Browse by Stream
QnA
Home
QnA
Go To Your Study Dashboard

Get Answers to all your Questions

header-bg qa

For current entering at A, the electric field at a distance r  from A  is 

 

Directions : Consider a block of conducting material of resistivity  \rho shown in the figure. Current I enters at A    and leaves from  D  . We apply superposition principle to find voltage \Delta V developed between  B and C The calculation is done in the following steps:

(i)    Take current  I   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=\rho j  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  I leaving D and superpose results for A and B

 

  • Option 1)

    \frac{\rho I}{4\pi r^{2}}

  • Option 2)

    \frac{\rho I}{8\pi r^{2}}

  • Option 3)

    \frac{\rho I}{ r^{2}}

  • Option 4)

    \frac{\rho I}{2\pi r^{2}}

 

Answers (1)

best_answer

As we learnt in 

If current density is uniform -

\vec{J}=\frac{\vec{I}}{A}

- wherein

\vec{J-} Current density

\vec{A-} Normal cross-section

 

 

Current density, j= \frac{I}{2\pi r^{2}}'

Resistance= \frac{\rho I}{area}= \frac{\rho r}{2\pi r^{2}}

E= \frac{I\rho }{2\pi r^{2}}


Option 1)

\frac{\rho I}{4\pi r^{2}}

This option is incorrect.

Option 2)

\frac{\rho I}{8\pi r^{2}}

This option is incorrect.

Option 3)

\frac{\rho I}{ r^{2}}

This option is incorrect.

Option 4)

\frac{\rho I}{2\pi r^{2}}

This option is correct.

Posted by

Plabita

View full answer

JEE Main high-scoring chapters and topics

Study 40% syllabus and score up to 100% marks in JEE

Similar Questions

Trending Articles/News

anam-khan

JEE Main 2024 Topper: Farmer’s son Gajare Nilkrishna says ‘keep questioning until you understand’
anam-khan

NIT Puducherry Cut-off 2024: Computer Science and Engineering had highest closing rank last year
anam-khan

JEE Mains: Farmer's son from remote Maharashtra village aces exam

Latest Question