The Electrical Fruit Salad is a fun way to get to know how a multimeter works by making a battery out of your lunch items!
Multimeters are indispensable tools used on trades jobsites every day. From assessing the voltage level of batteries on a boat to checking for electrical continuity in a car wiring system, these tools are used to troubleshoot, diagnose, and test electrical systems in a multitude of settings. Getting familiar with how they work and what they can measure gives understanding to some of the many skills learned and used by tradespeople such as electricians and auto mechanics.
Teachers may also use this activity to experientially explore the science curriculum with students: Grade 4s learn about devices that convert energy (eg, a fruit battery converting chemical energy to electrical energy!), grade 5s learn about solutions and solubility (how the acid levels in the different foods conduct electricity to varying extents), grade 7s learn how electricity is generated and the environmental impacts of the different methods.
Multimeters are indispensable tools used on trades jobsites every day. From assessing the voltage level of batteries on a boat to checking for electrical continuity in a car wiring system, these tools are used to troubleshoot, diagnose, and test electrical systems in a multitude of settings. Getting familiar with how they work and what they can measure gives understanding to some of the many skills learned and used by tradespeople such as electricians and auto mechanics.
Teachers may also use this activity to experientially explore the science curriculum with students: Grade 4s learn about devices that convert energy (eg, a fruit battery converting chemical energy to electrical energy!), grade 5s learn about solutions and solubility (how the acid levels in the different foods conduct electricity to varying extents), grade 7s learn how electricity is generated and the environmental impacts of the different methods.
Tools & Materials
Material List
- Various fruits, vegetables, tubers, etc.
- five or more connector wires with alligator clip ends
- 2" pieces of thick copper wire (one per food item)
- galvanized (zinc) roofing nails (one per food item)
- one 3mm red LED bulb
Tool list
- multimeter
- damp cloth
- notebook
- pencil
- pliers or sidecutters to cut copper wire to length
Optional:
Procedure
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Choose which piece of food you want to make your battery out of. Insert your copper wire electrode and your galvanized zinc nail electrode, making sure they do not connect to one another inside the fruit.
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Clip one connector wire to the copper wire, and another connector wire to the nail.
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Set up your multimeter to read volts according to the instructions: plug the black cord into “COM”, and the red cord into “VΩ”. Set it to read “DC” volts at the largest number it can.
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Clip the free ends of the wires to your multimeter probe ends. If no numbers appear on the screen, switch the multimeter down to read smaller voltage amounts until you get numbers appearing (the “20” will usually work, if your multimeter has it). Your fruit is now a battery! -
In your notebook, write down the type of fruit you are testing, the settings on the multimeter that you are on, and the number of volts it reads. One at a time, try out all the different pieces of food you have collected! -
Try wiring up more than one piece of fruit in a row (this is called “in series”). Make sure that you attach copper anodes to zinc anodes (don’t attach copper to copper or zinc to zinc, as you want all the electron flow to go in the same direction). Record in your notebook the types of food connected and the voltage reading.
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Try connecting the LED into your circuit to see if you can make it light up! (Instead of clipping the connector wires to the multimeter probes, clip them to the LED wires instead). How many fruits in series does it need to power up? Note: LEDs need electricity to flow in one specific direction – each time you test the LED, test it in both orientations by reversing it and attaching the alligator clips to the opposite LED wires. -
Clean up by turning off the multimeter, disconnecting all the wires, then wiping down the alligator clips and table with a damp cloth. Remove the metal from the foods and save the nails and wire for another project. You can’t be sure that your wire and nails were food-safe and clean before starting, so compost your foods when you’re finished - do not eat them.
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If the copper wire is too thin to push into the food easily, poke a pilot hole with the nail first.
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If the multimeter is showing no voltage while your food is connected, try turning the multimeter dial to read a smaller voltage. You can also check that the multimeter is working by turning the dial to the continuity selection and connecting the probe tips together (if there are no numbers or no beep noise, your multimeter might need a new battery).
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If your LED won't light up, try reversing it as it will light up only when the electricity is flowing in one specific direction. Also, try adding additional fruits in series to up the voltage.
TROUBLESHOOTING
Extension Challenges
- When you connect foods together in series, do you notice a pattern in the voltage amount? Can you use this pattern to predict the voltage any two foods will produce when you connect them in series?
- Try wiring up different liquids with your copper and zinc electrodes by taping them to the inside of a small plastic cup, submerging the ends in the liquid. Can you make a battery out of a cup of vinegar? Fruit juice? Sea water?
- Explore using different metals other than copper and zinc. What other metals might turn the fruit into a battery? Do they produce the same amount of voltage in the same fruit as the copper and zinc electrodes do?