Physics

Two fixed, non-conductive, isolated rings of radii 25 cm are electrified and brought close to each other so that they are parallel. The distance between them is 1 m. You know that one of them has a charge of 1 nC(Nano Coulomb) evenly distributed on it, but you are not sure about the other. In order to find out what's the charge on the other, you take a charged ball and move it across the axis of the rings until you find its equilibrium position. You measure where that is and get that the equilibrium position is 25 cm from the ring with the known charge. What's the charge in nC of the second ring?
Details and assumptions:
The second ring also has evenly distributed positive charge on it.

  1. 👍 0
  2. 👎 0
  3. 👁 62
  1. I solved it like this
    let charge of the ball be Q
    let charge of unkown ring be Q2
    let the place where there is equilbrium be
    P. This point P is 0.25m from the ring with known charge and and hence 0.75m from the ring with unknown charge.
    Now applying coulomb's law at this point P from both the rings and this force must be equal as the point is in chrge equilibrim.
    So at point p
    (k*Q2*Q)/(0.75)^2 = (k*1*10^-9*Q)/(0.25)^2
    [As known charge is 1nC)
    Solving we get Q2 = 9 nC.
    But the answer is incorrect so what should be the correct answer ?
    PLEASE HELP !

    1. 👍 0
    2. 👎 0
  2. Electric field on the axis of the ring at the distance ‘x’ from the center of it is
    E = k xq/{sqrt(R²+x²)}³
    k=1/4πε₀
    The test charge is in equilibrium =>
    E₁=E₂
    k x₁q₁/{sqrt(R²+x₁²)}³=
    =k x₂q₂/{sqrt(R²+x₂²)}³,

    q= x₁q₁{sqrt(R²+x₂²)}³/{sqrt(R²+x₁²)}³=
    =0.25•1•10⁻⁹•{sqrt(0.25²+0.75²)}³/{sqrt(0.25²+0.25²)}³=
    =2.8•10⁻⁹ C = 2.9 nC

    1. 👍 0
    2. 👎 0
    posted by Elena
  3. Hey elena but why is my method wrong ?

    1. 👍 0
    2. 👎 0
  4. wait 2.8 and 2.9 are both wrong.

    1. 👍 0
    2. 👎 0
    posted by idk
  5. Physics Lover : The Coulomb formula is only valid for a point, not a ring

    1. 👍 0
    2. 👎 0
    posted by finnt
  6. Yeah the answer is wrong so what should be correct ?

    1. 👍 0
    2. 👎 0
  7. 3.73 is the perfect answer. Elena has done it right, but has made some mistake in calculation

    1. 👍 0
    2. 👎 0

Respond to this Question

First Name

Your Response

Similar Questions

  1. physics

    Two identical superconducting rings are brought very close to each other (see the image below). The currents in the rings are equal to I,=0.05 A. Determine the the current I in Amps in the rings if we separate them far apart.

    asked by er on April 25, 2013
  2. Physics

    Three concentric rings and one point charge are in the same plane as shown in the above diagram. The linear charge densities of the rings are ë1 = 2.60nC/m, ë2 = -1.10nC/m, and ë3 = 2.20nC/m with corresponding radii of r1 =

    asked by Nick on January 17, 2013
  3. Statistics

    On the fifth day of Statistics, my teacher gave to me….five golden rings. The rings from which she could select were: 10 golden rings, 5 silver rings and 3 platinum rings. Knowing that your Statistics teacher would naturally

    asked by Please Help on December 25, 2015
  4. Pre Algebra

    A customer at the ring toss booth gets eight rings for two dollars find the constant of proportionality and write an equation relating the cost to the number of rings. At the same rate how much would a customer pay for 11 rings?

    asked by Stephany on January 20, 2016
  5. physics

    Two rings of radius 3 cm are 23 cm apart and concentric with a common horizontal x-axis. What is the magnitude of the electric field midway between the rings if both rings carry a charge of +35 nC?

    asked by Ali on February 4, 2016
  6. english

    in the book Beowulf what are "the rings" whick are spoken of in the prologue I may be missing something here. The only rings I remember in the prologue is the "Breaker-of-rings"...an important person, or chiefian, whose job it is

    asked by Keisha on August 28, 2005
  7. Anatomy And Physiology

    A 63 year old man has become progressively hard of hearing. He's a retired airplane mechanic. He also notices a lot of wax in his ears. What kind of hearing loss is this man likely to have? A. conductive B. conductive AND

    asked by Bailey on February 21, 2009
  8. Anatomy and Physiology

    A 63-year-old man has become progressively hard of hearing. He's a retired airplane mechanic. He also notices a lot of wax in his ears. What kind of hearing loss is this man likely to have? A. Conductive B. Conductive AND

    asked by Bailey on February 21, 2009
  9. science help

    One group of students is investigating the properties of charged objects. Their observations are listed below. When two positively charged objects are brought close to each other, they push each other away. When two negatively

    asked by Oscar on December 1, 2015
  10. math

    complete the table that shows the length of the chain formed when rings are liked in a staright line 1)number of rings 1 length of chain 16mm 2)number of rings 2 length of chain 30m 3)number of rings 3 length of chain 44m 4)number

    asked by marcus on May 19, 2008

More Similar Questions