let us discuss the direction of induced current
in a coil due to electro magnetic induction.
here we can see, this is a situation in which
there’s a circular coil on which, an inward
magnetic induction is applied. and here we
can see if the magnetic induction increases
with time, obviously the flux linked with
he coil is changing due to which, an induced
e m f is produced in it which will, cause
a current to flow in the coil. here we can
see it carries a current or a current is induced
in anti clock wise direction. this is because
as magnetic field is increasing in inward
direction, the current caused by the electro
magnetic induction will flow in such a way,
so as to oppose the causes of induction. here,
as the current is flowing in anti clock wise
manner, it’ll start producing an outward
magnetic induction which will oppose the downward
increment of magnetic induction. the same
phenomena we can see here in a practical situation,
here we can see a circular coil connected
with a galvanometer. and a bar magnet with
its north pole facing toward the coil is brought
close to the coil. and here we can see the
magnetic field of north pole, will be passing
through the coil from right to left. and as
the magnet comes close to the coil, the flux
toward left through the coil is increasing,
so it induces an anti clock wise current in
the coil due to which its own magnetic induction,
is developed towards right direction which
will oppose the leftward increment of magnetic
induction, due to motion of magnet. or we
can say, as the magnet is brought close here
we can see the situation again, as the magnet
is brought close, the coil induces a current
in such a way that, the facing end of the
coil in front of the magnet, also behaves
like a north pole and it’ll have a tendency
to repel the magnet. as the 2 similar poles,
repel away from each other. so we can see
the motion of magnet, which is causing the
flux change in the coil, is being opposed
by the induced current direction. similarly
we can see a situation, this is similar to
the situation we’ve already discussed. here
the magnetic induction is in inward direction
and a circular coil is placed. but here we
can see the magnetic induction gradually decreases
with time. if it starts decreasing with time
we can see, a clock wise current starts flowing
in the coil because, the clock wise current
produces an inward magnetic induction which
will have a tendency to oppose the dic rement
in magnetic induction. and similar situation
is here we can see, if there’s a coil and
close to the coil, there’s another coil
placed. and in the 1st coil a battery is connected,
and if we close down the switch, here we can
see, there exist a clock wise current in the
1st coil, which produces a magnetic induction
from right to left, because of which automatically
a current is induced in the 2nd coil, but
after sometime when the current becomes constant,
the current in 2nd coil drops to zero because
no change in magnetic induction is their.
and initially there was a change because the
flux was increasing from zero to a specific
value. now we can see what happens when the
switch is open. if we open the switch, the
current drops to zero and magnetic induction
of the 1st coil decreases. now we can see
in the 2nd coil current induces in the same
direction as that of the 1st coil because,
as the magnetic induction from right to left
is decreasing, it is developing a magnetic
induction in same direction so as to oppose
the dic rement. it is quite an important phenomenon
again we can see as the current drops to zero,
the current finally in 2nd coil also becomes
zero because now there’s no change. so electro
magnetic induction phenomenon, causes an e
m f to be induced or a current to be induced,
only in the duration when the magnetic flux
is changing, when the magnetic flux becomes
constant, there exist no induced e m f or
no induced current in the circuit.
let us discuss some more experiments to demonstrate
electro magnetic induction and the direction
of induced current understanding by using
lenz law. here we can see this is an electrical
circuit, in which a wire ay b is connected
with a battery and a rheostat along with a
switch. and on the other side of the wire
ay b there’s a circular coil placed in the
same plane of the wire. now when the switch
is closed we can see in the loop of wire ay
b a clock wise current flows, and as soon
as current flows, current in wire ay b establishes
a magnetic induction, in the outward direction,
in the region of this loop. and here we can
see as soon as in outward direction magnetic
induction increases due to the current in
circuit, a clock wise current is induced in
the circular loop because, if an outward direction
magnetic induction increases, here we can
see, the current induced in the loop will
be in such a way, so as to decrease this increase
in magnetic flux or magnetic induction, that’s
why it is in clock wise direction because,
current in coil itself produces a downward
or inward magnetic induction. and in this
situation here we can see, if the resistance
of rheostat is decreased, we can see initially,
when the current is established, no magnetic
flux change is there in the loop so no e m
f or current is there in coil. but when the
resistance of rheostat is decreased, here
we can see the current in wire ay b increases,
and again the outward magnetic induction through
the loop due to wire ay b increases, and again
it causes a current in clock wise direction.
and here, if we decrease the resistance, we
can see the current is in clock wise manner,
because of increase in magnetic field. now
if we start increasing this resistance see
what happens, the current in the loop of wire
ay b starts decreasing, and the magnetic field
also start decreasing. due to which, an anti
clock wise current is induced in the loop,
in the coil because, it produces its magnetic
induction in outward direction which will
be opposing the dic rement in this outward
magnetic induction due to decrease in current,
by increasing the resistance. so this experiment
itself is a very good demonstration to understand,
the direction of induced current by lenz law
and its verification also.
