Question

Work done in moving a charge along the axis of circle having charge q

Answer 1

Think about the field lines from the charge at the centre of the circle.
You should know equipotential lines cross field lines at 90 degrees. Equipotentials are the equivalent of contour lines for a hill. If you follow a contour, you do not do any work going up or down the hill because you are staying at the same height.
You can also cheat a bit with this question. There are no numbers in the question so you know the answer cant be 7 joules or something like that because it would surely depend on the size of the charge/ the diameter of the circle etc. There must be some fundamental reason why there is an answer.
The first 2 paragraphs should give you sufficient pointers as to how to proceed.

Answer 2

heya dear!!!!

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work done moving along axis circle is zero.

because the angles between the components are normal hence it is zero work done here.


cos90=o

>>>>
$hapy \:$


w=f cos 90°