Spring Semester, 2004
Objectives.
(S) Radiation III: Types, Backgrounds, and Space Radiation [AF/MW].
[1] Know what cosmic rays are, and know where they come from. Realize that dominant components of cosmic rays are protons and electrons.
[2] Be able to describe how the Earth's magnetic field shields its surface from cosmic rays. Be able to contrast this with the mechanism by which the Earth's atmosphere shields its surface from X-rays and gamma rays.
[3] Know that there is an inverse relationship between cosmic ray activity at the Earth and sunspot activity. Be able to explain the origin of this relationship.
[4] Know what the Van Allen Belts are, and know what the South Atlantic Anomaly is.
[5] Be able to describe a few countermeasures that can be taken to help protect spacecraft from radiation damage.
(T) Sonoluminescence [BL].
[1] Realize that sonoluminescence is the name for any process in which sound is converted into light. Realize that this light production, like any light production, must ultimately come from the acceleration of charges.
[2] Know that sonoluminescence is remarkable because it involves an increase in the wave energy density by factors of approximately 1011 in converting sound into light.
[3] Know that the mechanism by which sound waves stimulate light production appears to involve the violent collapse of bubbles, during which time the bubble innards are heated to extreme temperatures.
[4] Realize that the spectrum of light emitted by a collapsing bubble looks roughly similar to that emitted by a black body {Black Body Radiation}. Know that, from an analysis of this spectrum, it is not uncommon to find bubbles with interior temperatures of 10,000° C.
[5] Realize that one reason that sonoluminescence is such a hot topic is because of claims that it can be used to initiate fusion. Thus, the process is often touted as a "star in a jar".
(U) Introduction to General Relativity [JE].
[1] Know that the key idea behind the theory of general relativity is that one cannot distinguish gravitation from acceleration.
[2] Know that in general relativity there is no "force of gravity"; all objects simply move on "straight lines" through spacetime. Because that spacetime is sometimes curved, we perceive some objects to move on curved lines [but they don't really], and we attribute this curvature to a force of "gravity" [which doesn't really exist].
[3] Know that it is the presence of mass and/or energy that causes spacetime to curve.
(V) Gravitational Waves [DP].
[1] Realize that whenever any mass accelerates, gravitational waves are emitted.
[2] Recognize the close parallel between electromagnetic waves [light] and gravitational waves: accelerating charges produce light; accelerating masses produce gravitational waves.
[3] Understand that gravitational waves are ripples in spacetime itself that propagate across the universe at the speed of light.
[4] Realize that gravitational waves have not yet been detected. Understand that this is simply because they are so very weak.
[5] Know that LIGO, a gravitational wave detector with sister sites in Washington state and Louisiana, is currently searching for gravitational waves.
(W) Black Holes [JE].
[1] Realize that every massive body has a Schwarzschild radius, a quantity that is proportional to the mass of the body.
[2] Realize that if all of the mass of a body is squeezed within its Schwarzschild radius, the body will undergo gravitational collapse and will become a black hole.
[3] Know that the Schwarzschild radius of the Earth is only about 1 cm. Thus, gravitational collapse of the Earth would be pretty tough to accomplish.
[4] Realize that, surrounding a black hole, there is an invisible boundary called an "Event Horizon". Any material that crosses the event horizon will never escape from the black hole.
[5] Know that, if you were to watch an object fall into a black hole, you would never see it actually cross the event horizon. The object would appear to slow down, dim, and become redder as it approached the horizon, but you would never see it actually cross.
[6] Realize that the effects described in Objective [5] above are due to the fact that light cannot escape from within the event horizon. From the perspective of the object falling into the black hole, there is no slowing. The object simply zips right across the boundary.
(X) Chaos [DP].
[1] Realize that the hallmark of a chaotic system is its sensitivity to initial conditions. That is, starting the system off in a slightly different manner will rapidly lead to drastic differences in outcome.
[2] Be able to give examples of both chaotic and non-chaotic systems.
[3] Realize that a chaotic system is distinguished from a truly random system by its predictability. A chaotic system is completely predictable; it's just extremely difficult to predict its behavior over long periods of time. A random system, on the other hand, is completely unpredictable {by definition}.
(Y) Electromagnetic Compatibility [DL].
[1] Know that the field of Electromagnetic Compatibility [EMC] in concerned primarily with studying the ways in which devices producing electromagnetic waves affect other devices.
[2] Be able to describe briefly how cell phones work.
[3] Know that every piece of the Electromagnetic Spectrum between 5 KHz and 300 GHz has been assigned a primary user, and that this upper limit is continually rising. Recognize that this upper limit frequency is now only a factor of 1000 lower than visible light!
[4] Be able to explain why the risk of cancer due to exposure to X-rays is so much greater than that due to exposure to RF [radio-frequency] waves, even when the RF waves contain greater total energy.
[5] Know that, in order to transmit a signal faithfully, there is a lower limit to the width of the band that can be used. Know what this limit is.
[6] Know that, as of June 1, 2004, companies have been authorized to provide broadband internet access over power lines. Know that this poses somewhat of a risk of interference with other RF devices, and know that for this reason, several countries (including Japan) have outlawed this practice.
(Z) Extrasolar Planets [CH].
[1] Know approximately how may different extrasolar planets have currently been discovered, and know that the first was discovered in 1994.
[2] Know that the existence of extrasolar planets must be inferred indirectly. Know that this is because any light that they reflect is completely dwarfed by the light emitted by their star.
[3] Be able to explain how the technique of photometry may be used to infer the existence of an extrasolar planet.
[4] Be able to explain how the technique of astrometry may be used to infer the existence of an extrasolar planet.
[5] Be able to explain the relevance of measuring Doppler shifts when it comes to hunting for extrasolar planets.
[6] Know that, in April of 2004, the first extrasolar planet ever found by gravitational microlensing was announced. Be able to briefly describe how this technique works.