11. Lesson 11: Charge It! Charges and Magnets

Electric charges, magnets, and currents.

“In the discovery of hidden things and the investigation of hidden causes, stronger reasons are obtained from sure experiments and demonstrated arguments than from probable conjectures and the opinions of philosophical speculators of the common sort….” William Gilbert, De Magnete (1600) We shift gears now to properties of matter that confused people for thousands of years. The strange attractive and repulsive natures of electricity and magnetism were thought to be entirely different but similarly eerie. We’ll work through some of the early ideas, starting with one of the first practitioners of a modern scientific approach and one who worked on both phenomena. Our outcome will be an empirical understanding of how charges, charges in motion, and magnetism appear to work together. We’ll save our modern understanding of this for another quantum mechanical day.

  Goals of this lesson:

Understanding, Appreciation, and Familiarity

I’d like you to Understand:

• How to calculate forces on charges using Coulomb’s Law

• How to determine the direction of magnetic force due to a current

• How to calculate the numbers of charged particles corresponding to a total charge in Coulombs

I’d like you to Appreciate:

• The effects that parallel currents have on one another

• The similarities between a loop of current and a magnet

• That the Earth is a magnet and what are the north and south magnetic poles

I’d like you to become Familiar With:

• The role of Gilbert in the history of physics

• The contributions of Franklin to electricity and magnetism