Q. At what distance along the central axis of a uniformly charged plastic disc of radius R is the magnitude of the electric field equal to one-half the magnitude of the field at the centre of the surface of the disc?

 6303  226 Electric Charges and Fields Report Error

Solution:

At a point on the axis of uniformly charged disc at a distance x above the centre of the disc, the magnitude of the electric fieid is
E =
but
Then,
or
Squaring both sides and multiplying by to obtain

Thus,
x =