Question
  1. Show that the normal component of electrostatic field has a discontinuity from one side of a charged surface to another given by
$(\text{E}_2-\text{E}_1).\hat{\text{n}}=\frac{\sigma}{\epsilon_0}$
where $\hat{\text{n}}$ is a unit vector normal to the surface at a point and $\sigma$ is the surface charge density at that point. $ ($The direction of $\hat{\text{n}}$ is from side $1$ to side $2.)$ Hence show that just outside a conductor, the electric field is $\sigma \hat{\text{n}} /ε_0.$
  1. Show that the tangential component of electrostatic field is continuous from one side of a charged surface to another.
$[$Hint: For $(a),$ use Gauss’s law. For $, (b)$ use the fact that work done by electrostatic field on a closed loop is zero.$]$

Answer

  1. Electric fielcl on one side of a charged body is $E_1$ and electric field on the other side of the same body is $E_2$. If infinite plane charged body has a uniform thickness, then electric field due to one surface of the charged body is given by,
  1. $\vec{\text{E}}_1=-\frac{\sigma}{2\in_0}\hat{\text{n}} \dots\dots(1)$
    Where,
    $\hat{\text{n}} =$ Unit vector normal to the surface at a point
    $\sigma = $ Surface charge density at that point
    Electric field due to the other surface of the charged body,
    $\vec{\text{E}}_2=-\frac{\sigma}{2\in_0}\hat{\text{n}} \dots\dots(2)$
    Electric field at any point due to the two surfaces,
    $\vec{\text{E}}_2-\vec{\text{E}}_1=\frac{\sigma}{2\in_0}\hat{\text{n}}+\frac{\sigma}{2\in_0}\hat{\text{n}}=\frac{\sigma}{\in_0}\hat{\text{n}}$
    $(\vec{\text{E}}_2-\vec{\text{E}}_1).\hat{\text{n}}=\frac{\sigma}{\in_0} \dots\dots(3)$
    Since inside a closed conductor, $\vec{\text{E}}_1=0,$
    $\therefore\vec{\text{E}}=\vec{\text{E}}_2=-\frac{\sigma}{2\in_0}\hat{\text{n}}$
    Therefore, the electric fielcl just outside the conductor is $\frac{\sigma}{\in_0}\hat{\text{n}}.$
  2. When a charged particle is moved from one point to the other on a closed loop, the work done by the electrostatic field is zero.
  3. Hence, the tangential component of electrostatic field Is continuous from one side of a charged surface to the other.

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