Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards


Coulomb's Law and Induced Polarization

Electric Force: Coulombís and Gaussís Laws
The electric force is a universal force that exists between any two charged objects. Opposite charges attract while like charges repel. The strength of the force is proportional to the charges, and, as with gravitation, inversely proportional to the square of the distance between them.


Further Description:

Electric charge must be defined in terms of observations of interactions of charged objects. It is quite remarkable that in this high-technology age, the negative charge is still defined as the charge given to a rubber rod that has been rubbed with fur, and a positive charge is still defined as the charge given to a glass rod that has been rubbed with silk.

The nuclear model of the atom allows us to create a model of electricity based upon electrons, protons, and ions. Explanations can then be made in terms of these ideas. The chain of evidence up to and including Millikanís experiment and the work leading to Coulombís and Gaussís laws are fundamental.


Concepts Needed:

Grade 9

Electroscope, charge, electrostatics, conductor, insulator

Grade 10

Galvanometer, induction, polarization, ground

Grade 11

Charges on fundamental particles, electron, proton, neutron, ion, coulomb

Grade 12

Polarization as a vector, vector electric fields


Empirical Laws or Observed Relationships:
:

There are only two kinds of electric charge, which we define as plus and minus; opposite charges attract and like charges repel; electrically induced polarization; induction; the force between two point charges (or charges on spherically symmetric objects) is inversely proportional to separation and directly proportional to the product of their charges; electric charge is quantized, the electronic charge being the smallest stable electric charge found in matter; conservation of electric charge


Theories or Models:

Rutherford model of an atom, Gauss=s law


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Micro-Unit Description:

Coulomb's Law and Induced Polarization
At this level, students should examine the process of induced polarization, creating their own models to account for what they observe. This provides an opportunity to postulate the existence of a negative or positive charge that moves in or on a metal-coated object to produce that polarization.Various demonstrations or experiments involving charging conductors by induction should be carried out to give students opportunities to explain such phenomena with testable hypotheses. Students should explore the quantitative aspects of electric charge, including Coulomb's law as a proportion (not using the constant, k).


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