Notes of Chap 13
Magnetic Effect of Electric Current
- Introduction
- Properties of Magnet
- Magnetic field and field lines
- Magnetic Field Due to A Current Carrying Conductor
- Magnetic Field Due to A Current Through a Straight Conductor
- Right-Hand Thumb Rule
- Magnetic Field Due to A Current Through a Circular Loop
- Magnetic Field Due to a Current in a Solenoid
- Force On A Current-Carrying Conductor In A Magnetic Field
- Fleming's Left-Hand Rule
- Electric Motor
- Electromagnetic Induction
- Fleming's Right-Hand rule
- Galvanometer
- Electric Generator
- Domestic Electric Circuits
Introduction:
Magnet: An Object that attracts iron or iron-like substance and produces a magnetic field around it is called a magnet.
Types of Magnet There are three types of magnet:- (i) Temporary Magnet (ii) Permanent Magnet (iii) Electromagnets
(i) Temporary Magnet: The substance that becomes a magnet in presence of magnetic field and loss their magnetism after removing magnetic field is called temporary magnet.e.g- Iron and Iron alloy objects like a screwdriver, hairpins, etc.
(ii) Permanent Magnet: The substance that doesn't lose their magnetism easily and occurring naturally is called permanent example: Nickel Cobalt magnet
(iii) Electromagnets: The substance which becomes a magnet in the presence of electric current and loss their magnetism after removing the electric current is called electromagnets.
Electromagnetic Crane
Properties of Magnet:
(i) Every magnet in the universe has two poles the North Pole and the South Pole.
(ii) Unlike poles of a magnet attract each other.
(iii) Like poles of a magnet repel each other.
(iv) A freely suspended magnet always points the two directions North and the South Pole.
Magnetic field and field lines:
Magnetic field: A region around the magnet where magnetism can be detected is called the magnetic field. It is denoted by symbol "B". The S.I unit of the magnetic field is "Tesla".
Magnetic field line: An imaginary line around the magnet that gives us the direction of magnetic field strength from the North Pole to South pole is called the magnetic field line.
Properties of the magnetic field line:
- The magnetic field line never intersects with each other at any point.
- The magnetic field line always parallels to each other.
- The magnetic field line always directed from the North Pole towards the South Pole.
- The magnetic field lines always form a closed loop.
- The magnetic field line is much denser near the magnet while less dense than the magnet.
Magnetic Field Due to A Current Carrying Conductor :
All current-carrying conductor produces magnetic fields. When we flow electric current through it. The magnetic field can be detected by placing a compass close to the wire. To finding the direction of the magnetic field we will use SNOW rule.
SNOW Rule: This rule states that if the electric current is flowing in an electrical circuit from South direction to North direction and a compass is placed Over the conducting wire, then the needle of the compass deflects within the direction of the west.
Note: If the electric current is flowing in an electrical circuit from North to South then the magnetic field will also get changed and compass middle deflected in the direction of the east.
Magnetic Field Due to A Current Through a Straight Conductor :
When we flow electric current through the straight conductor then it produces a magnetic field around the whole wire in the pattern of concentric circles. We can easily find the direction of the magnetic field line by using "Right-Hand Thumb Rule".
Note: If the direction of current is outside to inside then the magnetic field line direction will be clockwise. If the direction of current will be inside to outside then the magnetic field line direction will be anticlockwise.
Right-Hand Thumb Rule :
Right-Hand Thumb Rule: According to this rule if we placed our right-hand thumb in the direction of electric current then our remaining four wrapped a finger around the wire give us the direction of the magnetic field line.
Note: This rule is used to find the direction of the magnetic field line around any current-carrying conductor or wire.
Magnetic Field Due to A Current Through a Circular Loop:
As we already read about that a straight current-carrying conductor produces a magnetic field around it. When we bent straight current-carrying conductor into a circular loop then the magnetic field produced by the conductor is in the same direction at every point of the circular loop. Because Current flowing in the circular loop is one-directional.
Note- 1. The magnetic field is directly proportional to the current passing through the conductor.
2. The magnetic field is inversely proportional to the distance from the current-carrying conductor.
3. The magnetic field is directly proportional to the strength of the flowing current through the conductor.
4. Around the circular loop, concentric circles represent the magnetic field.
5. Concentric circles get larger and larger as we move away from the conductor.
Magnetic Field Due to a Current in a Solenoid:
Solenoid: A group of many circular loops of the coil which form a cylindrical shape and act as the magnet when the electric current passing through it is known as a solenoid.
Solenoid works similarly as a bar magnet.
Solenoid gives us the direction of poles as a bar magnet.
In solenoid magnetic field line arises from the north pole and meet at the South pole of the solenoid.
The magnetic field inside a long straight solenoid has the same at every point.
When we put an iron rod inside the solenoid then the strength of the magnetic field gets increased.
Force On A Current-Carrying Conductor In A Magnetic Field:
Whenever we place a current-carrying conductor in a magnetic field then a force act on the conductor due to the magnetic field. Scientist Andre Marie Ampere suggested that the magnet also exert force on the current-carrying conductor.
Note: The maximum displacement occurs when the current passing through the conductor at the 90° angle with the magnet.
To find the force direction due to the magnetic field we use the "Fleming's Left-Hand Rule".
Fleming's Left-Hand Rule:
Fleming's Left-Hand Rule: The simple rule in which we stretch our left-hand thumb, forefinger and middle finger perpendicularly to each other then thumb Indicate the direction of motion/force, forefinger Indicate the magnetic field and the middle finger Indicate the current. this simple rule is known as Fleming's Left Hand Rule.
Note: This rule is used to find the direction of produced force/movements due to the magnetic field around the magnet.
MRI(Magnetic Resonance Imaging): We know that an electric current always produces a magnetic field. Two main organs in the human body where the magnetic field produced are significant are the heart and the brain. The magnetic field inside the body forms the basis of obtaining images of different body parts. This is done using a technique called MRI(Magnetic Resonance Imaging).
Electric Motor:
Electric Motor: A rotating device that converts electrical energy to mechanical energy is called electric motor. It is used to make a fan, cooler, etc.
Principle and working of an electric motor: Electric Motor is based on the magnetic effect of electric current principle. When we placed an insulated coil ABCD inside the magnetic field between the North and the South Pole then it experiences a force that is due to the magnetic field.
Where the arm of coil AB and CD is perpendicular to the direction of the magnetic field. The end of the coil is connected to the two halves P and Q of the split ring. The inner side of the halves is insulated and attached to an axle. The external conducting edges P and Q touch two stationary brushes X and Y respectively as shown in the above figure.
On applying a current through the brush X it passes through A to B, B to C and C to D then current flow back to another brush Y. On applying Fleming's Left-Hand Rule we show that a force act on AB in Downward direction. While CD pushes it in an upward direction. Thus the coil and the axle O mounted free to turn about an axis, rotate anti-clockwise. The same thing happens when we change the direction of electric current in the motor but the direction of rotation gets changed to clockwise direction. That's the working of an electric motor.
Components of the electric motor:
Armature: The rotating coil inside the electric motor or dynamo which is wounded on the soft iron core is called the armature.
Coil: A thin wire mounted on the axle inside the motor or dynamo is called a coil.
Axle: A spherical rod inside the armature is called an axle.
Commutator: A device that connects the coil to the electric current source is called the commutator.
Split ring: It is the type of commutator which is used to reverse the direction of current in electric motor or DC generator.
Slip ring: It is also a type of commutator which is used to keep maintain the connection between the moving rotor and stationary stator in electric motor or AC generator.
Brush: A part of the motor or generator which conducts current between a stationary wire and rotatory wire.
Electromagnetic Induction:
Electromagnetic Induction: The phenomenon of inducing current inside the magnetic field due to the movement of the conductor is called electromagnetic induction.
Induced current: The flowing of electrons on the conductor due to movement of conductor inside the magnetic field is called induced current.
When we move magnet inward: Deflection can be seen in Galvanometer.
When we put a magnet inside still: Deflection can not be seen in Galvanometer.
When we withdraw magnet from inside: Deflection can be seen in Galvanometer.
Hence, We can say that without movement of conductor or magnet Induce current can't be generated.
Note: We can find the direction of Induce current by using "Fleming's Right Hand Rule".
Fleming's Right-Hand Rule:
Fleming's Right-Hand Rule: The simple rule in which we stretch our right-hand thumb, forefinger, and middle finger perpendicularly to each other then thumb Indicate the direction of motion of conductor, forefinger Indicate the magnetic field and the middle finger Indicate the induced current. this simple rule is known as Fleming's Right Hand Rule.
Note: This rule is used to find the direction of Induced current in electromagnetic induction.
Galvanometer:
Galvanometer: A device that is used to
detect the presence of electric current in a conductor or electric circuit is called a galvanometer.
Electric Generator:
Electric Generator: A rotating device that converts mechanical energy to electrical energy is called an electric generator. It is used to generate electricity in our homes or in many places.
Principle and working of electric AC generator: Electric Generator is based on the electromagnetic induction principle.
Placed a Coil ABCD between the two poles of the permanent magnet. The two ends of this coil are connected to the two Slip rings R₁ and R₂. The two conducting stationary brushes B₁ and B₂ kept pressed separately on the slip rings R₁ and R₂ respectively.
These slip rings are internally attached to an axle. If you rotate axle in a clockwise direction then the Induced current direction will be inward B₁ to outward B₂ but after half rotation, it's polarity get changed thus the Induced current direction will also be changed.
You can also verify this Induced current direction by using Fleming's Right Hand Rule. If you change the rotational direction of the axle then the Induced current direction will also change from B₂ to B₁. This is the working principle of the Electric Generator.
By this Slip rings, we can obtain AC Current whose current direction regularly gets changed.
DC generator: If you want to make DC Generator then used Split rings instead of slip rings that keep maintaining the direction of current in brushes always.
AC (Alternate Current): The current which changes their direction periodically is called alternate current. Its frequency in India is 50Hz and the potential difference between a live wire and the neutral wire is 220V.
It can be transmitted easily over a long distance without losing much energy but it can't be stored.
DC (Direct Current): The current which doesn't change their direction periodically is called Direct current. It loses much energy during the transmission of this current but it can be stored easily.
Domestic Electric Circuits:
Domestic Circuit: The circuit which is normally used in our home is called the domestic circuit.
Types of wire used in the domestic circuit: Generally three types of wire used in the domestic circuit:- (i) Live wire (ii) Neutral wire (iii) Earth wire
Live wire: The wire which carries a positive charge is called live wire. It is indicated by the red insulated cover.
Neutral wire: The wire which carries a negative charge is called neutral wire. It is indicated by the black insulated cover.
Earth wire: The wire which protects us from the current leakage/short circuit is called earth wire. It is indicated by the green insulated cover.
Structure of domestic circuit: Pole → Fuse → Electricity meter → Main Board → Distribution box → To sperate as requirements
Short circuit: When live wire and neutral wire contacts accidentally to each other then the resistance of wire gets decreased and the amount of current flow through the wire becomes high that causes a short circuit.
Overloading: Flowing of current by conductor more than the wire capacity is called overloading.
Safety device: The device which protects us from a short circuit in the electric circuit is called a safety device.
Examples of safety devices: Fuse, MCB(Miniature Circuit Breaker), Earth wire.
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