Using Historical Case Studies in Introductory Physics

Debora M. KatzUnited States Naval Academy

Annapolis, MD

Why do we teach physics to non-physicists?Physics is the fundamental Science

People use the scientific method to examine and discover the truths of the universe.

Put poetically, physics illuminates the darkness

Why are you taking this physics class?0. It’s a requirement.1. We live in a high-tech

world so we need to understand technology.

2. Physics is a tough course that is used to weed us out.

Two Views of a Physics CourseMy view My students’

Typical Physics Instruction • Dogmatic• Devoid of the

human element• Does NOT

include stories• No mistakes,

no missteps, no debate

Introduction to Case Studies•In the broadest sense, a case study is an educational story that is traditionally used in medicine, business and law education. •Case studies may be woven into traditional teaching pedagogy or developed for contemporary project-based methods. •A student working through a case study is in the role of practitioner.

Historical Case StudiesA student is in the role of a historical scientist, exploring the process by which great discoveries were made or new technologies were invented.

Ben Franklin’s Lightning RodIn the middle of the 18th century, people loved to play with electricity in their homes, but most people thought that lightning was another phenomenon altogether—explosions of atmospheric gas, something like the explosions of gunpowder.

Ben Franklin’s Lightning Rod•Benjamin Franklin thought otherwise. He believed that lightning was a colossal electrical spark just like the small sparks people found so amusing.•Franklin collected charge from his flying kite in a Leyden jar. •Franklin showed that a Leyden jar charged by clouds produced all the same effects as Leyden jars charged in the home. •So he concluded that lightning is an electrical phenomenon, like a giant spark.

Ben Franklin’s Lightning Rod• As people started building taller structures, those structures became more likely targets of lightning strikes, causing fires, destroying property and lives.Once Franklin understood that lightning was a giant spark, he invented a way to protect against lightning strikes—the lightning rod.

Ben Franklin’s Lightning RodFranklin published the following recommendations for lightning rods in Poor Richard (1753):

1. Just outside each building an iron rod should be planted three to four feet in the moist ground.

2. The rod should extend 6 to 8 feet above the tallest part of the structure.

3. On top of the rod should be a foot of brass wire sharpened to a fine point.

.

Ben Franklin’s Lightning RodThe third point—the shape of the top of the rod—was controversial. Franklin recommended that a pointed lightning rod be used, but another scientist, Benjamin Wilson, recommended a blunt-end lightning rod. The Royal Society of London was asked to evaluate the recommendations and decide which would make a better device.

Your goal in this case study is to decide between Franklin’s lightning rod and Wilson’s.

Ben Franklin’s Lightning RodIn order for air to break down and become a conductor, the electric field in the air must be 3 × 106 N/C. Let’s assume that in order for a lightning rod to work, the electric field at its surface must equal that breakdown electric field. Calculate the amount of charge on the surface of each conductor. The one with the least amount of charge is the better design, because a smaller amount of charge on the surface of the conductor means a smaller amount of charge travels through the air.

A Student’s Response to Case Studies

Professor Katz,

I am really glad you enjoyed my project! It's one of the few things I did right in the many technical courses here at the Academy lol I really did love doing it and I hope your students have enjoyed working on their projects also! I am sorry you cannot make it but hopefully some people from your department will be able to go. I hope all is well! You are a great teacher and your students are lucky to have you as a Professor!

Very Respectfully,

Michelle

A few references:1. Stealing God’s Thunder, Philip

Dray 20052. Make to Stick, Chip Heath and

Dan Heath 20073. Science Teaching: The Role of

History and Philosophy of Science, Michael R. Matthews 1994 (2000)

Debora KatzPhysics DepartmentUnited States Naval AcademyAnnapolis, MD 21402

dkatz@usna.eduhttp://www.usna.edu/Users/physics/dkatz/

My Contact information:

Using Historical Case Studies in Introductory Physics