Question

A long cylindrical shell carries positive surface charge ${}^{\prime }{\sigma }^{\prime }$ in the upper half and negative surface charge ${}^{\prime }-{\sigma }^{\prime }$ in the lower half. The electric field lines around the cylinder will look like figure given in:
(figures are schematic and not drawn to scale)
A.

B.

C.

D.

Answer 1

Hint: Electric field lines can be defined as the imaginary lines propagating through space. No charge is enclosed in a long cylindrical shell. We know, if there are no charges enclosed then no electric field lines will be generated. Also, the electric field lines always start at a positive charge and end at a negative charge. This basic information can be used to answer the given question.

Complete answer:
There is no charge enclosed inside a cylindrical shell. Hence, the electric field inside a shell will be zero. Thus, there will be no electric field lines inside. It is given that the shell carries positive surface charge ${}^{\prime }{\sigma }^{\prime }$ in the upper half and negative surface charge ${}^{\prime }-{\sigma }^{\prime }$ in the lower half. We know the direction of the electric field is always directed away from the positive charge and towards the negative charge. So, the electric field lines will originate from positive charges radially to the surface and terminate at the negative charges radially inwards to the surface.

Thus, the correct answer is option A.

Note:
To solve these types of questions, students must have clear knowledge about electrostatics. Students should know about the properties of electric field lines. The electric field lines are always perpendicular to the surface charge. The number of field lines is directly proportional to the magnitude of charge. If there is a single positive charge then the electric field lines end at infinity and if there is a single negative charge then the electric field lines start at infinity.