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JEE Main 202127 AugustEvening Shift
Exam
JEE Main
Year
2021
Date
27 August
Shift
Evening Shift
Subject
Physics
Chapter
Magnetic Effects of Current

JEE Main 2021 · 27 August · Evening Shift · Physics · Magnetic Effects of Current

A coaxial cable consists of an inner wire of radius a surrounded by...

A coaxial cable consists of an inner wire of radius aa surrounded by an outer shell of inner and outer radii bandcb and c respectively. The inner wire carries an electric current i0{i}_{0} which is distributed uniformly across cross-sectional area. The outer shell carries an equal current in opposite direction and distributed uniformly. What will be the ratio of the magnetic field at a distance xx from the axis when \left(i\right) x < a and \left(ii\right) a < x < b$ ?

Options

  1. Aa2x2\dfrac{{a}^{2}}{{x}^{2}}
  2. Bb2−a2x2\dfrac{{b}^{2} - {a}^{2}}{{x}^{2}}
  3. Cx2b2−a2\dfrac{{x}^{2}}{{b}^{2} - {a}^{2}}
  4. Dx2a2\dfrac{{x}^{2}}{{a}^{2}}

Correct answer

D. x2a2\dfrac{{x}^{2}}{{a}^{2}}

Step-by-step solution

B1×2\pix=μ0I0(x)2a2{B}_{1} \times 2\pix = \dfrac{{\mu}_{0}{I}_{0} ( x{)}^{2}}{{a}^{2}}

B2×2\pix=μ0I0{B}_{2} \times 2\pix = {\mu}_{0}{I}_{0}

B1B2=x2a2\dfrac{{B}_{1}}{{B}_{2}} = \dfrac{{x}^{2}}{{a}^{2}}

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