Electromagnetic Induction for JEE/NEET
Electromagnetic induction is a fundamental phenomenon in physics that describes the production of an electromotive force (EMF) or voltage across an electrical conductor within a changing magnetic field. This concept, discovered by Michael Faraday in the 19th century, forms the basis for many essential technologies, including generators, transformers, and wireless charging.
Faraday’s Law of Induction
Faraday’s law quantifies the relationship between a changing magnetic field and the induced EMF. It states that the magnitude of the induced EMF is proportional to the rate of change of magnetic flux through a circuit.
Magnetic Flux (Φ): A measure of the total magnetic field lines passing through a given area. It’s calculated as the product of the magnetic field strength (B), the area (A) it passes through, and the cosine of the angle (θ) between the magnetic field and the normal to the area:
- Φ = BAcosθ
Induced EMF (ε): The EMF generated in a circuit due to the changing magnetic flux. Faraday’s law states:
- ε = – dΦ/dt (The negative sign indicates the direction of the induced EMF, as explained by Lenz’s law.)
Lenz’s Law
Lenz’s law explains the direction of the induced EMF and current. It states that the direction of the induced EMF is such that it opposes the change in magnetic flux that produced it. This opposition arises from the conservation of energy.
Methods of Inducing EMF
- Changing the magnetic field strength: Increasing or decreasing the strength of the magnetic field passing through a coil will induce an EMF.
- Changing the area of the loop: Expanding or contracting a loop of wire within a magnetic field changes the magnetic flux and induces an EMF.
- Changing the orientation of the loop: Rotating a loop of wire in a magnetic field changes the angle between the magnetic field and the loop’s area, inducing an EMF.
Applications of Electromagnetic Induction
Electromagnetic induction is the foundation for a wide range of technologies, including:
- Electrical Generators: Convert mechanical energy (e.g., from turbines) into electrical energy by rotating a coil in a magnetic field.
- Transformers: Change the voltage of alternating current (AC) power by utilizing electromagnetic induction between two coils wound around a common core. This enables efficient power transmission over long distances.
- Wireless Charging: Uses electromagnetic induction to transfer energy wirelessly between a charging pad and a compatible device.
- Induction Cooktops: Generate heat in cookware by inducing eddy currents in the base of the pan.
- Magnetic Brakes: Utilize eddy currents to create braking forces in vehicles and machinery.
Electromagnetic Induction for JEE/NEET- Eddy Currents
Eddy currents are circulating currents induced in conductors when exposed to changing magnetic fields. They can be useful for applications like braking and induction heating, but they can also cause energy loss in transformers and other devices.
Inductance
Inductance is the property of a circuit element that opposes changes in current. It arises from the magnetic field generated by the current itself. Self-inductance refers to the inductance of a single coil, while mutual inductance describes the inductance between two coils.