Chapter 18: Electric Charge
18.A: Static Electricity
- Static Electricity
- An imbalance of electric charge within or on the surface of an object.
- Law of Charges
- The principle stating that like charges repel and unlike charges attract.
- Electric Conductor
- A material that allows electric charge to move easily through it, such as metals.
- Electric Insulator
- A material that does not allow electric charge to move easily through it, such as rubber and glass.
- Semiconductor
- A material whose electrical conductivity can be controlled by impurities, temperature, or electric fields.
Historical Context
- The Greeks observed static electricity as early as 600 BC using amber.
- William Gilbert coined the term "electricus" and conducted early experiments on electricity.
- In the 1700s, the Leyden jar was developed to store electric charge.
- Benjamin Franklin introduced the terms "positive" and "negative" charge.
Discovering Electric Charge
- Electron
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J.J. Thomson discovered negatively charged particles in 1897. These particles were named electrons.
- Fundamental Charge
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Robert Millikan's oil drop experiment identified the magnitude of the fundamental charge of an electron: \( -1.6 \times 10^{-19} \, \text{C} \).
- Coulomb (C)
- The SI unit of electric charge, equivalent to the charge transported by one ampere in one second.
Faraday Cage
- Invented by Michael Faraday in the 1800s.
- Protects its interior from external electric fields by redistributing charge on its surface.
- Applications include protecting sensitive electronics and shielding car occupants from lightning strikes.
Questions for Students
- Define static electricity and explain how it is created.
- State the law of charges and provide an example of its application.
- Describe the difference between conductors, insulators, and semiconductors.
- What is a Faraday cage, and how does it protect its interior from electric fields?
- Explain the significance of Millikan’s experiment in understanding electric charge.