Question

Direction of induced EMF can be found from
(A). Lenz law
(B). Laplace law
(C). Fleming law
(D). None of the above

Answer 1

Hint: EMF (ElectroMotive Force) of a cell is defined as the absolute potential difference between the terminals of the battery in the open circuit that is the energy supplied by the battery to drive the unit charge around the circuit.
But here we have Induced EMF which is defined as the generation of potential difference in the coil whenever there is change in magnetic flux linked with the coil.
So, when the coil itself produces EMF without using any battery it is called an induced EMF and it lasts as long as there is change in magnetic flux linked with it.
The direction of induced EMF is given by the law which is based on the conservation of energy.

Complete step by step answer:
Change in electric field produces a magnetic field like that whenever magnetic flux changes it produces emf in the closed conducting loop.
The magnitude of induced emf is given by Faraday’s law and direction of induced emf is Lenz’s law.
Thus, the correct option is A.
Lenz’s law states that, “the direction of induced current is such that it opposes the change that induced it”. This is nothing but a consequence of the law of conservation energy.
Formula is given by:
$\varepsilon =-N\dfrac{d\Phi }{dt}$
Where, N - No. of turns of the coil
$\Phi$ - magnetic flux linked with each turn of the coil.
Here -ve sign gives the direction of induced emf, it indicates that emf is in such a direction that it opposes the cause that produces it.
To understand it more clearly, consider an example
Consider a bar magnet whose north-pole is pushed towards the closed coil. As the North-pole of the bar magnet moves towards the coil, the magnetic flux through the coil increases. Hence current is induced in the coil in such a direction that it opposes the increase in flux. This is possible only if the current in the coil is in a counter clockwise direction then its north pole faces the north pole which would result in repulsive force which opposes the motion.

Note: Option B is incorrect as Laplace law is related to pressure and not to induced emf.
In case of option C, there are two Fleming rules, they are: - Fleming’s left-hand rule and right-hand rule.
Fleming's Left-Hand Rule is used to find the direction of force/motion of the conductor in an electric motor when the magnetic field direction and the current direction are known. Fleming's right-hand rule (for generators) shows the direction of induced current when a conductor attached to a circuit moves in a magnetic field. It can be used to determine the direction of current in a generator's windings, which is they asked in question
Now here we get confused, but as they did not mention Fleming's right hand rule, so option A is the more accurate one.