Abstract
Piezoelectric barbecue fire starters work by creating a spark that ignites the volatile lighter fluid, which then starts the charcoal burning. They are low current, high voltage devices. How high does the voltage have to get to make a spark in air? This project shows you a way to find out by with an inexpensive experimental setup to measure the distance that the spark can travel between two spherical electrodes.Objective
The goal of this project is to measure how many volts are produced by sparking barbecue fire starters. You can do this by measuring the distance the spark can travel. Two metal balls connected to the sparking element are used as electrodes for this experiment. How is the distance affected by objects in the spark gap?
Introduction
Air normally acts as a good insulator (or dielectric). However, when the voltage across an air gap becomes sufficiently high, electrons are stripped from the air molecules, ionizing the air and allowing current to flow. This is what is happening when lightning strikes during a thunderstorm. The process is called dielectric breakdown, and the voltage at which it occurs is the dielectric breakdown voltage.
The dielectric breakdown voltage for air is approximately 3000 V/mm (= 3 kV/mm), but also depends on other factors such as the geometry of the gap and the air pressure.
Piezoelectric barbecue fire starters work by creating a spark in air (see Figure 1, below).
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| Figure 1. Photo of a piezoelectric barbecue fire starter. When the button is pressed, a high voltage is generated between the positive electrode (red) and the ground electrode (six "fingers" surrounding the positive electrode), and a spark jumps across the gap. |
When the red button is pressed, a spring-loaded hammer inside the plastic handle hits a piezoelectric (quartz) crystal. Enough voltage is generated to produce a spark in air. The spark ignites the volatile lighter fluid and the resulting flames heat and ignite the charcoal.
In this project you'll learn how you can use two metal spheres (e.g., Baoding exercise balls, pinballs, or large ball bearings) with the barbecue fire starter in order to get a good estimate of the voltage produced by the piezoelectric mechanism. You'll connect the electrodes up to the metal spheres, and measure the distance that the spark can jump between them (see Figure 2, below). From the distance, you can calculate the approximate voltage between the two spheres. You can also investigate what happens when sheets of material (either conducting or insulating) are placed between the two spheres.
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| Figure 2. Measure the distance the spark can jump, both with and without sheets of material between the conducting spheres. |
Terms, Concepts and Questions to Start Background Research
To do this project, you should do research that enables you to understand the following terms and concepts:
Questions
Bibliography
Materials and Equipment
To do this experiment you will need the following materials and equipment:
Experimental Procedure
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Adult supervision is recommended for this project. The current produced by the spark is not dangerous, but it would certainly be uncomfortable if you were struck by a spark from the piezoelectric device. Observe the following safety precautions:
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| Figure 3. Barbecue sparker experimental apparatus. Fold the cardboard into a V-shaped groove, and tape the electrodes in place. |
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| Figure 4. Closeup of barbecue sparker experimental apparatus with a sheet of plastic between the conducting spheres. |
Variations
Credits
Written by Richard Blish, Ph.D. 
Edited by Andrew Olson, Ph.D., Science Buddies
Last edit date: 2006-06-09 21:30:00
If you like this project, you might enjoy exploring careers in Electricity & Electronics.
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