Faraday's law and Lenz's law of electromagnetic induction
Faraday's laws of electromagnetic induction are fundamental principles in electrical engineering that describe the relationship between an electric circuit and a magnetic field. These laws are the bedrock for the operation of most modern electrical devices, including induction motors, generators, and transformers.
What is Faraday's First Law of Electromagnetic Induction?
Faraday's first law states that whenever a conductor is placed in a varying magnetic field, an electromotive force (EMF) is induced across the conductor. If the conductor forms a closed circuit, an induced current flows through it. The magnetic field can be varied in several ways:
- Moving the magnet relative to the conductor
- Moving the coil within the magnetic field
- Rotating the coil relative to the magnetic field direction
Faraday's Second Law of Electromagnetic Induction
Faraday's second law of electromagnetic induction quantifies the relationship. It states that the magnitude of the induced EMF is directly proportional to the rate of change of magnetic flux linkages with the coil. Magnetic flux linkage is defined as the product of the number of turns in the coil and the magnetic flux passing through each turn.
Key Formula: E = -N (dΦ/dt)
Where:
- E = Induced EMF (volts)
- N = Number of turns in the coil
- dΦ/dt = Rate of change of magnetic flux
Faraday's Law Formula Derivation
When a conductor moves in a magnetic field:
Initial flux linkage with the coil = NΦ₁ (Wb)
Final flux linkage with the coil = NΦ₂ (Wb)
Change in flux linkage = N(Φ₁ - Φ₂)
Let Φ₁ - Φ₂ = ΔΦ
Therefore, change in flux linkage = NΔΦ
Rate of change of flux linkage = NΔΦ/Δt
Taking the derivative: E = N(dΦ/dt)
According to Faraday's law, the rate of change of flux linkages equals the induced EMF.
What is Mutual Induction?
Mutual induction occurs when alternating current flowing in one coil produces an alternating magnetic field, and that magnetic field induces EMF in nearby magnetically linked coils. This phenomenon is fundamental to transformer operation.
Applications of Mutual Induction:
- Power transformers
- Induction motors
- Wireless charging systems
- Radio frequency transformers
Lenz's Law: Direction of Induced EMF
Lenz's law of electromagnetic induction determines the direction of induced EMF. It states that when EMF is induced according to Faraday's law, the polarity of the induced EMF opposes the cause of its production.
Complete Faraday's Law with Lenz's Law:
E = -N(dΦ/dt)
The negative sign indicates that the induced EMF opposes the change in magnetic flux, following the principle of energy conservation.
Applications of Faraday's Laws
Faraday's laws of electromagnetic induction are applied in numerous electrical devices:
Electric Generators: Convert mechanical energy to electrical energy using rotating coils in magnetic fields.
Electric Motors: Use electromagnetic induction to convert electrical energy into mechanical motion.
Transformers: Step up or step down AC voltage levels using mutual induction principles.
Inductors: Store energy in magnetic fields and oppose changes in current flow.
Frequently Asked Questions
What is the difference between Faraday's first and second law?
Faraday's first law explains when EMF is induced (varying magnetic field), while the second law quantifies the magnitude of induced EMF (rate of flux change).
Why is there a negative sign in Faraday's law formula?
The negative sign represents Lenz's law, indicating that induced EMF opposes the change causing it, ensuring energy conservation.
What are the units of EMF in Faraday's law?
EMF is measured in volts (V), magnetic flux in webers (Wb), and time in seconds (s).
[Also Read: Fleming's Left hand and Right hand Rule]