A)
B)
C)
D)
Correct Answer: B
Solution :
When a current flows through cylindrical shell, then according to Ampere circuital law, magnetic induction inside it will be equal to zero. Hence energy density at \[r<R\] is equal to zero. Therefore, (a), (c) and (d) are wrong. When r > R, \[B=\frac{{{\mu }_{0}}i}{2\pi r}\]. Since \[U=\frac{{{B}^{2}}}{2{{\mu }_{0}}},\]therefore, outside the shell, \[U=\frac{{{\mu }_{0}}{{i}^{2}}}{8{{\pi }^{2}}{{r}^{2}}}\]. It means, just outside the shell, \[U=\frac{{{\mu }_{0}}{{i}^{2}}}{8{{\pi }^{2}}{{R}^{2}}}\]and when \[r\to \infty ,\ U\to 0.\] Hence (b) is correct.
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