Induction Motor: Electromagnets and Electromagnetic Induction

Introduction 

Magnetic or electromagnetic induction is the process of production of electromotive forces like voltage across an electric conductor in a magnetic field that is constantly changing. Michael Faraday in 1831 discovered induction and J. Maxwell gave it a mathematical description as the Faraday’s law of induction (Kim et al., 2014). The Faraday law was later named the Maxwell-Faraday equation, one of the four equations by Maxwell in the electromagnetism theory.

Electric Field Vs. Magnetic Field

A magnetic field can be defined as an exerted region surrounding the magnetic force. A magnetic field is obtained by moving around the electric charges. Lines are normally used to show the magnetic field direction. The electric fields are created in the particles' surroundings and it becomes electrically charged. During the charging process, the positive charges get drawn or attracted, while the negative ones get repelled.

Figure: Electric vs magnetic fields 

An object featuring a moving charge features typically both electric and magnetic fields. These fields have both similarities and differences. The two fields are interrelated and are referred to as electromagnetic fields, they, however, they are not dependent on each other: 

Table 1: Electric vs Magnetic Fields 

Application: Induction Motor

The electric motor device is used for altering the electrical energy into a mechanical one. On the other hand, the electric generator does the opposite of the electric motor, and it applies mechanical energy to create electricity. At the center of the two applications, a generator and a motor is a wire coil that hangs in a magnetic field. This one coil can be adopted for a generator or motor.

Figure: Single Phase Induction Motor

When the device is applied as a motor, a current is passed through the coil. The magnetic field interaction with this current causes the coil to move in a spinning motion. The device is used as a generator by spinning the coil through current induction.

An AC generator adopts the Faraday induction law, repeatedly spinning some coil in a magnetic field to generate oscillating emf ( Hagisawa & Ikeda, 1989) . The areas around the coil together with the magnetic field remains constant and as such the Faraday law is calculated as follows:

The emf expression can be simplified further to:

Faraday's law practical cases

Faraday law states that the induced voltage in circuitry is directly proportional to the level of change with the magnetic flux time via the circuit. A transformer is a perfect example of faradays law application.

The transformer uses Faraday’s law of induction. Transformers were an invention of Nikola Tesla. In a transformer, there are alternating currents that change directions several times every second. These charges are passed over a coil that is wrapped around some magnetic center/core. This generates an altering magnetic field at the center/core, which as a result induces a current in the second core. The traffic light is another application of Faraday’s law. The traffic lights use a wire loop to identify the effect of the induced magnetic field. When on the road, loops of wire with alternating current create a changing magnetic field. When the car drives nearby, the current generates an opposing magnetic field, which affects the current in the initial wire loop. The original wire loop shows the presence of a car, which triggers a change in light to dim.

In conclusion, Faraday’s law and induction are instrumental in daily human operations. With the advancement in technology, there are more and more applications for this law.

References 

Hagisawa, N., & Ikeda, H. (1989).  U.S. Patent No. 4,795,872 . Washington, DC: U.S. Patent 

and Trademark Office. 

Kim, D. K., Yoon, H., Kang, W. Y., Kim, Y. B., & Choi, H. T. (2014). Development of a 

spherical reaction wheel actuator using electromagnetic induction.  Aerospace science and technology ,  39 , 86-94.