0A Brief Introduction
Electromagnetic Induction is the basic principle of operation of Electrical Machines such as transformers, motors and generators. Therefore its a critical topic in Physics. As a process, Electromagnetic Induction is the process of using magnetic fields to produce voltage, and in a closed circuit, a current.
Angle Between Area of the Loop and Magnetic Field
Understand that there is an Orientation between B and Area Loop, which matters. This helps ensure that the Magnetic Flux is calculated correctly. The B A Cos(Theta) is the dot product of Magnetic Field (B) and the Area Loop vector shown perpendicular to the loop. It gives is magnetic Flux (Φ).
Generally, we would have a constant Magnetic Field (B) in the Numerical. i.e. it will not vary. But if you are given a Magnetic Field that changes (variable Magnetic Field), then you must apply Integration to get the flux. (JEE/NEET Students to note this)
Understand Faraday's's Law of Induction in-depth - Read the numerical carefully. Try to identify the reason why the flux through the loop is changing. This change in flux will result in EMF. Following possibilities could arise:-
1) Change in Angle between B and A ( Area vector). This changes flux, i.e. there is a flux rate.
2) Linear Motion of the Metallic Rod placed on a Rectangular Wire ( Area of loop changes). This also results in the rate of change of flux. ( Blv where v is the velocity of the conductor. Increase the speed, i.e. relative motion and get higher emf. Note that Relative Speed is covered in class XI. Reread it)
3) Rotation of the conductor that cuts the flux. This also is a change of flux and hence induced emf. You would see Angular velocity in such questions.
When you make more than 1 Turn on the coil, then each Turn experiences a change in magnetic flux. Thus more the Turns in the Coil higher is the Emf produced.
Use the Faraday law to calculate the magnitude of the emf. Practise at least 20 Question on Faraday's's law.
Most of the time the rate at which flux changes with time would be constant so the emf will be constant but you can have a situation where the rate of change of flux d(ψ)/dt is variable. But there can be a situation where the rate of change of flux is not a constant number. It is a variable. (JEE/NEET Students to note)
Lenz's Law
Use Le's's law to find the direction of induced emf and induced current. This is very important. Most of the students dont understand the significance of the negative sign of d(phi)/dt. Don't Ignore L's's Law. Practise at least 10 Questions that help you know Le's's law. The emf induced in the coil is popularly called Back emf ( the direction of the induced emf is such that it will always opposes the change that is causing it)
When you are doing Le's's law numerical you will get directions of induced current as Clockwise, Anto Clockwise.
Example
Think of a Situation when a circular Ring is thrown in the magnetic field. When the flux through it is changing as it is entering or leaving the Magnetic Field EMF will get generated. But when it leaves the Magnetic Field completely or is yet to enter the Field, the EMF does not exist. This is obvious because we need a d(Φ)/d(t)
