A long straight wire of radius a carries a steady current I. The current is uniformly distributed across its cross section. The ratio of the magnetic field at $\frac{a}{2}$ and $2$a from axis of the wire is:
A$1: 4$
B$4: 1$
C$1: 1$
D$3: 4$
JEE MAIN 2024, Diffcult
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C$1: 1$
c $\mathrm{B}_1 2 \pi \frac{\mathrm{a}}{2}=\mu_0 \frac{\mathrm{I}}{4}$
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