Have you wrapped your mind around static electricity yet? You should understand by now how scuffing along a carpet in socks builds up electrons, which eventually jump off in a flurry known as a spark. And you also probably know a bit about magnets and how magnets have north and south poles AND a magnetic field (more on this later). Did you also know that electrical charges have an electrical field, just like magnets do?

It’s easy to visualize a magnetic field, because you’ve seen the iron filings line up from pole to pole. But did you know that you can do a similar experiment with electric fields?

Here’s what you need:

• dried dill (spice)
• vegetable or mineral oil
• 2 alligator wires
• static electricity source (watch video first!)

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Download Student Worksheet & Exercises

Here’s what you do:

1. Fill a saucer with vegetable or mineral oil.
2. Sprinkle small seeds or spices on top, such as caraway, anise, or dill (this one works best).
3. Build up an electric charge by either rubbing a balloon on your head, rubbing a PVC pipe with a wool sweater or mittens, or your favorite way to build up to a spark.
4. Bring the charged object near the oil – what happened to the spices?
5. Does it matter which end of the balloon/pipe/etc you hold near the oil? What if you move it a bit near the dish?
6. Stir the dill into the oil. Bring a charged object near and watch the dill spring up to touch the rod.

Troubleshooting:
If your dill isn’t moving at all, your object may be too ‘dirty’ (e.g. have too much oil from your fingers) on it to hold a charge. Clean it with rubbing alcohol after you use soap and water, and you should see better results.

What’s going on?
The dill/caraway/anise are all shaped like rods, which move to line up in the field (which is why round particles like cinnamon and pepper don’t work as well). The dill has a balance of charges – both plus and minus – and when you bring a charged object close, the negative charges in the dill are attracted to the balloon but the positive charges are repelled, so one side of the dill becomes minus and the other plus. Since the dill is free to move in the liquid, it lines up in the electric field to indicate the charge direction.

If you move the balloon just right, the attractive electrical charge will pull the lightweight dill right up out of the oil and onto the balloon. Have fun!

Exercises

1. What happened when you brought a charged balloon near the dill?
2. What side of the dill was attracted to the balloon?
3. What happened when you brought two negative charges near the dill?
4. Were you able to make the dill come out of the liquid and onto the balloon without touching the oil?

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Click here to go to next lesson on Weird Shapes and Field Lines.