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EM Induction

Super Fast Trains Superfast trains that levitate from the rail track This is the fastest developing age of Science and Technology. The latest technological development aims at the fastest mode of transport using superconductors that possess zero resistance at very low temperatures. Superconducting material helps to lift the object from its surface. This is known as Meissner Effect. The present day search for the room temperature super conductors is still in progress. One may ask, what is the reason for levitation? what are magnetic levitation trains? Let's dwell more as we move in to this topic.

Learning objectives

After completing the topic, the student will be able to:

  • Discover and explore how a varying magnetic field produces a change in emf based on the Faraday's experiments of electromagnetic induction.
  • Determine the magnetic flux through any surface and explore the laws of EM induction using the concept of magnetic flux.
  • Explore the reason for the effect (induced current) to oppose the cause (changing magnetic field) and expand its applications.
  • Investigate the concept of eddy currents and its applications in everyday science.
  • Discuss the types of inductions and probe their applications in transformers, and other electrical devices.
  • Investigate and explore about the inductors and its applications in various LR circuits.
  • Develop an LC circuit and demonstrate its applications in various electrical devices.
Dynamo Dynamo It is a simple generator or machine that transforms mechanical energy into electrical energy. A dynamo in basic form consists of a powerful field magnet where its poles lie in between a suitable conductor, usually in the form of a coil (armature). When there is a change in magnetic field produced due to its movement (to and fro direction or through rotation), an induced current flows through the wire. Thus the mechanical energy of rotation converts into an electric current in the coil which can be used for glowing a filament of the bulb.
Faraday's discovery

Up to this point we have seen the interplay between moving charge (electric current) and magnetic field. What would happen on a charge if the magnetic field were to move around?

Michael Faraday, through many experiments, established that though a steady magnetic field cannot produce electricity, a varying magnetic field does. The currents produced in his experiments were small and lasting for a short duration. When he demonstrated his discovery before a gathering, a lady is said to have asked him what use that could be. At that period of time very few applications of electricity were known.

Faraday replied that his discovery was like a new born baby; one cannot know what the baby will achieve after growing up. Faraday's baby has proved to be extraordinarily successful as an adult. It would not be an exaggeration to say that Faraday's discovery was one of the most important discoveries of the 19th century from the point of practical applications of electricity as well as understanding of electromagnetic field. Electrical engineering and electronics have shown the immense potentialities for applications of Faraday's discovery.

Faraday and Henry separately established that electric current can be produced in a wire simply by moving a magnet in or out of a coiled part of the wire. The motion of a magnet in a wire loop itself induces voltage in the loop. No external voltage source or battery is needed. Voltage is caused, or induced by the relative motion between a wire and a magnetic field. Voltage is induced whether the magnetic field of a magnet moves near a stationary conductor or the conductor moves in a stationary magnetic field. In both the cases the voltage induced is the same for the same relative motion.

Voltage Voltage Voltage is induced in the wire loop either when the magnetic field moves past the wire or the wire moves through the magnetic field.
Electromagnetic induction

The greater the number of loops of wire that moves in a magnetic field, the greater is the induced voltage. Pushing a magnet into thrice as many loops will induce thrice as much voltage; pushing into hundred times as many loops will induce hundred times as much voltage; and so on.

If the coil is connected to a resistor or other energy–dissipating device, it can be found that it is more difficult to push the magnet into a coil made up of more loops. This is because the induced voltage makes a current, which makes an electromagnet, which repels the magnet in our hand. More loops mean more voltage which means we do more work to induce it.

The amount of voltage induced depends on how fast the magnetic field lines are entering or leaving the coil. Very slow motion produces hardly any voltage at all. Quick motion induces a greater voltage. This phenomenon of inducing voltage by changing the magnetic field in a coil of wire is called electromagnetic induction.

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