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Ben Franklin and Electricity

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(Previous post about Young Ben Franklin)

1746 Began his First Experiments with Electricity
1747-1748 Retired from active Business to Continue Electrical Experiments and Pursue Public Service
1749 Helped Found the Pennsylvania Academy (which later became the University of Pennsylvania)
1750-1764 Served on the Pennsylvania Assembly and helped found the Pennsylvania Hospital, America's first charity hospital. Established the First Fire Insurance Company in North America. Appointed Deputy Postmaster General of North America. Wrote a plan for a union of the colonies for security and defense.
1752-1754 Conducted Famous Kite Experiment.  Erected Lightning Rods in Philadelphia.  Received the Copley Medal of the Royal Society of London for Research in electricity.


Everyone is familiar with Franklin's kite flying electricity experiment in which he proved that lightning and electricity are the same thing. Franklin's discoveries about electricity went far beyond lightning, however. At the time Franklin was conducting his experiments, people believed that there were two kinds of electricity, one kind that attracted objects and another kind that pushed objects away. Franklin was able to prove that they were the same force and this understanding later led to the invention of the battery, the electric motor and alternating electric current. He didn't know, however, the causes of electricity because it was not understood at this time on the atomic level. Even detecting electricity can be difficult, since you can't see or hear it, but you sometimes can see the effects of it. Most of Franklin's experiments were on static electricity, so let's see what we can learn about electricity by looking at static electricity.
You will need two balloons for this demonstration. Tie some thread onto one of the balloons and attach the other end of the thread to the ceiling with some tape, so that the balloon hangs from the thread. You want it to hang about chest level. Rub the balloon that is hanging in your hair, so that it picks up some electrical charge. Take the other balloon and rub it in your hair also. 
Now hold the second balloon in both of your hands and slowly bring it close to the balloon that is hanging. When the balloons are rubbed in hair, they pick up some stray electrons from the hair, causing the balloons to pick up a negative charge. When brought close to each other, they will repel because like charges repel one another.
Now, take a piece of clear tape and tape it to the top of a table, leaving a little part loose so it can be removed quickly. Quickly rip the tape off the table and holding it at both ends, hold it near the balloon with the sticky side facing the balloon. When ripping the tape off, the tape loses negative charges because the tape leaves electrons behind in the sticky residue left on the table, making it become positively charged. When held up to the balloon, which is negatively charged from rubbing it in hair, it is attracted to the positively charged tape, because opposite charges attract one another.
There are two ways that atoms gain or lose electrons. To see the different ways, we made an electroscope. To make one, you will need a glass, a plastic lid that is bigger than the mouth of the glass, a paper clip or non-coated wire, two small thin strips of aluminum foil and a balloon. 
Take the wire or paper clip and twist it into a shape with a circle at the top and two hooks underneath. Cut a slot in the plastic lid and slide the end of the wire with the hooks on it through the slot and turn it 90 degrees so that the circle holds the wire in place. Hang the two strips of foil on the hooks. Place the lid on top of the glass, so that the foil strips hang inside the glass.
 Rub the balloon in your hair as before, to give it a negative charge. Bring the balloon close to the wire. It might look like the balloon is touching the wire in this picture, but it isn't really. You should just get the balloon close to the wire, not touching it. The foil strips should move away from each other because the negative charge of the balloon will repel the negatively charged electrons in the wire and foil strips. Since they are repelled, they travel away from the balloon, causing the foil strips to be rich with electrons, which causes the foil strips to repel one another.
If you move the balloon away, the foil strips should relax again. Once the negatively charged balloon is moved away, the electrons in the foil strips are able to travel back up into their normal position, and the positive charges in the paper clip travel back to their normal position, making everything neutral again.
If you repeat the experiment but this time let the balloon touch the wire, the foil strips should begin to stay pulled apart, even after you remove the balloon. By touching the balloon to the wire, some of the balloons extra electrons were able to travel into the paper clip and flow into the foil strips, causing a permanent negative charge.Since the foil strips stayed negatively charged, the stayed away from each other. This is called charging by conduction.
Next, bring the balloon close to the wire, and touch the wire with the finger from your other hand. The foil strips should relax. Then, at the same moment, pull both the balloon and your finger away. The foil strips should move away from each other again. Like in the previous experiment, when the balloon was moved near the wire, the electrons in the wire and foil moved, concentrating the negative charges into the foil, causing them to repel each other, however when you touched your finger to the wire, the electrons could travel farther away from the balloon by traveling through your finger up your arm. The electrons then moved from the wire and foil strips and when you moved both the balloon and your finger away at the same time, the wire and foil were left with fewer electrons than they should have, giving the foils an overall positive charge, moving them away from each other. When charging so that the resulting charge is opposite of the charge you used, it is called charging by induction.

Science Sunday

3 comments:

  1. How fun is that! We'll have to give it a try.

    ReplyDelete
  2. I"m going to have to reread this when I'm not brain dead because it looks really cool.

    ReplyDelete
  3. My Little J would think this was really cool! I'll have to plan on doing this with him sometime.

    ReplyDelete

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