The 1st, 2nd and 3rd quadrants of the Cartesian Coordinate plane are given a charge density 1C/m^2.

What work has to be done in taking a unit positive charge from z=1 to z=3?

21 comments:

  1. 3(epsilon)/4

    i have seen this earlier
    but im myself not convinced how we can treat infinite plate like this

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  2. @sambhav: i guess u mean 3/(4(epsilon0)

    as for your doubt.. for calculating the work here, we need only the z component of the electric field.. thus done!

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  3. how are we applying infinite plate formula?

    wasn't that formula meant for a point symmetrically placed close to somewhat the center of a really, really large plate?

    yahan to vo point corner par placed hai?

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  4. no yaar, its not that. what actually is happening is that we have taken that whole cartesian is an infinite plane. now obviously charge density would remain same. then, apply formula sigma/2(epsilon). now actually we dont have 4th quadrant so, net is by 3only. by symmetry contribution is equal. therefore, 3/4.

    I hope it is clear now!

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  5. amit u r incomplete..

    see guys obviously the z component of field contributed by d 3 quadrants will be the same.. direction as well as magnitude..

    the difference in direction will be there only for the x-y plane component of the field..

    now for the work.. ie, qV we integrate E.dr.. but dr=dz k cap.. hence we need only the z component of the field!

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  6. yaar plz help with this one..

    http://anujkalia.blogspot.com/2010/12/i-love-this-one.html

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  7. shivanker, what's E in your solution

    and i myself am waiting for anuj bhaiya on that

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  8. shivanker, acc. to your soln you will take E each of quadrant and net you will get 3E. from where will you get 4 in denominator.

    I have replied to love this one post

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  9. every quadrant will contribute sigma/(8.epsilon0) in +z direction..

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  10. @sambhav.. E as used by me in that post is simply any electric field existing in that region.. but actually it doesn't matter.. what matters is the Z-component of the field E..

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  11. shivanker main bhi to yahi keh raha hun ki every field will contribute sigma/8(epsilon)

    answer is -(3/4(epsilon))

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  12. HI
    someone please help me in this question, i have been trying this for over 2 hours.

    A PARTICLE MOVES WITH A CONSTANT SPEED 1.5 m/s ALONG A PATH GIVEN BY x=y^2 - ln(y). GIVE THE ACCELERATION OF THE PARTICLE IN VECTOR FORM AT THE POSITION Y=3m.

    answer given is -.225i +4.5j (or i,j cud be reveresed, its just given in component form in the answer)

    thaks in advance.....!!!

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  14. @ blog admin
    answer is 3/4(epsilon)
    i verified this analogy by assuming plane to be 3 quarters of charged ring and then integrating for a disc.
    Result was same.

    @ delhietie

    bro this answer must be wrong
    i tried a lil hook n crook but the vector sum of velocities deduced by this acceleration would never sum up to 1.5
    and
    acceleration in x direction must not be negative, instead in y direction must be negative as the particle bends towards x axis rapidly.

    i got this answer a = 2.111 i - 0.372 j

    my steps were
    1) differentiate twice and put value 3
    2) this acceleration will be directed in direction of motion at that instant.
    3) Take components acos@ and a sin@
    4) find out tan@ = slope on tangent at that point by differentiating one time.
    5) Find sin@ and cos@ from tan@
    6) find acos@ + asin@

    But i cant assure you of its correctness
    took me a day but could not cross examine it.

    where did u find this question ??

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  15. hi Shivam.t aka shiveminem

    thanks a lot man for giving your time!!

    (yaar, that was a dash in front of .225, not a minus)
    see i think your step 2] is wrong(it is given velocity is constant)

    i am mainly having a problem in bringing the answer into vector form.
    some one please help

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  16. @delhiite, I didn't solve your question but I know how to do it. I will give you the method.
    diff given equation wrt time.
    dx/dt=vx
    dy/dt=vy
    vx^2+vy^2=v^2 i.e constant.

    now find vx in terms of v and x
    vy in terms of v and y. Now again diff to get equation in ax.
    I am just telling you the way. You have to solve yourself, you will get the answer

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  17. The answer to the question posted by me is sigma/4(epsilon0);

    Hint: remember how you calculated the radial component of the field due to a semi-infinite wire.

    The solution to the question asked by delhite is as follows:

    1)Calculate the radius of curvature of the path at y=3. (I assume you know the formula).

    2)Get the direction cosines of the normal i.e (-dx/dy).

    3)Accn. is in the direction of the normal vector and is v^2/r in magnitude.

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  18. @anuj bhaiya:

    bhaiya usi method se kiya tha..
    vertical component of the field will be 3/4*sigma/2(epsilon0)

    so answer is 3sigma/4(epsilon0)

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