A straight wire of diameter $0.5\, mm$ carrying a current of $1\, A$ is replaced by another wire of $1\, mm$ diameter carrying the same current. The strength of magnetic field far away is
A
Twice the earlier value
B
Half of the earlier value
C
Quarter of its earlier value
D
Unchanged
AIPMT 1997,AIPMT 1999, Easy
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D
Unchanged
d (d) The magnetic field is given by $B = \frac{{{\mu _0}}}{{4\pi }}\frac{{2i}}{r}$.
It is independent of the radius of the wire.
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