A) 25
B) B/4
C) B/2
D) B
Correct Answer: B
Solution :
For a long straight wire, the magnetic field \[B=\frac{{{\mu }_{0}}2I}{4\pi r}\] When \[r=5\text{ }cm\] \[\therefore \] \[B=\frac{{{\mu }_{0}}2I}{4\pi (5)}\] ?.(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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