Question

Draw the pattern of magnetic field lines produced around a current carrying straight conductor passing perpendicularly through a horizontal cardboard. State and apply right hand thumb rule to mark the direction of the field lines. How will the strength of the magnetic field change when the point where magnetic field is to be determined is moved away from the straight conductor? Give reasons to justify answer.

Answer 1

see attached figure, it gives us the patterns of magnetic field lines produced around a current carrying straight conductor passing perpendicularly through horizontal cardboard.

$\text{\underline{Right hand thumb rule}}$ : if the current carrying conductor is held in the right hand in such a way that thumb point in the direction of current, then direction of the curl of the fingers will give the direction of the magnetic field. it is understood by shown below figure.

we know, strength of magnetic field is inversely proportional to separation between two consecutive magnetic lines of forces.

we also know, density of magnetic lines of forces decreases when we move away from the straight conductor. it means, separation between two magnetic lines of forces increases when we move away from the straight conductor.

so, magnetic strength decreases when we move away from the straight conductor.

Answer 2

Answer:

Right hand thumb rule : If we hold the current carrying conductor in the right hand such that the thumb points in the direction of current, then the fingers encircle the wire in the direction of magnetic lines of force. The strength of the magnetic field will reduce when the point where magnetic field is to be determined is moved away from the straight conductor as B ∝ r.