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Paragraph: Consider a block of conducting material of resistivity ' ρ ' shown in the figure. Current 'l' enters at 'A' and leaves from ' D '. We…

JEE Main 2008 — Physics Electromagnetism

2008mcqhard

Paragraph: Consider a block of conducting material of resistivity ' ρ\rhoρ ' shown in the figure. Current 'l' enters at 'A' and leaves from ' D\mathrm{D}D '. We apply superposition principle to find voltage ' ΔV\Delta \mathrm{V}ΔV ' developed between ' B\mathrm{B}B ' and ' C\mathrm{C}C '. The calculation is done in the following steps: (i) Take current 'l' entering from 'A' and assume it to spread over a hemispherical surface in the block. (ii) Calculate field E(r)E(r)E(r) at distance ' rrr ' from AAA by using Ohm's law E=ρjE=\rho jE=ρj, where jjj is the current per unit area at ' rrr '. (iii) From the ' rrr ' dependence of E(r)E(r)E(r), obtain the potential V(r)V(r)V(r) at rrr. (iv) Repeat (i), (ii) and (iii) for current 'l' leaving ' DDD ' and superpose results for ' AAA ' and ' DDD '.JEE Main 2008 Physics, Current Electricity — question figure

Question: ΔV\Delta \mathrm{V}ΔV measured between B\mathrm{B}B and C\mathrm{C}C is

Official previous-year question

Held on 30 Apr 2008 · Verified 6 Jul 2026.

Options

  1. A

    ρlπa−ρlπ(a+b)\frac{\rho l}{\pi a}-\frac{\rho l}{\pi(a+b)}πaρl​−π(a+b)ρl​

  2. B

    ρla−ρl(a+b)\frac{\rho l}{a}-\frac{\rho l}{(a+b)}aρl​−(a+b)ρl​

  3. C

    ρl2πa−ρl2π(a+b)\frac{\rho l}{2 \pi a}-\frac{\rho l}{2 \pi(a+b)}2πaρl​−2π(a+b)ρl​

  4. D

    ρl2π(a−b)\frac{\rho l}{2 \pi(a-b)}2π(a−b)ρl​

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