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Transcript of Static Electricity
Law of Electric Charges
A charged object exerts an electric force (i.e., force of attraction (pulling together) or repulsion (pushing apart)). NOTE: The strength of the electric force is related to two factors: (1) amount or size of charge on each object and (2) distance separating the objects.
The Law of Electric Charges states
Objects with like charges repel each other
Objects with opposite charges attract each other.
Types of Static Electricity
There are three types of static electricity:
Charging by friction (contact)
Charging by conduction (contact)
Charging by induction (no contact)
Charging by Conduction
Everything is made of matter. Matter is atoms, and atoms consist of subatomic particles: protons (+), and neutrons (0) inside a nucleus, plus electrons (-) in energy shells outside the nucleus.
Charging by Induction
Charging by Induction is charging a neutral material by bringing another charged material CLOSE TO BUT NOT TOUCHING a neutral object.
In this process when the charged material is brought near the neutral material, it causes (induces) the electrons in the neutral object shift position (....recall, once again, the Law of Electric Charges of attraction and repulsion). If the charged material has a negative charge (i.e., more electrons than protons), the electrons in the neutral material move away (....because like charges repel). This is a separation of charges in the neutral material. That is, one side of the material is negative and the other side is positive. NOTE: The neutral material remains neutral. Why? No new electrons move into the neutral object. The number of electrons and protons is unchanged. Once the charged material is moved away, the electrons redistribute evenly throughout the neutral material and the separation of charges "disappears."
Grounding is connecting an object to a large body (e.g., Earth) so that the charge in the object is absorbed by the large body.
Using the diagram, explain how you could charge an object permanently by induction.
Static electricity is an imbalance of electric charge on the surface of an object.
NOTE: Static electricity needs an insulator and a conductor.
An insulator is a material that does NOT allow electrons to move through it freely. Rather, the electrons are stuck in one place and do not move around (...hence, static). A rubber balloon is an insulator.
Conductors is a material that lets electrons move through it freely. Some metals are conductors. Negative charges do NOT build up on conductors.
When there is a difference in NEGATIVE CHARGES, charges will move ...from a place of high negative charge to an area of low negative charge.
Charging by Friction
Charging by friction occurs when two neutral materials rub together (i.e., friction) so that electric charges are transferred from one material to the other material. The material "taking" electrons becomes negatively charged while the material "giving" electrons becomes positively charged.
In the above illustration, the rubber balloon and the human are neutrally charged (i.e., #p+ = #e- in both materials). When rubbed together, the electrons move from the human head into the rubber balloon. With more electrons, the rubber balloon becomes negatively charged. The human head has given away electrons. The head is positively charged.
Why does the movement of electrons occur?
If the number of protons equals the number of electrons (+ = -), the atom does NOT have a charge.
If the number of protons and electrons is not equal, the atom has a charge. If the number of electrons is greater than the number of protons, the atoms has a negative charge.
Can you describe how static electricity forms lightning? It looks easy, but much more is happening than you think. Insert your ideas here....
This is Charging by Friction.
Can you explain the process?
The Triboelectric Series lists materials in order of their tendency to gain electrons. In the illustration, materials at the top of the series tend to lose electrons, and as you move down the list, the materials tend to gain or attract electrons. Why? It is due to electronegativity. Materials with a high electronegativity attract and hold electrons tightly. A low electronegativity material does not hold electrons tightly....electrons, in this case, are given away.
Charging by Conduction
Charging by Conduction also involves contact (i.e., two materials must touch). However, the materials are NOT rubbed together to create friction. Rather, one material may have a charge while the other material in neutral (i.e., no charge). If the charged material has a negative charge (i.e., more electrons than protons) and touches the neutral material, electrons in the neutral material move away due to the Law of Electric Charges (...like charges repel). The neutral object has a separation of charges (...one side is negative and the other side is positive. The electrons in the charged material are attracted to the positive charges in the neutral material (...again Law of Electric Charges where opposite charges attract). Electrons move into the neutral material from the charged material. Now, the neutral material has more electrons than protons.....a charge imbalance....and the material is now negatively charged. When the two materials are separated, the negative charge remains permanently in the second material.
Charging by Conduction does not always involve a charged object and a neutral object. Both materials could be charged. In this situation, electrons will always move from the material with the larger negative charge to the material with the smaller negative charge.
Can you explain this movement of electrons?