some questions..

Discussion in 'Physics & Math' started by rohIT, Jan 17, 2013.

  1. rohIT Registered Senior Member

    Messages:
    76
    so, i have these small doubts of sorts...
    so, was hopin to get em cleared over here!

    1 why is pressure considered to be low at areas where velocity is more? (Bernoulli theorem)

    2 when only one plate of a charged condenser is connected to ground, is nothing supposed to happen to the total charge on the capacitor?

    3 in solid and hollow cylindrical conductors, please tell me how the magnetic and electric fields vary inside the conductor.

    4 okay, there is this weird thing in one of my books which says that for uranium, mass varies inversely with volume. what could that possibly mean?

    5 why does the plane of rotation (does this mean the plane of the orbit?) of a satellite have to pass through the center of the planet it revolves around? (and is it necessary that its orbit passes through the centre of the planet too? and, of course, why?)

    6 another thing written in my book says electron capture occurs more often than positron emission in heavy elements because, well, it says that if positron emission is energetically allowed, then electron capture is necessarily allowed. n i dont know what it means

    Please Register or Log in to view the hidden image!



    7 please tell me what happens when a wave pulse is incident from a thin (or thick) string onto a thick (or thin) string and why.

    8 electric field at any point inside or outside a given gaussian surface is contributed by all the charges that are present irrespective of whether they are present inside or outside it. am i right at this?

    9 how does electric dipole moment vary with dielectric constant of the medium n y?

    yep, that will be all for now...
    please reply to these asap.
    thanks in advance

    Please Register or Log in to view the hidden image!

     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. eram Sciengineer Valued Senior Member

    Messages:
    1,877
    1. Conservation of energy

    \(\frac{mu^{2}}{2}+pV=c\)

    V = volume, u = velocity, p = pressure

    So when the velocity goes up, the pressure may fall.



    2. Nope, the charge will leak away.


    3. If the conductive material is ferromagnetic, the magnetic field will be "concentrated" within the material. So within the hollow cylinder, there'll be no magnetic field. The electric field strength in both cases is effectively zero.


    4. I have no idea.


    5. The plane of orbit of a satellite has to pass through the center of the planet it revolves around. For a spherical mass, the gravitational field lines all point towards the spherical center. If the satellite was orbiting off-center, it would require another force to balance a component of the planet's gravitational attraction to remain in orbit. As for the 2nd part, I haven't heard of satellites passing through a planet, have you?


    6. The amount of energy converted during positron emission is always less than the amount of energy converted during electron capture. Hence, if positron emission is thermodynamically feasible (resulting in a net release of energy), so is electron capture, but not vice versa.


    7. From thin to thick, the wave encounters a more resistive boundary condition and there will be a significant phase change. From thick to thin, no phase change.


    8. Yes.


    9. http://en.wikipedia.org/wiki/Electr...ric_sphere_in_uniform_external_electric_field
     
    Last edited: Jan 17, 2013
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,222
    #5: Objects are attracted to the center of gravity of other massive objects, and the geometric center of planets typically corresponds with their center of gravity. This necessitates that an orbiting object make a plane through this CoG point.
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. rohIT Registered Senior Member

    Messages:
    76
    wow guys, thanks a ton!
    now i know where i am gettin my doubts cleared

    Please Register or Log in to view the hidden image!

     
  8. James R Just this guy, you know? Staff Member

    Messages:
    39,397
    Apologies in advance for duplication.

    Because to speed a fluid up you need to apply a larger force on one end than the other. The end with the smaller force will have a higher velocity, and the fluid will flow in the direction from large force to small.

    Yes. Nothing happens unless the other plate is connected to something.

    The electric field inside either conductor is zero. The magnetic field only exists if a current flows along the surface, and in that case the field inside is approximately constant for a hollow conductor. For a solid conductor carrying a current, I think the magnetic field goes linearly as the distance from the axis.

    Without context, there's no way to tell.

    eram already explained this.

    Again, eram explained it.

    And again...

    Yes. The net electric flux through the surface, on the other hand, is a different matter.

    It doesn't.
     
  9. Crunchy Cat F-in' *meow* baby!!! Valued Senior Member

    Messages:
    8,423
    It sounds more like you are asking people to do your homework.
     
  10. rohIT Registered Senior Member

    Messages:
    76
    lol, its not my homework, im just tryin to answer some question books n sometimes, i dont understand stuff.
    n thanks!
     
  11. rohIT Registered Senior Member

    Messages:
    76
    when u say this, shouldnt the velocity be uniform and the net force considered, considering liquids (as was the case in the question) are incompressible?

    when any charged body is connected to earth, the charge drops to 0. and in one of the questions which involved a shell inside another shell (both being charged) and the inner shell bein connected to ground, the charge fell until its potential became 0. why is it different in case of condensers? why wont the potential become 0?

    consider this. because dipole moment is defined as the product of charge and distance between the charges and because the effective distance increases when a dielectric is introduced, shouldnt the dipole moment increase?
     
  12. eram Sciengineer Valued Senior Member

    Messages:
    1,877
    as seen in the wiki, for a dielectric sphere in uniform external electric field the electric dipole moment decreases with increasing dielectric constant
     
  13. James R Just this guy, you know? Staff Member

    Messages:
    39,397
    rohIT:

    Bernoulli's equation applies to flowstreams in an incompressible fluid. If the area of the stream changes (e.g. a fluid in a pipe goes from a large area to a smaller area) then the fluid must change speed due to its incompressibility.

    No, that's not right. If there's another charged object nearby then the object connected to Earth won't discharge. It may, in fact, charge when it had no charge originally.

    Potential is not the same thing as charge. Ground is usually defined to be zero potential, so any conductor connected to it (charged or not) must be at zero potential by definition. But only potential differences have any impact on what currents flow and so on.

    What is this "effective distance" thing, and why would it change? What kind of dipole are you talking about?


    eram:

    What is a dielectric sphere? Is that the same as a basic electric dipole?
     

Share This Page