ELECTROMAGNETIC INDUCTION
When there is a change in the number of magnetic lines of force linked with a coil, an induced emf is developed in the coil. The phenomenon is known as electromagnetic induction.

⭐ emf - electro motive force

Three results of Faraday’s Experiment on electromagnetic induction:
➡️ when there is a change in the number of magnetic lines of force linking with a coil, an induced emf is set up in the coil
➡️ induced current in the coil lasts only as long as there is change in the number of forces linking with the coil
➡️ the strength of induced emf is directly proportional to the rate of change of magnetic lines of force linked with the coil.

⭐ Change in the number of magnetic lines of force linked with the coil is the basic cause to induce an emf in a coil.

Two different ways to induce current in a coil: ➡️ Current is induced in the coil when a magnet is moved relative to the fixed coil.
➡️ Current is also induced in the coil when it is moved relative to a fixed magnet.

The direction of induced current in the coil depends on the direction of magnetic field and direction of motion of the coil/conductor. It is given by Fleming’s Right Hand Rule.

Fleming’s Right Hand Rule:

It states that if the forefinger, the middle finger and the thumb of the right hand are stretched mutually perpendicular to each other such that the forefinger points in the direction of magnetic field and the thumb points in the motion of the conductor then the middle finger indicates the direction of the induced current in the conductor.

Types of Current: ➡️ Alternating current (AC): If the current changes its direction periodically, then it is called an Alternating Current (AC).
➡️ Direct Current (DC): If the current flows in one direction only, then it is called Direct Current (DC).

Generator or Dynamo or Alternator: It is a device which is used to generate electricity by converting mechanical energy into electrical energy.

Basic Principle of Electromagnetic induction: Electric generator works on the principle that whenever there is a relative motion between a coil and a magnet, an induced current is developed in the coil.

Types of Generators: AC Generator: A device that converts mechanical energy into electrical energy in the form of alternating current.



Construction: AC generator consists of the following parts:
👉🏽 Armature
👉🏽 Field Magnet
👉🏽 Slip rings
👉🏽 Brushes

⭐ Slip rings: Two metallic rings R1 and R2 which are connected to the ends of the armature coil and rotate along with the coil about the same axis.

Working: At start, let the plane of the armature coil be perpendicular to the magnetic field as shown in the figure. Here, maximum numbers of magnetic lines of force passes through the plane of the coil but no induced current is developed as the coil is at rest. Now, let the coil be rotated in anti-clockwise direction in which arm AB moves downward while arm CD comes upward. Due to change of magnetic lines of force linked with the coil, induced current is developed in the coil. According to Fleming’s Right Hand Rule, induced current flows from B to A and D to C in the arms AB and CD respectively. In the external circuit, current flow from B1 to B2.

After half-rotation of the coil, the plane of the coil retains its vertical position with arm AB below CD. As the coil rotates further in the same direction, induced current is developed in the coil. Again, according to Fleming’s Right Hand Rule, current flows from A to B and C to D in the arms AB and CD respectively. In the external circuit, current flows from B2 to B1. This cycle is repeated as the coil contains its rotational motion, and the current produced changes its direction periodically. Thus, the alternatively current AC is generated.

DC Generator: It is a device that converts mechanical into electric energy in the form of DC current.



Construction: DC generator consists of the following parts:
👉🏽 Armature
👉🏽 Field Magnet
👉🏽 Slip rings
👉🏽 Brushes

❓Define the term Frequency of AC source?
In a second, the number of times the current flows in a given direction is known as frequency of the AC source. It is also given by the number of complete cycles in one second.
The SI unit of frequency is Hertz (Hz).
In household supply, the frequency of AC is 50 Hz. It means that the AC source has 50 complete cycles in one second and therefore, current changes its direction 100 times in one second.

Difference between AC and DC:

AC	DC
1. Current changes its direction periodically.	1. Current flows in one direction only.
2. The frequency of the AC is desirable/ can be set at any level.	2. The frequency of DC is zero DC has no frequency.
3. The voltage of AC can be stepped up or stepped down with the help of a transformer.	3. The voltage of Dc cannot be changed.

Difference between AC Generator and DC Generator:

AC Generator	DC Generator
1. AC generator produces AC in which current changes its direction periodically.	1. DC generator produces direct current in which flows in one direction only.
2. In AC generator two slip rings are used.	2. In DC generator only one slip ring is used.
3. In AC generator the two slip rings are in contact with the two brushes constantly and separately.	3. In DC generator the two half rings are in contact with the two brushes alternately in the right time.

Advantages of AC over DC: ➡️ AC can be converted into DC more easily, which DC cannot be converted into AC
➡️ The voltage of AC can be increased or decreased, while that of DC cannot be changed
➡️ AC can be transmitted to distant places without much loss of energy, whereas DC cannot be used in distant transmission of electricity.

❓What is the nature of current used in distant transmission of electricity? Why?
AC at high voltage, low current nature. It is because this nature of current can minimize the loss of energy due to heating effect in distant transmission of electricity.

Graphical representation of the variation of emf:

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⭐ Function of Brushes: To give electrical connection between the source of electricity, i.e.; battery and the rotating armature coil.

Induction for deduction, with a view to construction
- Auguste Comte