How Do You Calculate the Magnetic Field Near a Current-Carrying Ribbon?

AI Thread Summary
The discussion focuses on calculating the magnetic field near a current-carrying ribbon, specifically at a distance of 2.16 cm from its edge. The initial calculations using the Biot-Savart law yielded results that did not match the expected answer of 22.3 pT. Participants questioned the methodology, particularly the relevance of subtracting two different magnetic field values and whether the calculation was for a point outside the ribbon. Ultimately, the original poster resolved the issue but did not share the solution. The thread highlights the importance of clarity in calculations and understanding the context of the problem.
Amy Marie
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Homework Statement


Figure 29-61 shows a cross section of a long thin ribbon of width w = 4.91 cm that is carrying a uniformly distributed total current i = 4.61 * 10^-6 A into the page. What is the magnetic field at a point in the plane of the ribbon at a distance 2.16 cm from its edge?

Homework Equations


B = ((1.26 * 10^-6)i)/(2*pi*R)

The Attempt at a Solution


I tried using the Biot-Savart law:

0.0491 m + 0.0216 m = 0.0707 m

((1.26 * 10^-6)(4.61 * 10^-6))/(2*pi*0.0707) = 1.3 * 10^-11 T

((1.26* 10^-6)(4.61 * 10^-6))/(2*pi*0.0216) = 4.28 * 10^-11 T

(4.28 * 10^-11) - (1.3 * 10^-11) = 2.98 * 10^-11 T

When I checked, the answer was 22.3 pT instead of 29.8 pT.
Can anybody please let me know what I should be doing differently?
 
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I don't understand your calculations.
Amy Marie said:
((1.26 * 10^-6)(4.61 * 10^-6))/(2*pi*0.0707) = 1.3 * 10^-11 T
This is the field 2.16cm outside, okay. The units are missing.
Amy Marie said:
((1.26* 10^-6)(4.61 * 10^-6))/(2*pi*0.0216) = 4.28 * 10^-11 T
What is this?
And where is the point in subtracting the two values?

Does the question really ask for a point outside? That would make the details about the ribbon pointless.
 
mfb said:
I don't understand your calculations.This is the field 2.16cm outside, okay. The units are missing.
What is this?
And where is the point in subtracting the two values?

Does the question really ask for a point outside? That would make the details about the ribbon pointless.
I figured the problem out, but thank you.
 
Amy Marie said:
I figured the problem out, but thank you.
how did you solve it
using what equation
 
This thread is from 2014 and OP didn't post anything in this forum in the last three years, it is unlikely that you will get an answer.
 
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