To put it in a nutshell, if one did not study the chapter magnetic effects of current, then one would not have an appreciation for electricity, working of transformers, motors, generators etc. Simply put, you would be one of the many people who only know how to use electricity and electrical appliances without understanding the working principle behind it. read more : marketingproof
When an electric current flow through a conductor, it creates a magnetic field around it. The direction of the magnetic field is dependent on the direction of flow of current by placing the thumb of the right hand, along the direction of flow of current. The direction in which the rest of the fingers curl around the conductor, denotes the magnetic field direction to be wither clockwise or anti clockwise. This is called as the Right-Hand Thumb Rule. On paper, it is visualized by imagining an arrow. If the current is going away from the observer, then one can imagine an arrow moving away. When noticed from this position, the observer can only see the tail of the arrow like a cross. So, to represent the direction of current moving from the observer, a cross X is written on paper and circular lines of magnetic field are drawn around it. The direction of the magnetic field will be clockwise. When the current is moving towards the observer, then an arrow is imagined to be moving towards him and it is represented by a dot with concentric circles around it. The direction of the magnetic field is then anti clockwise in nature. Like electric field, magnetic field is also a vector quantity. It has both direction and magnitude. Magnetic field strength is measured in units of Tesla and is represented by the letter B.
The interaction of electricity, magnetic effect of current and magnetism can be understood by the Faradays Laws of electromagnetism. Faradays Laws can be explained in the following points, that explains the concept of generation of electromotive force (EMF) as experiencing a force. Both the above effects, are utilized in modern science through the application in generators and motors.
- When a conductor is placed in a varying magnetic field, then an electromotive force is developed across the ends of the conductor.
- The magnitude of induced EMF is directly proportional the rate of flux linkage.
- A current carrying conductor when placed in a magnetic field, experiences force on it.
The first law can be understood simply by understanding that for EMF to be induced in any conductor, there must be a relative change in the number of magnetic lines of flux being cut. That means, that there should be a varying flux linkage between the conductor and the magnetic field. This can be accomplished through either changing the strength of the magnetic field continuously (like a sinusoid), or by keeping the magnetic field strength constant and moving the conductor in the magnetic field. In case the conductor circuit is a closed path, then there will be an induction of current in the circuit and this is called as induced current. This is fundamental behind the working of an electric generator.
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The next important point is that if a conductor that already has a current flowing in it, is placed in a magnetic field, then it will experience a force. This is because we must remember that the magnetic field is a vector quantity. When a current carrying conductor exists, then it creates a magnetic field around it. This magnetic field interacts with the second magnetic field, and it leads to a resultant magnetic field out of it. This is the fundamental behind the working of a motor. In order to explain this, let us study the working of a 3-phase induction motor.
Do you know the answer of the below question?
- Two parallel wires carrying current in the same direction attract each other while two beams of electrons travelling in the same direction repel each other. Why?
3-phase induction motor
There are three important components of an induction motor, namely, stator, uniform air gap and rotor. When a three phase electric supply is connected to the three phases of the stator winding, then it leads to the currents flowing in each individual stator winding. This is now a current carrying conductor. Each of these conductors creates its own magnetic field, and the three magnetic fields interact with each other to create a resultant magnetic field which is rotating in nature. Thus, now we have a varying magnetic field in the uniform airgap of the induction motor. This field now interacts with the rotor conductors and based on faradays first law, it leads to the induction of EMF across the ends of the rotor conductor. However, this rotor circuit is a closed path and therefore, the emf creates an induced current in the conductor. As we all know, a current carrying conductor creates a magnetic field, thus the rotor current also creates a magnetic field. Now because it is a current carrying conductor placed in a rotating magnetic field, therefore, the rotor conductor experiences a mechanical force on it, leading to the rotation of the rotor, and hence the shaft which gives mechanical output. The direction of rotation is based on Lenz’s law.
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