Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards


Electric Charge and Static Electricity

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:

Electric Charge and Static Electricity
Students should observe direct electrical properties of matter, such as static electricity and conductivity. (b) At this level, students should review fundamental observations of electric charge and develop an understanding of how we know that there are only two kinds of electric charge. They should observe that two objects of the same material treated the same way to become charged repel each other, and that only when two objects of the same material are treated differently to produce charges do they attract each other. (Depending upon the treatment, two objects of the same material but treated differently may attract each other or repel each other, but two objects of the same material will never attract each other if they are treated the same way.) They should learn that negative charge is defined as the charge of a rubber rod rubbed with fur.No attempt should be made at this level to discuss electrons or protons. Instead, students should concentrate on the basic idea of two kinds of electrical condition called plus and minus. They should learn the difference between conductors and insulators in terms of their ability to transfer charge from one object to another. The history of electricity is a rich source from which to draw when examining various models of electricity and testing them through observation. Students should use electroscopes as a means of observing effects of charges.


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