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Dipole in a nonuniform electric field problem

  • Thread starter BrainMan
  • Start date
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1. Homework Statement
A point charge Q is held at a distance r from the center of a dipole that consists of two charges ±q separated by a distance s. The dipole is initially oriented so that Q is in the plane bisecting the dipole. Assume that r≫s.

A) Immediately after the dipole is released, what is the magnitude of the force on the dipole?

B) Immediately after the dipole is released, what is the magnitude of the torque on the dipole?

2. Homework Equations


3. The Attempt at a Solution
[PLAIN]https://lh3.googleusercontent.com/krQ_JEzmRURs4ZqAkRwrapePDCVyz9DBcELyMJ8-tY1g2JYfSLGdkD4lv4_F_2FaaeXrNoN-ZofGqnvD3VNp8AgsogPnk_kYrS2RL9SY5A6K-q9RTfBwq5_Nv_exlvGk5w_Ui0p2kXAdQa1Jw005jR1eRS9G-0lFjnzhD7CfsHB8-pmm0Kxj-BRM_MQbHapBvyIVizorUYPVqCZNcPo1I8I0u83mzPTSJJdylwMoiC2qDsochCphoyNwRT62P_0p_VF0SKk2qpIhhLIdGO9EUow30nxJjp4EvvSKOMZGSaHl-aXsbewtiwn9ky2DmswaV_GOlaW2UFAhDKbytrYhK9GJ-kyP_PLobfQ_jyhIkKldBX29OF8DUKXyodk6Q4n3N5aW1X10msWQ_tzuchKdsmubrePdPNWxTWIHfLr4z9PL4NeXi5BaCm7QSaWWAyAWmRTkJwUx7AE9zwLyqdBmrwSxZIgZlK2z5_LM8rlKqCK3XdixKgaDBS9tOzi4wLe9Gp96Jn7gJpG_m5EwwgaA3LVHTWIWAWFvqzb_FXTW86j-81g_mAdb2Xltz2xyBYoA_Ozaai1Q46fI5-cPOp7f_rezMCPQ5gmLG-jD6g6m-KSyFMMzCkuT=w497-h662-no[/B] [Broken]

I treated the two charges on the dipole as point charges and then found the force vectors acting on them. Then I broke down the forces into their components and added them. The x components canceled and I was left with just a y component. For some reason this is wrong, though.
 
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kuruman

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It is not easy to read what the y-component is. Can you use LaTeX to write it down? I agree that the x-component is zero.
 
279
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It is not easy to read what the y-component is. Can you use LaTeX to write it down? I agree that the x-component is zero.
Here is the net y-component of the force.

[tex] \frac{Qqs}{4\pi\epsilon_{0}(r^2+\frac{s^2}{4})^{3/2}} [/tex]
 

gneill

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I suspect that they want you to incorporate their specified assumption: Assume that r≫s
 

kuruman

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I suspect that they want you to incorporate their specified assumption: Assume that r≫s
Exactly what I was about to type in. Before you do that, factor out of the radical r in the denominator.
 

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