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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?