Predict the direction of induced current in the situations described by the following Figs. 6.18(a) to (f ).
(a)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
In the given circuit the South Pole is moving towards the right end of the coil, hence the polarity of induced emf will produce a current such that a south pole is induced on the right end of the coil.
Accordingly, the direction of induced emf should be qrpq.
(b)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
In the given circuit the South pole is moving towards the right end of the coil A, hence the polarity of induced emf will produce a current such that a south pole is induced on the right end of the coil A.
Accordingly, the direction of induced emf in coil A should be prq.
In coil B , the north pole is moving away from the left end. Hence the polarity of induced emf should be such that it will produce a current such that a south pole is induced on the left end of coil B.
Accordingly, the direction of induced emf in coil A should be yzx..
c)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
In the given circuit the when the tapping key is just closed the current starts to flow in coil A in clockwise direction, hence the direction of magnetic flux lines are towards left to right in coil B.
To oppose this an emf will be induced in coil B that will produce a current such that it produces a flux going from right to left.
Accordingly, the direction of induced emf in coil B should be yzx.
d)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
In coil A when the rheostat setting is changed as shown, the resistance increases and hence the current flowing through it decreases and also its magnetic flux decreases. Hence according to Lenz’s law an emf will be induced in coil B that produces a current to increase the flux through coil A.
Accordingly, the direction of induced emf in coil B should be yzx.
e)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
In coil A when the tapping key is just released, the current and hence the flux suddenly become zero Hence according to Lenz’s law an emf will be induced in coil B that produces a current to increase the flux through coil A.
Accordingly, the direction of induced emf in coil B should be xry.
f)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
As the current in the conductor decreases, so will the flux in the coil. However, all the field lines lie in the plane of the coil, hence no emf is induced in it.
(a)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
In the given circuit the South Pole is moving towards the right end of the coil, hence the polarity of induced emf will produce a current such that a south pole is induced on the right end of the coil.
Accordingly, the direction of induced emf should be qrpq.
(b)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
In the given circuit the South pole is moving towards the right end of the coil A, hence the polarity of induced emf will produce a current such that a south pole is induced on the right end of the coil A.
Accordingly, the direction of induced emf in coil A should be prq.
In coil B , the north pole is moving away from the left end. Hence the polarity of induced emf should be such that it will produce a current such that a south pole is induced on the left end of coil B.
Accordingly, the direction of induced emf in coil A should be yzx..
c)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
In the given circuit the when the tapping key is just closed the current starts to flow in coil A in clockwise direction, hence the direction of magnetic flux lines are towards left to right in coil B.
To oppose this an emf will be induced in coil B that will produce a current such that it produces a flux going from right to left.
Accordingly, the direction of induced emf in coil B should be yzx.
d)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
In coil A when the rheostat setting is changed as shown, the resistance increases and hence the current flowing through it decreases and also its magnetic flux decreases. Hence according to Lenz’s law an emf will be induced in coil B that produces a current to increase the flux through coil A.
Accordingly, the direction of induced emf in coil B should be yzx.
e)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
In coil A when the tapping key is just released, the current and hence the flux suddenly become zero Hence according to Lenz’s law an emf will be induced in coil B that produces a current to increase the flux through coil A.
Accordingly, the direction of induced emf in coil B should be xry.
f)
Consider the diagram below.
According to Lenz’s law the polarity of induced emf is such that the current produced due to it opposes the change in magnetic flux that produced it in the first place.
As the current in the conductor decreases, so will the flux in the coil. However, all the field lines lie in the plane of the coil, hence no emf is induced in it.
