Q123 / 200 · NEET 2021 · Physics

 A thick current carrying cable of radius R carries current I uniformly distributed across its cross-section. The variation of magnetic field B(r) due to the cable with the distance r from the axis of the cable is represented by:

  • A
    Figure
  • B
    Figure
  • Correct answer
    C
    Figure
  • D
    Figure

Solution

Figure

For inside part

J=IπR2

∫B→·dl→=μ0 Iinclosed    …i

B 2πr=μ0IπR2×πr2

B 2πr=μ0Ir2R2

B∝r

For outside part

∫B→·dl→=μ0Iinclosed

B(2πr)=μ0I

∴  B∝1r

Figure

Hence, the correct answer is option: 'C'.

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