now lets study the magnetic force on a close
loop in uniform magnetic field. here you can
see this is a uniform magnetic field of induction
b vector. in which a close loop a-b-c-d carrying
a current i is placed. and this placed in
such a way that, its length l is perpendicular
to magnetic induction and, breadth b is parallel
to the direction of magnetic induction. here
in this situation if we calculate the force
on different segments of. this loop. here
we can see force. on. section a-b we just
see a-b section the current is flowing, parallel
to magnetic induction so here we can say the
force on it is zero. and if we calculate the
force on section b-c. here you can see in
this section b-c magnetic induction is toward
right and current is in, downward direction.
if i use my righthand palm rule. here we can
see i am pointing fingers in the direction
of magnetic induction and thumb. in downward
direction so my. palm face will pointing in
outward direction, so we can write its magnetic
force is b-i-l. in. outward direction. and
now we can see, force on wires segment c-d
will again be zero because. the wire section
is parallel to magnetic induction. so i l
cross b will be zero. and if we calculate
the magnetic force on wire section d-a. here
you can see magnetic induction is toward right
and current is in upward so if i use my righthand
palm rule. fingers pointing toward magnetic
induction thumb along the direction of current.
and my palm face is pointing in inward direction.
so it’ll be the same force b-i-l in. inward
direction. so here we can see the net force,
on loop. the total magnetic force. on loop
here is equal to zero. so we can write whenever
a close current carrying loop is placed in
a magnetic field uniform magnetic field. net
force acting on the close loop will always
be equal to zero. and this inference you can
also deduce directly from the previous section.
where we have studied, the total magnetic
force on a random shaped wire. if there is
a random shaped wire it experiences the magnetic
force b-i-l where l is the. straight line
length between the 2 edges of the wire this
we have studied that, in a magnetic induction.
b vector if we place a random shaped wire.
carrying a current i then it’ll experience
a force which is equivalent to the force which
will act if a straight wire is placed between
the ends ay and b. if it is l force experienced
by this wire will be. magnetic force will
be b, i l. as current is flowing from ay to
b the. magnetic force will be acting on it
in this direction. now if ay and b are joined
and the wire is made as a close loop here
l become zero and we can directly write. always
the force will be zero, if l is zero or the
wire is taking the shape of close loop. so
you can always keep, this note in your mind
that. total magnetic force. on a current carrying.
close loop. in uniform magnetic field. is
always. equal to zero. but here we can see
one more thing, in this situation as the wire
b-c is experiencing a force in outward direction.
and the wire, d-a is experiencing a force
in inward direction which we have written
here. as a force magnitude is same total force
is zero but here we can see that, the line
of forces are not, in same line, so these
2 forces will produce a couple end the coil
will experience a torque, so we can write
the total magnetic force on a current carrying
close loop in uniform magnetic field is always
equal to zero but. it may experience. a torque.
by magnetic force. i have written it may experience
because it is not necessary but always the
line of action of 2 forces are different.
if in some situation the line of action of
the 2 opposite forces are same then torque
may also be equal to zero. about magnetic
torque will discuss in the next section, in
detail.
