Question

Chapter 29, Problem 027 In the figure, two long straight wires (shown in cross section) carry currents i 23.8 mA and 12 -30.3 mA directly out of the screen. They are equal distances from the origin, where they set up a magnetic field B. To what value must current i1 be changed in order to rotate B 18.3° clockwise? Number Units the tolerance is +/-796

Answer 1

Solution)

Given ,

currents i1 = 23.8 mA and i2 = 30.3 mA

B1 and B2=fields due to the currents

B1=μoi1/2πr

B2=μoi2/2πr

hence B2/B1=i2/i1

if θ is the angle between B1 abd B2

tanθ=B2/B1

=i2/i1

=1.27

θ=51.85 deg

angle to be rotated , φ= 18.3 deg

so the net angle is δ=33.55 deg

i1 be thenew current then

i1=i2/tanδ

=45.68 mA (Ans)

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Good luck!:)