What You Should Know from “Light as a Wave”! 1.) Classically, what is a wave? A wave is a disturbance that moves through a medium. (You can’t have a wave without a medium.) 2.) What was the name of the experiment that convinced the scientific world that light was a wave? Young’s experiment 3.) Of what did the experiment alluded to in #2 consist? When light passes through a double slit in “Young’s experiment”, it is found to produce interference patterns on the other side. These interference patterns were “proof” that light was a wave. 4.) What problem do we run into if we assume that light is a classical wave? Light travels 93,000,000 miles through empty space to reach the Earth. If light is a classical wave and a wave is a “disturbance that moves through a medium,” where is the medium in space through which light waves travels? 1.)

6.) How is the direction of an electric field defined? 5.) Free charge will produce an “electrical disturbance” in the region around it. The amount of “force per unit charge” available at a point due to that charge is defined as what? This is the definition of an electric field. 6.) How is the direction of an electric field defined? It’s the direction a positive test charge would accelerate if put in the field at the point of interest. 7.) What produces magnetic fields? Charge in motion. 8.) How is the direction of a magnetic field defined? Direction a compass points. 9.) What is light (the long answer)? An alternating electric field and an alternating magnetic field oscillating at right angles to one another as the wave moves through space at the “speed of light.” 10.) What is light (the short answer)? An electromagnetic wave. 2.)

11.) What is the difference between a radio waves and a light wave? Both are electromagnetic waves and both travel at the speed of light. Their only differences are in how they are produced and their frequency. 12.) The earth’s magnetic field has what kind of pole in the north geographic hemisphere? It’s a south magnetic pole. 13.) Where is the earth’s magnetic pole in the northern hemisphere? Hudson Bay area. 14.) Has the earth’s magnetic field always been like it is today? No. It switches directions every 300,000 to 400,000 years. 15.) Solar winds (and storms) interacting with the earth’s magnetic field and atmosphere produce what? Northern and southern lights (the aurora borealis). 3.)

11.) So how does light as a wave move through empty space? Changing electric fields induce magnetic fields, and changing magnetic fields induce electric fields. As an electromagnetic wave is a changing magnetic and electric field moving together synchronously (i.e., in lock step), the changing magnetic part of the field feeds the electric field and the changing electric part of the field feeds the magnetic field. In other words, the electromagnetic wave is its own medium. 4.)