$A$ straight conductor passes vertically through a cardboard sprinkled with iron filings. Show the setting of iron filings when a weak current is passed in the downward direction and then the cardboard is gently tapped. Draw arrows to represent the direction of magnetic field lines.
What changes occur if,
$(i)$ the strength of current is increased?
$(ii)$ the single conductor is replaced by several parallel conductors each carrying same current flowing in the same direction?

(N/A) The image shows the pattern in which iron filings will set themselves. The arrows show the direction of magnetic field lines,which is clockwise for a downward current.
$(i)$ The arrangement of iron filings remains unchanged,but they get arranged up to a larger distance from the conductor when the strength of current is increased. This is because on increasing the strength of current,the strength of the magnetic field increases and it becomes effective up to a larger distance from the conductor.
$(ii)$ This increases the total magnetic field strength,as such the iron filings get arranged up to a larger distance from the conductors.