https://imgur.com/czrfm33 The figure represents a cross-section through two conc
ID: 1517233 • Letter: H
Question
https://imgur.com/czrfm33
The figure represents a cross-section through two concentric cylindrical conductors. The first has radius a and is inside of the larger conductor of radius b. The inner conductor has current +I running into the page and the outer conductor carried a current of -2I out of the page.
Give an expression for the magnetic field at all points outside the outer conductor specifying direction.
The magnetic field at r=0 and r=infinity is zero. Give another distance r from the center of the circle at which the magnetic field is also zero.
Explanation / Answer
a) By amperes law
B.2pi r = uo ienclosed
B = uo (2i-i)/ (2 pi r)
= uo i/2 pi r counterclockwise
B) magnetic field will be zero at r where i enclosed is zero
pi (b^2 - a^2) =2* pi ( r^2 - a^2)
b^2 - a^2 = 2 r^2 -2a^2
r = sqrt (( b^2 + a^2)/2)
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