Question

How do you determine direction of induced current?

Answer 1

Hint:When the magnetic field present in a particular coil changes, the magnetic field linked with it also changes and hence current is induced into it. The induced current in the coil could be in any direction. To know which direction we will use a law called LENZ’S LAW and then apply MAXWELL’s right hand rule.

Complete step-by-step solution:
As mentioned in the hint above we are going to use Lenz's law to determine the direction of induced current. Let us $1^{st}$ know what this rule states.
Lenz’s Law: it states that the polarity of induced EMF is such that it always tends to produce a current which opposes the change in magnetic flux that produces it.
This can mathematically expressed as:
\[E = - N\dfrac{{\delta {\phi _B}}}{{\delta t}}\]
Here the negative sign implies that it opposes the initial magnetic field.
Let us consider an example to understand lenz’s law:
Consider a coil and a magnet, if the magnet is moving towards the coil the magnetic field changes due to which magnetic flux changes and current is induced. We to 1st check if the magnetic field lines are increasing or decreasing.
We also know that for a magnet, magnetic field lines move out from the north pole and towards the south pole. If the magnetic field increases the direction of induced current will be opposite, and if the magnetic field decreases the induced magnetic field will be in the same direction to replace the original field. Look at the image to get a better understanding.

As the north pole is facing the coil ,magnetic flux is also in the same direction and hence by Lenz's law the induced current should oppose it , hence $i_1$ and $i_2$ are in opposite directions to the magnet’s north pole.
Now, align your thumb in the direction of the magnetic field (in the figure given by I and i1), and curl your fingers to get the direction of induced current. By doing the same thing in the above figure we see that in the front part of the coil induced current direction is upwards and behind the coil it is downwards.

Note:Induced current lasts only till the magnetic flux in the coil keeps changing. The induced EMF is larger if \[{\phi _B}\]changes rapidly. We can also use Fleming’s right hand thumb rule to determine the direction of induced EMF.