A) 2B
B) B/4
C) B/2
D) B
Correct Answer: B
Solution :
For a long straight wire, the magnetic field When \[r=5\text{ }cm\] \[B=\frac{{{\mu }_{0}}2I}{4\pi (5)}\] ...(i) Similarly, when\[r=20\text{ }cm\] \[B'=\frac{{{\mu }_{0}}2I}{4\pi (20)}\] ??.. (ii) From Eqs. (i) and (ii), we get \[B'=\frac{B}{4}\]You need to login to perform this action.
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