EM Waves 04 
OPENING QUESTION:
═══════════════════════════ LEARNING TARGET: I will be able to diagram how each type of light in the electromagnetic spectrum is created HERE ON EARTH. WORDS O' THE DAY:
FORMULAE OBJECTUS:
WORK O' THE DAY: ═══════════════════════════ Let's volunteer some folks to get their opening ?'s up on the board... Now let's have a wee bit of fun with light. We have talked about the very odd concept that a photon of light has Zero mass. However, a photon of light very definitely has momentum (remember how gamma rays are used to zap cancer cells?): Work with your group to see if you can derive a formula for the "equivalent" mass of a photon (sometimes referred to as a "rest mass" but that is rather misleading, since photons don't ever 'rest')
═══════════════════════════ Hint: E = mc^{2} ═══════════════════════════
Once you have the "equivalence" formula derived, please use it to find the "equivalent" mass of each of the two photons discussed in today's opener. Now let's talk about what those formulae mean: E = mc^{2} is one of the most (if not THE MOST) easily recognizable formula in all of science. Generally stated, it says that energy and mass are interchangeable. That is by way of saying that we can determine the amount of energy released when a certain amount of mass is converted into energy... That may seem AWFULLY theoretical until we look at THIS: The "Tsar Bomb" was the largest nuclear detonation every achieved. It was the heart of the "Cold War" and the Soviets designed a bomb that would be equivalent to 100 million tons of TNT. Either the bomb didn't *quite* go off as calculated or the Soviets got nervous and backed it down by about half (I've read both happend, I dunno). Anywho... Let's do some math: 1.000 kiloton yield = 4,184,000,000,000 joules of energy = 4.184 x 10^{12} J 58.00 megatons = 58,000 x 1.00 kt => (5.8 x 10^{3} kilotons) x (4.184 x 10^{12}J) = 2.427 x 10^{17} J Now let's work backwards using E = mc^{2}: E = mc^{2} Isolate for mass: E/c^{2} = m Substitute for c (speed of light) and E (energy of the Tsar Bomb calculated in Joules above): (2.427 x 10^{17} J)/(3.00 x 10^{8} m/s)^{2} Do the math: 2.70 kg of mass turned into energy
