Transcript CH-12 S2009
CH-12: Electrostatic Phenomena • • • • • Electric charge Conductors & Insulators Electrostatic force: Coulomb’s law Electric Field Electric potential How do objects acquire charge? Negative charge = electron Positive charge = an atom with missing electron E3:Two steel balls i Electroscope Like charges repel and unlike charges attract each other. Conductors and Insulators Substances that readily conduct electric charge are called electrical conductors. Conductors have free electrons, which conduct the electricity. Examples: Metals such as copper, aluminum, silver, and gold. Materials that conduct electric charge poorly are known as electrical insulators. Examples: Rubber, plastics, and wood. Semiconductors are materials whose conductivity can be controlled. Examples: Silicon, germanium. Charging by Contact and by Induction An object can be charged by two methods: -By contact. -By induction. Charging By Contact Charging By Induction Coulomb's Law The magnitude F of the electrostatic force exerted by one point charge on another point charge is directly proportional to the magnitudes q1 and q2 of the charges and inversely proportional to the square of the distance r between them. E6: The Electric Field The electric field is present in any region of space if there exists electric forces. These electric forces can be detected using a test charge. Test charges are theoretical positive charges that do not alter the electric field to be detected. Electric field at a point in space is defined as the force per unit test charge placed at that point. E10: F E . q Electric Field Lines Electric Potential Lightning