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When a DC current passes through a long straight conductor a magnetising force, H and a static Magnetic Field, B is developed around it If the wire is then wound into a coil, the magnetic field is greatly intensified producing a static magnetic field around itself forming the shape of a bar magnet giving a distinct North and South pole.
The magnetic flux developed around the coil being proportional to the amount of current flowing in the coils windings as shown. If additional layers of wire are wound upon the same coil with the same current flowing through them, the static magnetic field strength would be increased.
Therefore, the magnetic field strength of a coil is determined by the ampere turns of the coil. With more turns of wire within the coil, the greater the strength of the static magnetic field around it.
But what if we reversed this idea by disconnecting the electrical current from the coil and instead of a hollow core we placed a bar magnet inside the core of the coil of wire. By moving this bar magnet “in” and “out” of the coil a current would be induced into the coil by the physical movement of the magnetic flux inside it.
Likewise, if we kept the bar magnet stationary and moved the coil back and forth within the magnetic field an electric current would be induced in the coil. Then by either moving the wire or changing the magnetic field we can induce a voltage and current within the coil and this process is known as Electromagnetic Induction and is the basic principle of operation of transformers, motors and generators.
Electromagnetic Induction was first discovered way back in the 1830’s by Michael Faraday. Faraday noticed that when he moved a permanent magnet in and out of a coil or a single loop of wire it induced an ElectroMotive Force or emf, in other words a Voltage, and therefore a current was produced.
So what Michael Faraday discovered was a way of producing an electrical current in a circuit by using only the force of a magnetic field and not batteries. This then lead to a very important law linking electricity with Magnetism, Faraday’s Law of Electromagnetic Induction.
When the magnet shown below is moved “towards” the coil, the pointer or needle of the Galvanometer, which is basically a very sensitive centre zero’ed moving-coil ammeter, will deflect away from its centre position in one direction only. When the magnet stops moving and is held stationary with regards to the coil the needle of the galvanometer returns back to zero as there is no physical movement of the magnetic field.
Likewise, when the magnet is moved “away” from the coil in the other direction, the needle of the galvanometer deflects in the opposite direction with regards to the first indicating a change in polarity. Then by moving the magnet back and forth towards the coil the needle of the galvanometer will deflect left or right, positive or negative, relative to the directional motion of the magnet.
Electromagnetic Induction by a Moving Magnet
Likewise, if the magnet is now held stationary and ONLY the coil is moved towards or away from the magnet the needle of the galvanometer will also deflect in either direction. Then the action of moving a coil or loop of wire through a magnetic field induces a voltage in the coil with the magnitude of this induced voltage being proportional to the speed or velocity of the movement.
Then we can see that the faster the movement of the magnetic field the greater will be the induced emf or voltage in the coil, so for Faraday’s law to hold true there must be “relative motion” or movement between the coil and the magnetic field and either the magnetic field, the coil or both can move.
Faraday’s Law of Induction
From the above description we can say that a relationship exists between an electrical voltage and a changing magnetic field to which Michael Faraday’s famous law of electromagnetic induction states: “that a voltage is induced in a circuit whenever relative motion exists between a conductor and a magnetic field and that the magnitude of this voltage is proportional to the rate of change of the flux”.
Electric motor, any of a class of devices that convert electrical energy to mechanical energy, usually by employing electromagnetic phenomena. Most electric motors develop their mechanical torque by the interaction of Conductors carrying current in a direction at right angles to a magnetic field. The various types of electric motor differ in the ways in which the conductors and the field are arranged and also in the control that can be exercised over mechanical output torque, speed, and position.
Principle of operation
The basic principle on which motors operate is Ampere's law. This law states that a wire carrying an electric current produces a magnetic field around itself. Imagine that current is flowing through The presence of that current creates a magnetic field around the wire. Since the loop itself has become a magnet, one side of it will be attracted to the north (N) pole of the surrounding magnet and the other side will be attracted to the south (S) pole of the magnet. The loop will begin to rotate.
AC motors. What happens next depends on the kind of electric current used to run the motor, direct (DC) or alternating (AC) current. With AC current, the direction in which the current flows changes back and forth rapidly and at a regular rate.
In the United States, the rate of change is 60 times per second, or 60 hertz (the unit of frequency).
In an AC motor, then, the current flows first in one direction through the wire loop and then reverses itself about 1/60 second later. This change of direction means that the magnetic field produced around the loop also changes once every 1/60 second. At one instant, one part of the loop is attracted by the north pole of the magnet, and at the next instant, it is attracted by the south pole of the magnet.
But this shifting of the magnetic field is necessary to keep the motor operating. When the current is flowing in one direction, the right hand side of the coil might become the south pole of the loop magnet. It would be repelled by the south pole of the outside magnet and attracted by the north pole of the outside magnet. The wire loop would be twisted around until the right side of the loop had completed half a revolution and was next to the north pole of the outside magnet.
If nothing further happened, the loop would come to a stop, since two opposite magnetic poles—one from the outside magnet and one from the wire loop—would be adjacent to (located next to) each other. And unlike magnetic poles attract each other. But something further does happen. The current changes direction, and so does the magnetic field around the wire loop. The side of the loop that was previously attracted to the north pole is now attracted to the south pole, and vice versa. Therefore, the loop receives another "kick," twisting it around on its axis in response to the new forces of magnetic attraction and repulsion.
Thus, as long as the current continues to change direction, the wire loop is forced to spin around on its axis. This spinning motion can be used to operate any one of the electrical appliances mentioned above.
Capacitor
A capacitor is a device for storing electrical energy. Capacitors are used in a wide variety of applications today. Engineers use large banks of capacitors, for example, to test the performance of an electrical circuit when struck by a bolt of lighting. The energy released by these large capacitors is similar to the lightning bolt. On another scale, a camera flash works by storing energy in a capacitor and then releasing it to cause a quick bright flash of Light. On the smallest scale, capacitors are used in computer systems. A charged capacitor represents the number 1 and an uncharged capacitor a 0 in the binary Number System used by computers.
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Electromagnetic induction is the production of an electric current in a conductor due to a changing magnetic field. This phenomenon was first discovered by Michael Faraday in 1831, and it has since become one of the most important concepts in physics and engineering.
Faraday’s law of induction states that the magnitude of the induced electromotive force (EMF) is equal to the rate of change of the magnetic flux through the conductor. The direction of the induced EMF is given by Lenz’s law, which states that the induced current will flow in a direction such that it opposes the change that produced it.
Mutual inductance is the phenomenon in which an electric current in one coil of wire induces an EMF in a nearby coil of wire. The amount of mutual inductance between two coils depends on their geometry and the permeability of the medium between them.
Self-inductance is the property of an inductor to store energy in a magnetic field. The amount of self-inductance of an inductor is proportional to the square of the number of turns in the inductor and the permeability of the medium around it.
Inductance is a measure of the ability of a conductor to store energy in a magnetic field. The unit of inductance is the henry (H).
Eddy currents are electric currents that flow in closed loops within a conductor when a changing magnetic field is applied to the conductor. Eddy currents can cause significant heating of the conductor, and they can also cause noise and vibration.
A transformer is a device that uses electromagnetic induction to transfer electrical energy from one circuit to another. Transformers are used in a wide variety of applications, including power transmission, power distribution, and audio and video equipment.
Rotating machines are devices that convert mechanical energy into electrical energy or vice versa. Rotating machines include generators, motors, and alternators.
Induction heating is a process of heating materials by passing an alternating current through a coil of wire that is placed near the material. The alternating current creates a magnetic field, which induces an eddy current in the material. The eddy currents cause the material to heat up.
Electromagnetic compatibility (EMC) is the ability of electronic equipment to operate properly in the presence of electromagnetic interference (EMI). EMI can be caused by natural sources, such as lightning, or by man-made sources, such as power lines and radio transmitters.
Electromagnetic radiation is a form of energy that is transmitted through space or through a material medium in the form of waves. Electromagnetic radiation can be classified into two types: non-ionizing radiation and ionizing radiation. Non-ionizing radiation does not have enough energy to remove electrons from atoms or Molecules, while ionizing radiation does.
The electromagnetic field is a physical field that is produced by the movement of electric charges. The electromagnetic field is responsible for the electromagnetic force, which is one of the four fundamental forces of nature.
Maxwell’s equations are a set of four equations that describe the fundamental laws of electromagnetism. Maxwell’s equations were first published in 1864 by James Clerk Maxwell.
Electromagnetism is the study of the interaction between Electricity and Magnetism. Electromagnetism is one of the four fundamental forces of nature, and it is responsible for a wide variety of phenomena, including electricity, magnetism, light, and radio waves.
Electricity is the flow of electrons through a conductor. Electricity is used to power a wide variety of devices, including lights, motors, and computers.
Magnetism is the force that attracts or repels certain materials. Magnetism is used in a wide variety of devices, including compasses, motors, and generators.
1. What is the difference between a conductor and an insulator?
A conductor is a material that allows electricity to flow through it easily. An insulator is a material that does not allow electricity to flow through it easily.
2. What is the difference between direct current (DC) and alternating current (AC)?
Direct current (DC) is electricity that flows in one direction. Alternating current (AC) is electricity that flows in two directions, back and forth.
3. What is the difference between a battery and a capacitor?
A battery is a device that stores energy in the form of chemical reactions. A capacitor is a device that stores energy in the form of an electric field.
4. What is the difference between a resistor and a capacitor?
A resistor is a device that resists the flow of electricity. A capacitor is a device that stores energy in the form of an electric field.
5. What is the difference between a diode and a transistor?
A diode is a device that allows electricity to flow in one direction only. A transistor is a device that can be used to amplify or switch electrical signals.
6. What is the difference between a transformer and an inductor?
A transformer is a device that transfers electrical energy from one circuit to another. An inductor is a device that stores energy in the form of a magnetic field.
7. What is the difference between a motor and a Generator?
A motor is a device that converts electrical energy into mechanical energy. A generator is a device that converts mechanical energy into electrical energy.
8. What is the difference between a light bulb and a fluorescent lamp?
A light bulb is a device that produces light by heating a filament. A fluorescent lamp is a device that produces light by passing electricity through a gas.
9. What is the difference between a solar cell and a photovoltaic cell?
A solar cell is a device that converts sunlight into electrical energy. A photovoltaic cell is a device that converts light into electrical energy.
10. What is the difference between a battery and a fuel cell?
A battery is a device that stores energy in the form of chemical reactions. A fuel cell is a device that converts chemical energy into electrical energy.
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A coil of wire is placed in a magnetic field. If the magnetic field is increased, what will happen to the current in the coil?
(A) The current will increase.
(B) The current will decrease.
(C) The current will stay the same. -
A generator is a device that converts mechanical energy into electrical energy. How does a generator work?
(A) A generator uses a rotating magnetic field to induce an electric current in a coil of wire.
(B) A generator uses a stationary magnetic field to induce an electric current in a coil of wire.
(C) A generator uses a combination of a rotating and a stationary magnetic field to induce an electric current in a coil of wire. -
A transformer is a device that transfers electrical energy from one circuit to another. How does a transformer work?
(A) A transformer uses a magnetic field to induce an electric current in a coil of wire.
(B) A transformer uses a rotating magnetic field to induce an electric current in a coil of wire.
(C) A transformer uses a combination of a rotating and a stationary magnetic field to induce an electric current in a coil of wire. -
What is the principle of electromagnetic induction?
(A) When a conductor is placed in a changing magnetic field, an electric current is induced in the conductor.
(B) When a conductor is placed in a static magnetic field, an electric current is induced in the conductor.
(C) When a conductor is moved through a magnetic field, an electric current is induced in the conductor. -
What is the difference between direct current (DC) and alternating current (AC)?
(A) DC is a type of current that flows in one direction, while AC is a type of current that flows in both directions.
(B) DC is a type of current that has a higher voltage than AC.
(C) DC is a type of current that has a lower frequency than AC. -
What is the purpose of a rectifier?
(A) A rectifier is a device that converts AC to DC.
(B) A rectifier is a device that converts DC to AC.
(C) A rectifier is a device that converts AC to a higher voltage. -
What is the purpose of an inverter?
(A) An inverter is a device that converts DC to AC.
(B) An inverter is a device that converts AC to DC.
(C) An inverter is a device that converts AC to a higher voltage. -
What is the purpose of a capacitor?
(A) A capacitor is a device that stores electrical energy.
(B) A capacitor is a device that conducts electricity.
(C) A capacitor is a device that blocks electricity. -
What is the purpose of an inductor?
(A) An inductor is a device that stores electrical energy.
(B) An inductor is a device that conducts electricity.
(C) An inductor is a device that blocks electricity. -
What is the purpose of a resistor?
(A) A resistor is a device that converts electrical energy into heat.
(B) A resistor is a device that conducts electricity.
(C) A resistor is a device that blocks electricity.