Magnitude of electric field 32m from a rod

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SUMMARY

The discussion centers on calculating the electric field produced by a uniformly charged rod, specifically a 55cm long rod with a 4.4μC charge. The electric field magnitude was correctly calculated at 4.0mm from the rod surface as 1.0 x 107 N/C using the formula E = q_enclosed/(2∏*ε0*r*L). However, the calculated electric field at 32m was incorrectly determined to be 4.5 x 103 N/C, indicating a misunderstanding of the far-field approximation and the distribution of charge at greater distances.

PREREQUISITES
  • Understanding of electric fields and Coulomb's law
  • Familiarity with the formula E = q_enclosed/(2∏*ε0*r*L)
  • Knowledge of the concept of charge distribution along a rod
  • Basic principles of electrostatics and field calculations
NEXT STEPS
  • Review the concept of electric field approximation in electrostatics
  • Study the effects of distance on electric field strength
  • Learn about the significance of charge distribution in calculating electric fields
  • Explore the differences between near-field and far-field calculations in electrostatics
USEFUL FOR

Students studying electrostatics, physics educators, and anyone interested in understanding electric field calculations related to charged objects.

Les talons
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Homework Statement


"A rod 55cm long and 1.0cm in radius carries a 4.4μC charge distributed uniformly over its length. What is the approximate magnitude of the electric field 4.0mm from the rod surface, not near either end? What is the approximate magnitude of the electric field 32m from the rod?"

Homework Equations


E = q_enclosed/(2∏*ε_0*r*L)


The Attempt at a Solution


For the field at 4.0mm, I calculated the magnitude as: (4.4/1*10^6)N/(2∏*8.85*10^(-12)*0.014*0.55)C = 1.0*10^7 N/C
For the field at 32m, I calculated it the same way: (4.4/1*10^6)N/(2∏*8.85*10^(-12)*32.01*0.55)C = 4.5*10^3 N/C
The answer for the field I got at 4.0mm is correct, but the magnitude found at 32m is wrong. I don't see how the formula for the magnitude would change in the two situations. The change in magnitude looks good to me since the distance from the rod increases by a factor of 10^3. There is still not any flux through the ends of the rod, so that would not change the calculation, either. I must be missing something really obvious. Thanks for reading!
 
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The difference is between close up and a long way away.
Did you use an approximation in the near-field calculation?
Are you expected to use one in the far-field calculation?

What makes you think there is no flux through the ends of the rod?
 
At 32 m each part of the rod is approximately equidistant from every other part of the rod, in a percentage sense. Use that fact.
 
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