Electroscopes are scientific instruments designed to detect and measure the electric charge on an object. For the instrument described here, objects brought close to the copper coil induce a charge in the coil and connected aluminum foil leaves. The foil leaves then repel each other and, with the aid of the clinometers, the extent of repulsion can be recorded.
- Petri dish lid
- Beaker (250 mL) or comparable glass container
- Copper Wire, large gauge
- Aluminum foil
- Adhesive, quick dry (e.g. hot glue)
- Clinometers (downloadable link)
- Drill with drill bit
- Wood/Metal (to place dish on while boring hole)
- Needle nose pliers
- Scotch Tape
- Hole punch or pencil
- PVC tube
- Glass rod/stirrer
- Wood dowel
- Wool cloth
- Cotton cloth
- Polyester cloth
- Ensure that your petri dish, either the top or bottom, fits around the top of your beaker.
- Place the petri dish flat side down on a sacrificial piece of wood or metal and use either a drill press or hand drill to bore a hole in the center. Use a drill bit which is slightly wider than the diameter of your copper wire.
- Cut a 15-20 cm length of wire and, using needle nose pliers, bend the top half into a spiral perpendicular to the rest of the wire.
- Insert the straight end of the wire into the hole in the petri dish. Use the needle nose pliers to bend the end of the straight half of the wire into a hook.
- Use fast acting adhesive such as hot glue to fix the wire in place on the petri dish with the spiral 1-2 cm away from the flat side. It might be easier to rest the flat side of the dish on the copper wire roll or roll of tape with the spiral positioned downward to hold the setup in place while the glue dries.
- Once the glue is dry, place the petri dish and wire combo over a beaker or glass jar and secure the wire with glue on the side with the spiral.
- Fold a flattened piece of aluminum foil in half. Using a hole punch or pencil, create a hole slightly wider than the diameter of your wire, with the edge of the hole 1-2 mm away from the folded end of the rectangle. Cut the aluminum foil into a 1 cm by 2 cm rectangle with the hole centered. Separate the two pierced rectangles of foil by cutting along the fold.
- Cut out the clinometers with scissors. (also linked in the Materials section)
- Bend the top end of the angle gauge to create a flat area where you can tape the angle gauge to the petri dish. The dot in the center of the angle gauge should be directly behind the apex of the hook. Ensure that the paper is parallel to the hook and separated by a 1-3 cm gap.
- Hang the two aluminum foil leaves on the copper wire hook.
- Place the entire assembly on the beaker and proceed to the activity.
Make sure to GENTLY touch the spiral to ground the electroscope before testing each material!
- Take your PVC tube and discharge it either by grounding it to bare metal or rinsing it off with water. Now bring it closer to the spiral of the electroscope. What happened to the foil rectangles? Why?
- Gently touch the copper spiral to discharge the electroscope. Then charge the PVC tube by rubbing it with a cotton cloth and then bring it close to, but not touching, the copper spiral. What happened when the rod approached the spiral? What angle did you measure for the aluminum foil leaves? What happens when you bring the cotton cloth close to the spiral?
- Repeat step 2 using wool, instead of cotton. What angle did you measure? If it’s a different angle than you measured in step 2, why do you think it was different? (hint: look at the triboelectric series) What happens when you bring the wool close to the spiral? Did you observe or measure any difference compared to the cotton? Why or why not?
- Repeat steps 2 and 3 with the glass rod, wooden stick, and polyester cloth. Make sure to record your angle measurements and to ground the electroscope between each test.
- Compare your measurements and observations with a neighbor. Do you have different measurements? What could cause these differences? How could you modify the experiment to produce more consistent results?
Triboelectric Series Charts
Video showing electroscope construction and use
https://www.youtube.com/watch?v=ViZNgU-Yt-Y(electroscope begins at 4:08)
Other resources for alternative electroscope designs and activities