Choosing A as origin, E=ρj=ρ2πr21VC−VB=−2πρl∫a(a+b)r21dr=2πρl[(a+b)1−a1]VB−VC=2πρl[a1−(a+b)1]
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
Paragraph: Consider a block of conducting material of resistivity ' ρ ' shown in the figure. Current 'l' enters at 'A' and leaves from ' D '. We apply superposition principle to find voltage ' ΔV ' developed between ' B ' and ' 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) at distance ' r ' from A by using Ohm's law E=ρj, where j is the current per unit area at ' r '. (iii) From the ' r ' dependence of E(r), obtain the potential V(r) at r. (iv) Repeat (i), (ii) and (iii) for current 'l' leaving ' D ' and superpose results for ' A ' and ' D '.
Question: ΔV measured between B and C is
Held on 30 Apr 2008 · Verified 6 Jul 2026.
Options
- A
πaρl−π(a+b)ρl
- B
aρl−(a+b)ρl
- C
2πaρl−2π(a+b)ρl
- D
2π(a−b)ρl
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