Q 12-01-016NEETJEE MainEasy
The electric field at a distance $r$ from an infinitely long straight wire with uniform linear charge density $\lambda$ is
Answer: (D) $\dfrac{\lambda}{2\pi\epsilon_0 r}$
Concept. Gauss's law with a coaxial cylinder of radius $r$ and length $L$.
Step 1. Apply.
$$E(2\pi rL) = \frac{\lambda L}{\epsilon_0} \;\Rightarrow\; E = \frac{\lambda}{2\pi\epsilon_0r}$$
Answer. $\dfrac{\lambda}{2\pi\epsilon_0r}$ (Option D).
Solution by Sreeraj P, M.Sc Physics