Published by:
CGP EDU Academic Team
Published on: August 13, 2026
A long straight wire of circular cross-section (radius a) carries a steady current 
. The current is uniformly distributed over the cross-section. Which of the plots of magnetic field magnitude 
versus distancer rom the centre of the wire is correct?
A
increases linearly from 
to 
, reaches a maximum at 
, then falls off for 
like 
. B
is constant from 
to 
, then falls off for 
. ' C
is zero up to 
then jumps and decays for 
. D
is maximum at the centre and decreases monotonically with 
.
Text Solution
Verified by ExpertsThe correct answer is:
A
.
So 
(linear increase from 
to 
).
,
i.e. 
falls off as 
.
At 
.
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