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Avoid the Shock of Shocks! Build Your Own Super-sensitive Electric Field Detector

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Wouldn't it be nice to avoid those nasty electric shocks you get after you have walked around on carpet and then touch a doorknob? These shocks are caused by static electricity. In this project, you will build a super-sensitive charge detector to investigate the electric fields created by static electricity. The detector can sense invisible electric fields before you touch something and get zapped, so try this project to avoid the shock of shocks!


Areas of Science
Time Required
Very Short (≤ 1 day)
Familiarity with using a solderless breadboard, or willingness to learn.
Material Availability
A kit is available from our partner Home Science Tools. See the Materials section for details.
Average ($50 - $100)
No issues

David Whyte, PhD, and Ben Finio, PhD, Science Buddies

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Build a sensitive electric field detector and use it to measure how well different materials hold electric charge.


Static electricity is the accumulation of electrical charges on a surface, produced by the contact and separation of dissimilar materials. If you have ever received a shock when touching a doorknob, you have some firsthand experience with static electricity. The sparks created by static electricity can cause real problems, such as when they "fry" an electronic component in a computer.

Objects are usually electrically neutral, meaning they have an equal number of positive and negative charges. When two different materials are rubbed against each other, one of the materials often donates electrons to the other one. Electrons are elementary particles that carry a negative charge. If an item gives up electrons to another item, the first item will end up with a net positive charge. On the other hand, the item that now has extra electrons will have a net negative charge. Items that have a net negative or positive charge are surrounded by an invisible electric field, which attracts opposite charges and repels similar charges.

The materials listed below are ranked in order of their ability to hold or give up electrons. This ranking is called the triboelectric series. If two materials are rubbed together, the one higher on the list will donate electrons and become positively charged.

Triboelectric Series

For this project, you will build a simple, but extremely sensitive, charge detector. When it is assembled, it will be able to sense the changes in the static electricity on your body as you walk over carpet, when you pet your cat or dog, or when you touch a plastic pen or brush to your hair. Figure 1 shows a circuit diagram for the charge detector. Circuit diagrams are schematics that electrical engineers use to represent circuits. Each symbol represents a different electronic component. However, do not worry if you do not understand the circuit diagram. The procedure of this project will provide step-by-step instructions for how to build the circuit on a breadboard.

Circuit diagram for a solid-state charge detector
Figure 1. This is a circuit diagram for a solid-state charge detector. It can detect very weak electric fields.

As shown in Figure 1, the circuit has three components: a 9 V battery, a light-emitting diode (LED), and a field-effect transistor (FET). The field-effect transistor has three leads: a source (S), a gate (G), and a drain (D). A thorough description of how the field-effect transistor works would require delving into advanced electrical engineering, but the essential features can be seen in Figure 2. In semiconductors, electrons and "holes" act as charge carriers. The more-abundant charge carriers are called majority carriers. In N-type semiconductors they are electrons, whereas in P-type semiconductors they are holes. The field-effect transistor has a channel of N-type semiconducting material that allows electrons to carry a current. When the battery is connected to the transistor, a voltage is applied across this N-type semiconducting material.

Field-effect transistors are normally on devices, meaning that with no negative electric field, they allow maximum current to flow. In the middle of the N-channel is a region of P-type semiconductor. Around the P-type material, there is a depletion zone. There are fewer electrons in the depletion zone, so the bigger the depletion zone is, the higher the resistance. In the presence of a negative electric field, the depletion zone gets bigger, the current is decreased, and so the LED on the circuit is turned off.

The field-effect transistor circuit can be compared to a water faucet. In this analogy, the voltage is like the water pressure, and the field-effect transistor is like a faucet. When you open a faucet, water flows because of water pressure. The water will keep flowing until the faucet is closed. In the circuit, electrons flow through the FET and LED. The electrons flow because of the voltage supplied by the battery. Because electrons are flowing through the LED, it glows red. When the FET is "closed"—by bringing an object with a negative charge near the gate pin—electrons cannot flow through the circuit, and the LED light dims.

Simplified diagram of an outside magnetic field closing the inner gate of a junction field-effect transistor
Figure 2. Schematic of an N-channel junction field-effect transistor (JFET, a sub-type of FET). It is made from a single piece of N-type semiconductor, constricted in the middle by P-type material forming the gate. Varying the gate voltage modulates the current flow through the device. When the gate voltage is made more negative, it constricts the current path in the region of the gate, increasing its resistance and reducing the current flow.

Terms and Concepts

Before you begin this science fair project, you should be familiar with these concepts:



This website is the source for the circuit used in this project. The website also has some entertaining variations of the basic project.

Check out these websites for additional information.

Materials and Equipment Buy Kit

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Experimental Procedure

Notes before beginning:
  • Be very careful when assembling this circuit. It is possible to burn out the LED or the transistor by incorrectly connecting them to the 9 V battery. Make sure you carefully count the rows of the breadboard when you assemble your circuit.
  • Try to avoid touching the transistor's leads directly, especially the gate lead. Handle the transistor by the plastic packaging when you pick it up. A large static discharge can damage the transistor

Assembling Your Charge Detector Circuit

Important: your Sensor Kit contains two parts that look very similar: a transistor and a Hall effect sensor. They are both small black plastic parts with three metal legs. This project requires the transistor. When viewed from the top, it is bigger than the Hall effect sensor and rounded on one side, as shown in Figure 3. Make sure you use the transistor, or your circuit will not work!

Top-down view of a hall effect sensor and transistor inserted into a breadboard
Figure 3. Hall effect sensor (left) and transistor (right) viewed from the top.

Assemble your charge detector circuit on a breadboard, as shown in the slideshow and described in Table 1. If this is your first time using a breadboard, refer to the Science Buddies resource How to Use a Breadboard for Electronics and Circuits. For a circuit schematic, see the Help section.

Slideshow with step-by-step instructions viewable online.

Part Picture Breadboard Symbol Location
A MPF102 JFET transistor
Breadboard diagram symbol for a MPF102 JFET transistor
A1, A2, A3. Writing must face to the right.
A red LED
Breadboard diagram symbol for a red LED
Long lead in B3
Short lead in B4
100 kΩ resistor
A 100000 ohm resistor
Breadboard diagram symbol for a 100000 ohm resistor
One lead in C1
9 V battery and snap connector
A 9 volt battery
Breadboard diagram symbol for a 9 volt battery
Red lead to E2
Black lead to E4
Table 1. List of circuit components and their locations. Source material for breadboard symbol images credit Fritzing.org.

Measuring Electric Fields

  1. Learn how to use your charge detector. Once you have finished assembling it, the LED should be on (see Figure 4). Try rubbing different objects from the triboelectric series against each other and bringing them near the "antenna" (the free lead of the 100 kΩ resistor). What happens? Here are some tips for using the circuit:
    1. When you rub two objects together, the one lower on the triboelectric series (meaning it has a negative charge) should cause the LED to go out when you bring it near the circuit. The object higher on the series (with a positive charge) may cause the LED to get slightly brighter, but this can be difficult to see since the LED is already on. This project works best if you bring negatively charged objects near the circuit.
    2. The charge on an object will dissipate if you handle it, especially if your hands are slightly damp. By handling the object, the charged particles are transferred from the object to your skin. You can keep the charge from being lost by isolating the charged object; for example, by quickly placing it on an insulating surface (like a wooden tabletop) next to the circuit, or by suspending the object with string made out of nylon, or some other insulating material.
    3. The LED might turn off completely after the circuit is exposed to a strong positive field. You can "reset" the circuit by tapping the resistor leads with your finger, or by waving a negatively charged object (such as a plastic pen that has been run through your hair) near the antenna.
    4. See the FAQ if you have trouble with your circuit.
Completed breadboard circuit for an electric field detector
 An electric field detector circuit on a breadboard next to a plastic cup
Figure 4. Top: the LED is on when no objects are near the antenna. Bottom: the LED turns off when a negatively-charged object (in this case, a plastic cup that was just rubbed against human hair) is brought near the antenna.
  1. Select one material from the positive end of the triboelectric series (human hair works well) and an assortment of materials in the neutral and negative parts of the series. You will rub all the other materials against the first one.
  2. If possible, prepare all your materials in one place, on a single work surface, so you can do the experiment without walking around. Moving around (especially on carpet) can cause static electricity to build up on your body, and this can affect your results.
  3. Rub two materials together and immediately place the negatively charged one directly next to the antenna. Use a stopwatch to time how long it takes the LED to come back on. Repeat this for each of your materials (make sure you rub each material the same number of times), and do at least three trials for each material.
  4. Set up a ruler to measure the distance from the antenna. Rub two materials together and then slowly move the negatively charged one toward the antenna until the LED goes out. Record the distance at which the LED goes out. Again, repeat this for each of your other materials and do at least three trials. Remember that the objects might lose charge as you hold them, so you might need to devise a technique to move the objects closer to the antenna without touching them. For example, you could slide them on a wooden block or suspend them from a string.
  5. Analyze your data. Which material holds its charge the longest? Which one generates the strongest electric field? If you rank the materials for each category, is the order the same? Are your results consistent with what you would expect based on the triboelectric series?
  6. There are many other things you can do with this circuit. See the Variations section of this project and the Experiments section of this page for more ideas.


For troubleshooting tips, please read our FAQ: Avoid the Shock of Shocks! Build Your Own Super-sensitive Electric Field Detector.

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Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.


  • Try using different lengths of wire as an antenna for your circuit. Your kit comes with several short jumper wires and much longer alligator clips, which you could also use. Does a longer antenna increase the circuit's sensitivity?
  • Keep track of the humidity and record how it affects your static electricity experiments.
  • Build a permanent version of the circuit using solder to make the connections.
  • Charge an object, for example, by running a pen through your hair. Now support the pen with different materials and place it near the antenna to see which is best at keeping the object charged.
  • Can you detect electric fields that are created when you pet your cat or dog?
  • Charge an object, hold it near the antenna to dim the LED light, and then pass other objects between the object and the antenna. What happens?
  • Does changing the number of times you rub an object back and forth to charge it affect either how long it will stay charged or the distance at which you can detect its electric field? Why or why not?

Frequently Asked Questions (FAQ)

If you are having trouble with this project, please read the FAQ below. You may find the answer to your question.
Q: LED turned off and it will not turn back on. What should I do?
A: Sometimes you need to "reset" the circuit after it is exposed to a very strong positive field, which can actually cause the LED to turn off. Try tapping the free resistor lead directly with your finger or bringing an object with a strong negative field very close to the antenna. If that still does not work, try removing the circuit components one at a time and re-inserting them into the breadboard.
Q: The behavior of my charge detector is not consistent. What can I do to improve it?
A: This charge detector circuit is very sensitive. There are numerous factors in your environment that can affect buildup of static electricity on your body and the objects surrounding you, like the humidity, how sweaty your hands are, the clothing you are wearing, and the surface you are standing on. If other objects nearby have strong electric fields, this can make it difficult to measure the effect of a single item that you bring near your circuit. Do your best to do the experiment all at once while standing in one place (for example, avoid walking around a carpeted room in socks while doing the experiment). You can also periodically discharge yourself by touching a large metal object.
Q: My LED does not turn on at all. What is wrong?
A: Make sure you have the polarity of the LED correct. LEDs are like one-way valves for electricity. They have a positive end (the long lead) and a negative end (the short lead). If they are connected backwards, no electricity can flow through them and they will not light up. In this project, the long lead goes into breadboard hole B3 and the short lead goes into B4.
Q: I learned that you always need a resistor in series with an LED in order to prevent it from burning out. Why doesn't this circuit have a current-limiting resistor?
A: The transistor in this project has a built-in current-limiting capability. See Static Electricity Sensor from the bibliography for a more detailed explanation. In general, however, it is always safest to include a current-limiting resistor with an LED.
Q: I smelled smoke when I connected the battery and now my circuit does not work.
A: It is possible to damage both the transistor and the LED by connecting the 9 V battery incorrectly. Make sure you follow the breadboard diagrams carefully. Your kit contains 10 LEDs, so if you burn out an LED you can replace it. However, your kit only contains one transistor. If you burn out your transistor, contact us at scibuddy@sciencebuddies.org for a replacement.


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If you have purchased a kit for this project from Science Buddies, we are pleased to answer any question not addressed by the FAQ above.

In your email, please follow these instructions:
  1. What is your Science Buddies kit order number?
  2. Please describe how you need help as thoroughly as possible:


    Good Question I'm trying to do Experimental Procedure step #5, "Scrape the insulation from the wire. . ." How do I know when I've scraped enough?
    Good Question I'm at Experimental Procedure step #7, "Move the magnet back and forth . . ." and the LED is not lighting up.
    Bad Question I don't understand the instructions. Help!
    Good Question I am purchasing my materials. Can I substitute a 1N34 diode for the 1N25 diode called for in the material list?
    Bad Question Can I use a different part?

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General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "Avoid the Shock of Shocks! Build Your Own Super-sensitive Electric Field Detector." Science Buddies, 8 Sep. 2023, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p050/electricity-electronics/electric-field-detector. Accessed 4 Mar. 2024.

APA Style

Science Buddies Staff. (2023, September 8). Avoid the Shock of Shocks! Build Your Own Super-sensitive Electric Field Detector. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p050/electricity-electronics/electric-field-detector

Last edit date: 2023-09-08
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