According to Gauss’s law, the electric field due to an infinitely long thin charged wire varies as:

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  1. 1/r
  2. 1/r2
  3. r
  4. r2

Answer (Detailed Solution Below)

Option 1 : 1/r
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CONCEPT:

Gauss’s Law: Total electric flux through a closed surface is 1/εo times the charge enclosed in the surface i.e. \({\rm{\Phi }} = \frac{q}{{{\epsilon_o}}}\)

But we know that Electrical flux through a closed surface is \(\oint \vec E \cdot \overrightarrow {ds} \)

\(\therefore\oint \vec E \cdot \overrightarrow {ds} = \frac{q}{{{\epsilon_o}}}\)

Where, E = electric field, q = charge enclosed in the surface and εo = permittivity of free space.

EXPLANATION:

Electric field due to line charge:

F1 P.Y Madhu 16.04.20 D5 1

Electric field due to an infinitely long straight conductor is 

\(E=\frac{\lambda }{2\pi {{\epsilon }_{o}}r}~\)

Where λ = linear charge density, r = radius of the cylinder, and εo = permittivity of free space.

From the above equation, it is clear that the electric field of an infinitely long straight wire is proportional to 1/r. Hence option 1 is correct.

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