we were able to light up a small LED light. The students contributed to the discussion and all the students were able to successfully complete the worksheet. The students asked questions and made good predictions as to how much fruit it would take actually light up the LED bulb. It was interesting to us that each time we did the experiment we needed a different amount of fruit to make it light up. This could have been because of many different factors. When working with children there are more opportunities for small mistakes to get in the way of the scientific method. For example, one group may have pushed their copper wire in a little deeper than another group and that could have caused a slight difference. We also ran into a slight problem when one of our LED bulbs was out. We continued to add more and more fruit and rechecked every wire connection to no avail, eventually we decided to try another light and once we switched bulbs we had success! Overall, this lesson was very successful and I would certainly do it again with another group of students.

Citations and links