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Physics 2170 Foundations of Modern Physics Special Relativity. Clicker Questions Lecture Slides Professor John Price, Fall 2014. CUClickers. You MUST register your clicker this semester even if you have do it before. Every day : set your clicker code to BB
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Physics 2170Foundations of Modern PhysicsSpecial Relativity Clicker Questions Lecture Slides Professor John Price, Fall 2014
CUClickers • You MUST register your clicker this semester even if you have do it before. • Every day: set your clicker code to BB • Wait for 1st clicker question to open • Hold down On/Off Switch 4 seconds • Flashing blue light: hit BB • Choose and answer. you’re set for rest of class period • Do not turn off your clicker during class (otherwise, repeat)
Clicker Slide 1 Physics 2170, Fall 2014 Do you have your clicker here today? a) yes b) no c) 1492 d) The Gettysburg Address e) I think so, but where are we going to get an octopus this time of night?
Clicker Slide 2 Physics 2170, Fall 2014 My major is (or is most likely) a) A&S Physics b) Engineering Physics c) Astronomy d) Other engineering e) Other A&S
How much background do you have in special relativity? • None • I have read popular books and articles on the subject. • I have studied it in a physics class before. • I could be teaching this class. • I have built a working time machine. Clicker Slide 3 Physics 2170, Fall 2014
... -3 -2 -1 0 1 2 3 ... ... -3 -2 -1 0 1 2 3 ... Galilean Relativity x t=0 x’ v=2m/s • What is the coordinate of the green ball in each frame • at time t = 2? • 1 m in S and 2 m in S’ • 3 m in S and -1 m in S’ • 3 m in S and 1 m in S’ • 4 m in S and 4 m in S’ Clicker Slide 4 Physics 2170, Fall 2014
... -3 -2 -1 0 1 2 3 ... ... -3 -2 -1 0 1 2 3 ... Galilean Relativity x t=0 x’ v=2m/s • What is the coordinate of the black ball in each frame • at time t = 2? • -2 m in S and -4 m in S’ • -4 m in S and -1 m in S’ • 2 m in S and -6 m in S’ • 4 m in S and 4 m in S’ Clicker Slide 5 Physics 2170, Fall 2014
The Ether c v Suppose the earth moves through the fixed ether with speed v. A light wave traveling at speed c with respect to the ether is heading in the opposite direction. According to Galilean relativity, what is the speed of the light wave as viewed from the earth? a) c b) c+v c) c-v Clicker Slide 6 Physics 2170, Fall 2014
The Ether c v Suppose the earth moves through space with speed v. A light wave traveling at speed c with respect to faraway stars is heading in the opposite direction. According to Einstein’s relativity, what is the speed of the light wave as viewed from the earth? a) c b) c+v c) c-v Clicker Slide 7 Physics 2170, Fall 2014
The speed of light in vacuum is 3.0X108 m/s. About how long does it take light to move the length of your arm? a) 2ms (10-3 s) b) 2ms (10-6 s) c) 2ns (10-9 s) d) 2ps (10-12 s) Clicker Slide 8 Physics 2170, Fall 2014
Maxwell equations are not Galilean invariant • Galilean relativity: • satisfiedby Newton’s lawsof mechanics F = ma • violated by Maxwell’s laws description of light (E&M) E&M waves: James Clerk Maxwell 1831-1879 Maxwell’s equations: oscillating E and B fields
Time Measurement in Special Relativity Reference Framewith Synchronized Clocks Bang! That’s an “event” with a location and a time measured locally
Time Measurements In a given reference frame, the time of an event is given by • The time the observer at the origin sees it. • The time that any observer anywhere in the frame sees it. • The time according to the clock nearest the event when it happens. • The time according to a properly synchronized clock nearest the event when it happens. Clicker Slide 9 Physics 2170, Fall 2014
Q: Two lights (some distance apart on a sidewalk) are turned on • simultaneously as observed from the ground, based on two local clocks • synchronized on the ground. • From the point of view of the train moving with velocity v to the right, • which (if either) of the two lights turns on first? • left b) right c) simultaneously d) neither v y y' x x x’ Clicker Slide 10 Physics 2170, Fall 2014
Hubble’s data (1929) Cepheid variable stars
Riess, Press & Kirshner (1996) Type Ia supernovae
Physics Colloquium 4PM Today, Duane G1B20 Prof. Rob Schoelkopf, Yale University The Birth, Care, and Feeding of Cat States in Circuit QED: Quantum Jumps of Photon Parity
B A Particle A has half the mass but twice the speed of particle B. If the particles’ momenta are pA and pB, then a) pA > pB b) pA = pB c) pA < pB Clicker Slide 11 Physics 2170, Fall 2014
If we could release the energy of a mass entirely into energy, what mass would be needed to supply the entire world with energy each year? (Globally 4x1020J is used each year) • 1kg b) 100kg c) 5000kg d) 1,000,000kg Clicker Slide 12 Physics 2170, Fall 2014
The chemical reaction • 2H + O → H2O • is exothermic. Which weighs more, 2 hydrogen atoms and one oxygen atom (each at rest and separated), or one water molecule at rest? • they weigh the same b) H, H, O c) H2O Clicker Slide 13 Physics 2170, Fall 2014
Physics Colloquium 4PM today, Duane G1B20 Prof. Z.X. Shen, Stanford University High Temperature Superconductivity – Insights from Einstein’s Electrons
LIGO in Hanford, Washington Laser Interferometer Gravitational Wave Observatory