Page 8 - Electrostatics 11 class

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brought near its end P as shown in figure(a). So that the opposite charge (-

ve) is induced at the nearer end P and the similar charge (+ve) is induced at
the remote end Q.
❖ The end Q of the body id earthed i.e.; it is connected with the earth with the

help of a conducting wire so that the free charges (-ve ) flows to the earth.
❖ The earthing wire is now disconnected keeping the body A still in its
position as shown in figure (c ).
❖ Finally, the body A is removed from its position so that the +ve charges

spread all over in the body B. In this way the body can be charged
positively.

Action of points:

The leakage of charge from sharp points is called action of point.

☻ The distribution of charge over the surface of a conductor is uniform
only when the surface is uniform shaped.
☻ The density of charge at any part of

conductor is inversely proportional to the
radius of curvature of the surface of that part.

i.e., (σ = ⟹ ∝ )

☻ It is greater on those parts of the surface

which have the greater curvature (least radius of curvature).
☻ Hence, density of charge at the pointed parts of a conductor is very large.
☻ E.g., The air particles and dust particles coming in contact gain charge

from the sharp points by conduction.
Uses of Action of points:
☻ The lightning conductor are made pointed upward in order to have a safe

discharge of the electricity generated in the atmosphere.
☻ The electric poles supporting the transmission lines at high voltage are
fitted with a sharp pointed conductor at the top. If there is any leakage of
charge from the line to the poles, it is discharged into the atmosphere

through the pointed ends.

☻ Sharp edges or points are strictly avoided in electrical machines.

8 Electrostatics