NEET-XII-Physics
exam-1 year:2016
- #26A long straight wire of radius a carries a steady
current I. The current is uniformly distributed over
its cross-section. The ratio of the magnetic fields
B and B', at radial distances a/2 and 2a respectively,
from the axis of the wire is :
(1)``\frac {1}{4}``
(2)``\frac {1}{2}``
(3) 1
(4) 4digAnsr: 3Ans : 3
Sol. For points inside the wire
=
0
2
µ Ir
B (r R)
2 R
For points outside the wire
= ≥
0µ IB (r R)
2 r
according to the question
=
0
2
0
I(a / 2)
B 2 a
IB '
2 (2a)
= 1 : 1