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A long straight wire of radius a carries a steady current I. The current is uniformlydistributed over its cross-section. The ratioof the magnetic fields B and B’, at radialdistances a/2 and 2a respectively, from theaxis of the wire is(a) 1 (6) 4 |
| Answer» B.dL=μ 0 I ENCLOSED For the smaller LOOP,⇒B×2π 2a =μ 0 × πa 2 1 ×( 2a ) 2 =μ 0 I× 41 = 4μ 0 I ⇒B 1 = 4πaμ 0 I B ′ ×2π(2a)=μ 0 IB ′ B = 4πaμ 0 I × μ 0 I4πa =1 | |