A square loop of side  cm carries a current  A. Calculate magnetic induction  (in T) at point , lying on the axis of loop and at a distance  cm from the centre loop

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Axis of the loop means a line passing through centre of loop and normal to its plane. Since distance of the point  is  from centre of loop and side of square loop is a as shown in figure (a)

Therefore, perpendicular distance of  from each side of the loop is,

Now, consider only one side  of the loop as shown in figure (b)

Magnitude of magnetic induction at , due to current in this side , is

Now, consider magnetic inductions, produced by currents in two opposite sides  and  as shown in figure

Components of these magnetic inductions, parallel to plane of loop neutralize each other. Hence, resultant of these two magnetic induction is  (along the axis)

Similarly, resultant of magnetic inductions produced by currents in remaining two opposite sides  and  will also be equal to  (along the axis in same direction). Hence, resultant magnetic induction