Recent content by AlonsoMcLaren

I hate Olympiad problems. That's why I am a physics major now. You do need some "trick" aspect as found in Olympiad problems to succeed as a math major. Just check how many Fields Medialists were former Olympiad national team members... But unfortunately I am very brute force when it comes to...

A really basic question: since room temperature (300K) is much lower than the Curie point of iron (1043K), the spins in an iron bar at room temperature should be lined up even when the external magnetic field B=0 Then why can't we use any iron bar as magnet? Instead we have to rub the iron bar...

I have not heard of any "law of conservation of translational kinetic energy"... So in Problem (B), the balls are rolling without slipping immediately after collision, not the case in Problem (A)? How do I even know about that? Therefore knowing the velocities, masses and momenta of inertia of...

Homework Statement There are two problems: (A) Consider two identical billiard balls (spheres), each of mass M and radius R. One is stationary (ball 2) and the other rolls on a horizontal surface without slipping, with a horizontal speed v (ball 1). Assume that all the frictional forces are...

Yes I do mean the physical reasons behind these rules

While I am reviewing my undergrad physics for qualifying exam, I became confused about the numerous selection rules. (1) We have the selection rules for spontaneous emission in a hydrogen atom: Δl=±1 ,Δml=0,±1. This rule is the easiest to understand by evaluating <n'l'm'|z|nlm> (2) We have the...

So basically in a noninertial frame, Maxwell's equations do not hold (Otherwise there should be no magnetic field in the rotating frame because there is no current source)? Also, for the exam problem, why E=0 inside the metal sphere at the origin of the co-moving inertial frame (call it P)...

Homework Statement http://physics.columbia.edu/files/physics/content/Quals2010Sec2.pdf Problem 1 Consider a rigid, ideally conducting sphere of radius R, with total charge zero. The sphere rotates with angular velocity Ω, ΩR<<c. Suppose a dipole magnetic field threads the sphere. the dipole is...

On "six ideas that shaped physics" p.43 the author says "The observer in the Home Frame (ground) will agree that the right and left clocks in the Other Frame (train) are always equidistant from the center clock in the Other Frame," I don't understand why. Are we in a position to be sure about...

In the train example that supposedly shows the relativity of simultaneity, why, in the frame of the observer on the ground, the "midpoint" of the train in the train's frame is still the midpoint? Does it have anything to do with Lorentz contraction? If so, there might be some circular reasoning...

We know that in Cartesian position basis the representation of momentum is -ihbar (d/dx) Consider a cylindrical/spherical/whatever curvilinear coordinates. To make life simple, consider a particle constrained to move on a circle so that its position can described by θ only. Suppose we express...

So why energy has different types and momentum does not?

I am reading Landau's mechanics. He proved that energy and momentum are conserved in an isolated system when we forget about non conservative systems. But why is energy not conserved in non conservative system, but momentum is? What is the proof? I know we can show that momentum conservation...

Is π|spin up>=|spin down>?, where π is the parity operator. I can't find a definitive answer from Sakurai.

1. Are uncountable unions of sigma algebras on a set X still a sigma algebra on X? 2. Are uncountable intersections of sigma algebras on a set X still a sigma algebra on X? (I think this statement is required to show the existence of sigma algebra generated by a set) 3. If 2 is true, can we...