# Search results

1. ### Conceptual Problems with Random Variables and Sample Theory

Hi I'm having a few conceptual difficulties with random variables and I was hoping someone could clear up a few things for me: 1) Firstly, what exactly do we mean when we say that two random variables X and Y are equal. I understand what identically distributed means, but my difficulty is with...
2. ### The rigid rotator and Angular momentum.

If spherical harmonics are simultaneous eigenfunctions of \hat{L} and \hat{L}_{z}, then that means for a state at which l=1, and where you have three possible values of m (1, 0 , -1) that the value of L and L_{z} cannot really be determined simultaneously. Because the three fold degeneracy of...
3. ### The state of a hydrogen electon ?

The eigenstates of a hydrogen atom are stationary states with definite values of energy. Now, as I understand it, the quantum mechanical state of the electron in the hydrogen atom is really a linear superposition of all these energy eigenstates. So this should mean that there is a finite...
4. ### Special Relativity and Biological Clocks.

Hi. So the whole premise of special relativity seems to me to be hinged on the immutability of the speed of light, the fact that it is the same for every inertial frame of reference, and the fact that information and energy cannot travel faster than this. What really puzzles me is this whole...
5. ### Quasi-Mathematical Books on Various Topics in Modern Physics.

Can someone provide me with a quasi-mathematical introductory text to quantum field theory ? Ideally, a book that's somewhere between popular science and an introductory freshman physics text. I have a strong background in calculus, having just completed a one-semester equivalent reading of...
6. ### Ferromagnetism and Work done by a bar magnet.

I was just doing a read-through of my freshman griffith's electrodynamics textbook ( I found my comprehension of electrodynamics slipping again ... always gets me edgy ) and I find my self flummoxed yet again. So he goes through an example of magnetic forces lifting a weight, and shows how it's...
7. ### Scattering in Solid State Theory.

I've been reading Kittel's book on Solid state physics and while it's been mostly smooth sailing, the abrupt loss of rigour in places in unsettling. In particular, the bits about scattering seem to be just thrown in here and there without any rigourous mathematical treatment at all. He talks...
8. ### Confusion about the nature of Diffraction.

Why does the size of an obstacle have to be comparable to the wavelength of radiation for diffraction effects to be noticable ? Secondly, if the size of an opening is much smaller than the wavelength of the radiation , how does the radiation interact with the opening ? Third, can the same things...
9. ### Energy conservation in identical destructive interference.

Here's a thought experiment : Two identical spherical waves exactly 180 degrees out of phase destructively interfere throughout all of space. Is the energy contained in them just lost ?
10. ### Bound state of the delta function potential.

What is the physical meaning to a bound state with negative energy? As I understand it, this is the case with the delta function potential, which admits only one bound state with a negative energy. If the potential function is identically zero throughout (except at the delta function peak)...
11. ### Bragg's law and the distribution of electromagnetic energy.

While I get the coherent and incoherent scattering process that leads to the bragg diffraction condition, I don't really understand the physical mechanism behind the transmission and reflection. Now, as I understand it, the bragg diffraction condition is satisfied only for one or two particular...
12. ### Can't understand the algebraic theory of spin.

I've been reading Griffith's Introductory text on quantum mechanics, and I'm afraid I've hit a major roadblock. I don't understand his section on spin at all. I get the part about there being no classical analogy of quantum mechanical spin, but then he goes on to develop the algebraic theory of...
13. ### The Relativity Of Simultaneity.

Say there are two observer S and S'. Let's assume that their frames coincide at the instant t=0 and that observer S' is moving to the right at a speed 'v' with respect to the observer S along the X axis. Two lightning strikes occurs at the points A and B in the S frame at t=0. The corresponding...
14. ### Free surface of liquid.

A container filled up to about 2/3rd's with water moves with a unifrom acceleration of 'a' due to a force 'F'. Considering the fact that the defining property of a fluid requires that it's free surface be normal to the net force acting on it, how can the liquid's free surface make an angle given...
15. ### Power distribution and heaters.

This has to do with a fundamental doubt I have always had about power distribution. Say you hook up a room heater to your power supply. How exactly does the power distribution detect an increased 'load' and accordingly allot more power to your room. The way I understand it, the generating...
16. ### Car moving at constant velocity.

As I understand it, friction is the force that accelerates cars on a road. Assuming that the car moves at a constant velocity, there is no net force on the car. But in this case, if friction acts to accelerate the car, what force acts to retard the car's motion? Surely it can't be purely the...
17. ### Electric current transmitted over great distances.

Kind of a basic doubt here, but it has been nagging me for a while now. The electric field generated by a power station is a non-conservative one, and it varies as 1/r with respect to the distance of a point from the source.( I am assuming this statement is accurate.) So what I don't get is how...
18. ### Energy conservation in destructive interference.

I have followed some of the previous posts on the topic , but the conflicting arguments have left more than confused. Consider this simple scenario : Two wave pulses on a string generated by identical sources but with a phase difference of 180 degrees meet and interfere destructively. For...
19. ### Scope for pursuing physics masters in the US.

I am a second year engineering student currently enrolled in an undergrad dual degree program in BITS Pilani , India. I'm doing M.Sc (Hons.) Biology and B.E (Hons.) Chemical engineering which constitutes a 5 year long course. I am really interested in pursuing a masters degree in physics in the...
20. ### What is with the law of conservation of momentum?

Consider a scenario where someone stands on the surface of the earth and throws punches into the air. Now all the forces(which i am taking to be the tension in the muscle fibres of the arm ) acting on the system of man and earth are internal ( internal because they are exerted by one component...
21. ### Confusion about the nature of torque.

I just read another post on this website about torque and the reason for its definition as the product of the perpendicular distance of the point of application of the force from the axis of rotation and the force itself ( ignoring the vector properties of the above quantities). The explanation...
22. ### Scope for pursuing masters in physics after doing engineering.

Hey . I am a first year engineering student at BITS pilani , India. I've had this gnawing concern for a while about the scope for pursuing a masters in physics(Ideally , in the states) with a B.E in mechanical engineering(or electrical, havent decided on my engineering stream yet) and an MSC in...
23. ### Current Transmission in power lines

If the electric field at a point drops off in intensity as the inverse ratio of the square of distance from the source, how do power lines manage to carry current through such large distances?
24. ### Van Der Waal's adhesion

I have researched a little online and apparently Van Der Waal's adhesion forces play a key role in the sticky properties of glue and the bonding between gecko setae and tree surfaces. What I don't understand is why this adhesion doesn't happen between the surfaces of any two solids brought in...
25. ### Confusion with nature of induced electric field.

The whole idea of an electric field induced due to a changing magnetic flux seems to run wildly counterintuitive to me. Consider this set up as shown in my physics textbook. A current carrying solenoid placed along the axis of a circular conducting loop. A changing current through the turns of...
26. ### Confusion about the nature of magnetic forces.

Seeing as there is no net force on a magnetic dipole placed in a magnetic field ( only torque ) , and that magnetism in say a bar magnet is caused by nothing more than tiny atomic current loops ( magnetic dipoles) oriented in the same direction , i don't understand how a bar magnet would get...
27. ### Confusion with Gauss's law .

My physics textbook emphasizes that the electric field appearing in Gauss's law is the resultant electric field due to charges present both inside and outside the chosen closed surface , while the 'q' appearing in the law is only the charge contained within the surface. .This appears to follow...
28. ### Lines of force?

Do the electric lines of force necessarily depict the trajectory of a charged particle? Or do they depict the trajectory at all.
29. ### Charge on conducting and non-conducting body

the charge on a body can be distributed throughout the entire volume only if the body is non-conducting,and the charge on a conducting body can reside only on the surface. I'm confused , why?
30. ### Centripetal force .

My textbook says that the requisite centripetal force for the circular motion of a vehicle is provided by friction. I dont get that ............. i mean , shouldn't friction oppose relative motion ..........so , seeing as the direction of motion of the car is along the tangent to the curve ...