The Michelson-Morley Experiment

Translation: Spanish   Flashlet of the Experiment
 

Michael Fowler  U. Va. Physics  3/13/08

The Nature of Light

As a result of Michelson’s efforts in 1879, the speed of light was known to be 186,350 miles per second with a likely error of around 30 miles per second.  This measurement, made by timing ... Read more »

Frames of Reference and Newton’s Laws

Michael Fowler  University of Virginia  3/14/08

The cornerstone of the theory of special relativity is the Principle of Relativity:

The Laws of Physics are the same in all inertial frames of reference.

We shall see that many surprising consequences follow from this innocuous looking statement.

Let us first, however, briefly review Newton’s mechanics in terms of frames of reference.

... Read more »

The Speed of Light

Michael Fowler  Physics Dept., U. Va.  3/14/08

Early Ideas about Light Propagation

As we shall soon see, attempts to measure the speed of light played an important part in the development of the theory of special relativity, and, indeed, the speed of light is central to the theory.

The first recorded discussion of the speed of light (I think) is in Aristotle, where he quotes Empedocles as saying the light from the sun must take some time to reach the earth, but Aristotle himself apparently disagrees, and even Descartes thought that light traveled instantaneously.  Galileo, unfairly as usual, in Two New Sciences (page 42) has Simplicio stating the Aristotelian position,

Kinetic Theory of Gases: A Brief Review

Michael Fowler 6/5/08

Bernoulli's Picture

Daniel Bernoulli, in 1738, was the first to understand air pressure from a molecular point of view. He drew a picture of a vertical cylinder, closed at the bottom, with a piston at the top, the piston having a weight on it, both piston and weight being supported by the air pressure inside the cylinder. He described what went on inside the cylinder as follows: “let the cavity contain very minute corpuscles, which are driven hither and thither with a very rapid motion; so that these corpuscles, when they strike against the piston and sustain it by their repeated impacts, form an elastic fluid which will expand of itself if the weight is removed or diminished…&rdqu ... Read more »

How Relativity Connects Electric and Magnetic Fields

Michael Fowler, University of Virginia

A Magnetic Puzzle…

Suppose we have an infinitely long straight wire, having a charge density of electrons of –λ coulombs per meter, all moving at speed v to the right (recall typical speeds are centimeters per minute) and a neutralizing fixed background of positive charge, also of course λ coulombs per meter.  The current in the wire has magnitude I = λv (and actually is flowing to the left, since the moving electrons carry negative charge). 

Suppose also that a positive charge q is outside the wire, a distance r from the axis, and this outside charge is moving at the sam ... Read more »