Magnetic ?eld is a vector quantity {vector B}, therefore, it has two components to represent it: Magnitude {B}, and
direction.

To ?nd the direction, Right Hand Thumb Rule is used, while for magnitude, a basic law of Biot-Savart Law is used.
Right Hand Thumb Rule [RHTR} states {in my words} that

- if you are given a current {I} carrying conductor, a magnetic ?eld {B} is produced around it.

- The magnetic ?eld lines are in concentric circles, in plane perpendicular to the direction of current.

-It you told your right hand four ?ngers, and keep your thumb straight. If the current is in the direction of thumb,
then magnetic ?eld (due to the current} lines will be along the direction of ?ngers.

NOTE: The direction of magnetic ?eld direction is represented by ?eld or force lines.

NOTE: denser the ?eld lines {i.e., large number of ?eld lines concentrated some where) == strong ?eld; and vice-
a-versa.

This concept is applicable in the case of solenoid, you have shown and have asked for. To explain you, I have
attached my camera pictures. May be the quality of the picture not so good, but please bear with me.
ln the attachments, I have started with RHTR:
Because,
Solenoid {picture you have shown in attachment): N number of loops, side-by-side == conductors in shape of
loop, parallel to one another.

Page 1

-First: Single conductor and ?eld around it [in a plane perpendicular to the direction of current)

-lf no. of conductors are placed sided-by-side, the ?eld lines will be combination of all of them [see Attachment ?"
combined ?eld lines are darkened)

Page 2

-Now take an example of rectangularrsquare loop, combined ?led of four sides - four conductors. Inside the loop,
?eld will be in the same direction {for each apply RHTR). Outside the loop, ?eld direction will be opposite to that of
inside ?eld. Outside, each side of the loop, ?eld will be dominated by a conductor closer to it. Though, inside, ?eld
is combined of all sides. Obviously, inside the ?eld will be stronger than outside.

-Now replace square loop with circular loop == Very large number of conductors side by side, with a small
deviation of angle with respecto one another. But concept of loop will be applied, except instead of 4 conductors,
very large number of conductors.

-Once single loop is done, now extend further: N number of loops side by side == N conductors side~by-side,
each in shape of a loop. Now you see the combined ?eld lines pro?le [see attachment}

Attachment:- follow up solenoid.docx