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JEE Mains · Physics · STD 12 - 4. Moving charges and magnetism

A coaxial cable consists of an inner wire of radius \('a'\) surrounded by an outer shell of inner and outer radii ' \({b}\) ' and '\(c\)' respectively. The inner wire carries an electric current is, 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 \({x}\) from the axis when \((i)\) \({x}<{a}\) and \((ii)\) \({a}<{x}<{b}\) ?

  1. A \(\frac{{x}^{2}}{{a}^{2}}\)
  2. B \(\frac{{a}^{2}}{{x}^{2}}\)
  3. C \(\frac{x^{2}}{b^{2}-a^{2}}\)
  4. D \(\frac{{b}^{2}-{a}^{2}}{{x}^{2}}\)
Verified Solution

Answer & Solution

Correct Answer

(A) \(\frac{{x}^{2}}{{a}^{2}}\)

Step-by-step Solution

Detailed explanation

when \({x}<{a}\) \({B}_{1}(2 \pi {x})=\mu_{\circ}\left(\frac{{i}_{\circ}}{\pi {a}^{2}}\right) \pi {x}^{2}\) \({B}(2 \pi {x})=\frac{\mu_{\circ} {i}_{\circ} {x}^{2}}{{a}^{2}}\) \({B}_{1}=\frac{\mu_{\circ} {i}_{\circ} {x}}{2 \pi {a}^{2}}...(1)\) when \({a}<{x}<{b}\)…
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