Question:

An infinitely long thin straight wire has uniform charge density of $\frac {1}{4} \times 10^{-2} cm^{-1}.$ What is the magnitude of electric field at a distance $20\, cm$ from the axis of the wire ?

Updated On: Jul 1, 2024
  • $1.12 \times 10^8 \,NC^{-1}$
  • $4.5 \times 10^8 \,NC^{-1}$
  • $2.25 \times 10^8 \,NC^{-1}$
  • $9 \times 10^8 \,NC^{-1}$
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The Correct Option is C

Solution and Explanation

We know that
$E=\frac{\lambda}{2 \pi \varepsilon_{0} r}$
$=\frac{1}{4} \times \frac{10^{-2}}{10^{-2}} \times 18 \times 10^{9} \times 5$
$=2.25 \times 10^{8} N / C$
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Concepts Used:

Electric Field

Electric Field is the electric force experienced by a unit charge. 

The electric force is calculated using the coulomb's law, whose formula is:

\(F=k\dfrac{|q_{1}q_{2}|}{r^{2}}\)

While substituting q2 as 1, electric field becomes:

 \(E=k\dfrac{|q_{1}|}{r^{2}}\)

SI unit of Electric Field is V/m (Volt per meter).