Matthew has a Master of Arts degree in Physics Education
Have you ever taken clothes out of the dryer and found them stuck together? Maybe you noticed that when you peeled them apart you heard a soft ripping sound, and you felt that the clothes wanted to stay together. The ancient Greeks noticed something similar after they rubbed amber (solidified tree resin) with a piece of cloth -- the amber had the ability to attract small pieces of dried leaves or particles of dust.
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At the end of the 1800s, it was thought that electricity was a type of fluid that was transferred between objects and caused attraction and repulsion between the objects. We now know that the transfer of electrons to and from objects creates the two types of electric charge, negative and positive. Electrons (whose name comes from elektron, the Greek for amber) are negatively charged. They exist in the outer part of atoms, and are electrically balanced by the positively charged nucleus, making the atom electrically neutral. Negatively charged particles (anions) have an excess of electrons, and positively charged particles (cations) have a deficit of electrons. When an object has more anions, it is negatively charged. You can move electrons around by performing some simple experiments.
If you take some wool and rub it onto a plastic rod, the plastic rod will strip electrons away from the wool, leaving it positively charged. The amount of negative charged gained by the plastic rod is the exact amount of positive charge the wool now possesses.
Rubbing silk on a glass rod has the opposite effect. The silk strips off electrons from the glass, and becomes negatively charged, while the glass becomes positively charged. In both cases, the total electric charge is conserved. No new charge is ever created, it is only transferred from one object to another. Benjamin Franklin came to this realization, and it is called the conservation of electrical charge.
In terms of electric charge, opposites attract and likes repel. If two positively charged particles are brought near each other, the electric force will cause these two particles to repel each other. If a positively charged particle and a negatively charged particle are brought close together, they will attract each other. In Diagram 1, the proximity of the positively charged rod to the metal plate on top of the jar causes the electrons in the metal strips inside the jar to move to the metal disk. This leaves the metal strips positively charged, and they move away from each other.
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A cloud-to-ground lightning bolt is a transfer of charge. Billowing clouds have updrafts and downdrafts of air. The colliding particles of water in these air streams cause electrons to be stripped off the ascending particles and accumulate on the descending particles. Thus, the bottom of the cloud starts to build up an enormous amount of negative charge. Air allows this initial separation of charge because it acts as an insulator, which prevents electrons from moving through it. On the ground underneath the cloud, electrons are repelled by the negatively charged air column, causing an area of positive charge. Eventually, the insulating properties of the air between the cloud and the ground break down, and the electrons from the cloud reach the ground in the form of a lightning bolt.
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A lighting bolt is one type of static discharge. You may have experienced a mini lightning bolt -- or caused one on purpose. When the air is dry, the rubber soles of your shoes strip electrons from the carpet you are walking on and cause you to be negatively charged. We call this charge imbalance static electricity, and it is also what causes your laundry to tend to stick together when it comes out of the dryer. When you touch a person or an object that is positively charged, a tiny spark jumps from you to the person or object. The next time you experience static discharge, you can say ''Stop stealing my electrons!''
The atom is composed of a positively charged nucleus with an equal mass of negatively charged electrons surrounding it making the atom electrically neutral. When electrons are stripped off of an object, that object becomes positively charged, and the object the electrons were transferred to becomes negatively charged. The conservation of electric charge states that electric charge cannot be created nor destroyed, -- it only can be transferred from one object to another.
Negatively charged particles have an excess of electrons, while positively charged particles have a deficit of electrons. Opposite-charged particles attract, and like-charged particles repel. Static electricity is the buildup of charge on the surface of materials. When enough charge builds up, static discharge may occur. Discharges can be as small as a spark between you and your friend or as spectacular as lightning.
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AP Physics 2: Exam Prep25 chapters | 184 lessons | 13 flashcard sets
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