Magnet:
A magnet is substance or object that has property to attract magnetic materials. A magnet has following properties:
- It has two poles north and south poles. It is assumed that magnetic particles have north and south poles.
- Unlike poles attracts and like pole repel each other
- It stays in south and north direction while hanged with strength
- Magnetic core is induced in any attached magnetic materials.
- The poles never separate from each other in a particle of magnet
- Natural magnet is known as load stone. Artificial magnet are made by alloys which is made up of generally Aluminum, Nickel
Magnet are very useful in our daily life we can use it to separate iron pieces from any mixer .e.g. bar magnet, horse shoe magnet, circular magnet.
Magnetism
An attractive and repulsive phenomena caused by a moving electric charge is known as magnetism. Both an electric and a magnet field are present in the area that is affected by a moving charge. The electromagnetic force is moving electric charge produce by magnetism.
Types of magnet
- Temporary magnet
Temporary magnets can be magnetized in the presence of a magnetic field. When the magnetic field is removed, these materials lose their magnetic property. Some iron and iron alloys act as temporary magnets, as well as paper clips and nails. - Permanent magnet
Permanent magnets are those magnets that are commonly used. They do not lose their magnetic property once they are magnetized so they are known as permanent magnet.
- Electro magnet
Electromagnets consist of a coil of wire wrapped around a metal core made from iron. When this material is exposed to an electric current, a magnetic field is generated, making the material behave like a magnet. The strength of the magnetic field can be controlled by controlling the electric current.
Magnetic and non-magnetic materials
Magnetic materials
The materials that can get attracted to the magnets are called Magnetic materials. Examples:- Nickel, Cobalt, Iron and Steel. Magnetic materials can be magnetized.
- Dia-magnetic substance:
The substance that are repelled by the magnet are known as dia-magnetic substance. For eg, gold, silver, etc. - para-magnetic substance:
The substance that are weakly attracted by the magnet are known as para-magnetic substance. For eg: Aluminum, platinum, etc. - Ferro-magnetic substance:
The substance that are strongly attracted by the magnet are known as ferro-magnetic substance. For eg: iron, steel etc.
Non magnetic materials
The materials that do not get attracted to the magnets are called Non-magnetic materials. Examples:- Wood, Plastic, Rubber, Copper, etc. Magnetic materials cannot be magnetized
Introduction to magnetic terminologies
- Magnetic field
It is a vector field that describes the magnetic influence on moving electric charges, electric current and magnetic materials .
- Magnetic field intensity
The Magnetic Field Intensity or Magnetic Field Strength is a ratio of the MMF needed to create a certain flux density (B) within a particular material per unit length of that material. Magnetic field intensity (H) at any point in the magnetic field is defined as the force experienced by the unit north pole at that point. In simple terms, it is a measure of how strong or weak any magnetic field is. The SI unit of magnetic field intensity is Ampere/meter (A/m).
magnetic flux
The total no of force produced in any magnetic field is known as magnetic flux. It is denoted by Φ, and its SI unit is weber (W b). The more the magnetic lines of force, the more the magnetic flux, hence the more stronger magnetic field.
Magnetic flux density
The total no of magnetic lines of force through units surface area (A) normally (being perpendicular) is known as a magnetic flux density. It is denoted by ’B’ and its SI unit is Tesla.
Formula:
Magnetic flux density (B) = Magnetic flux/Area
B = Φ/A
= wb /m 2(Tesla)
Magnetic effect of current
An electric current flowing in wire produces a magnetic field around it. E.g. when a compass is brought near a current carrying conductor the needle of compass gets deflected because of flow of electricity.
Application
Electric bells and motors – Loudspeakers – Electric fans – Toys and telephone instruments, etc.
Electric motors, which are used in a wide range of devices from electric cars to household appliances. In an electric motor, a current is passed through a coil of wire, creating a magnetic field. This interacts with another magnetic field, causing the coil to rotate and drive the motor. Understanding the basics of the magnetic field can provide deeper insights into how these interactions work.
Transformers, another application of the magnetic effect of currents, are used to change the voltage of alternating current (AC). They consist of two coils of wire wrapped around a common iron core. When an AC current is applied to one coil, it creates a changing magnetic field in the core, which induces a current in the second coil. By changing the number of turns in each coil, the voltage can be stepped up or down. The process of electromagnetic induction is crucial for the operation of transformers.
Magnetic Resonance Imaging (MRI) machines use a strong magnetic field to align the protons in the body’s hydrogen atoms. A radio frequency current is then applied, causing the protons to spin out of alignment. When the current is turned off, the protons realign and emit a radio signal, which is used to create detailed images of the body’s internal structures. This non-invasive technique has revolutionised the field of medical diagnostics. For a deeper understanding of the forces between current-carrying wires in such technologies, exploring forces between current-carrying wires can be enlightening.
Principle of electromagnetism
Electromagnetism:
Electromagnetism is a fundamental branch of physics that deals with the study of electric and magnetic fields and their interactions with matter. The principles of electromagnetism are described by Maxwell’s equations, which unify the concepts of electricity and magnetism into a single coherent theory. Electric charges generate electric fields. The force between two charges is described by Coulomb’s Law. An electric field (E) exerts a force on other charges within the field, with the force proportional to the charge and the strength of the electric field. A changing electric field generates a magnetic field and vice versa. This interplay allows for the propagation of electromagnetic waves, such as light, through space. Maxwell’s equations predict the existence of these waves and their speed (the speed of light).
Electromagnet:
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. When an electric current flows through a coil of wire, it generates a magnetic field. The strength of this field is proportional to the current and the number of turns in the coil. Placing a ferromagnetic core (like iron) inside the coil amplifies the magnetic field. The core material increases the magnetic field strength because it becomes magnetized by the current. The magnetic field of an electromagnet can be switched on and off by controlling the electric current. When the current stops, the magnetic field disappears
Electromagnetic Induction
Electromagnetic Induction is a current produced because of voltage production (electromotive force) due to a changing magnetic field. This either happens when a conductor is placed in a moving magnetic field (when using an AC power source) or when a conductor is constantly moving in a stationary magnetic field.
Fraday’s experiment
Michael Faraday’s experiments in the early 19th century demonstrated the fundamental principle of electromagnetic induction, which is the generation of an electric current by changing magnetic fields. One of his classic experiments involved using a galvanometer, a coil of wire, and a magnet. The coil is connected to the galvanometer. The magnet is initially at rest, far from the coil, so no current is observed in the galvanometer.
When the magnet is moved towards the coil, the magnetic field through the coil changes. This changing magnetic field induces an electromotive force (EMF) in the coil according to Faraday’s Law of Induction. The galvanometer detects a current, indicating the presence of induced EMF.
If the magnet is held stationary near the coil, the magnetic field through the coil becomes constant. No change in the magnetic field means no induced EMF, and the galvanometer shows no current. When the magnet is moved away from the coil, the magnetic field through the coil changes again, but in the opposite direction.
This change induces an EMF in the opposite direction, and the galvanometer detects a current flowing in the opposite direction. The galvanometer needle deflects when the magnet is moved towards or away from the coil, indicating an induced current.
The direction of the induced current depends on the direction of the magnet’s motion. Moving the magnet towards the coil induces current in one direction, while moving it away induces current in the opposite direction. The speed of the magnet’s movement affects the magnitude of the induced current. Faster movement results in a greater change in magnetic field and a stronger induced current.
Faraday’s Law of Electromagnetic Induction
First Law:
Whenever the number of magnetic lines of force (flux) linking with a coil or circuit changes, an emf gets induced in that coil or circuit.
Second Law:
The magnitude of the induced emf is directly proportional to the rate of change of flux linkage (flux*turns of coil).
e= -N* (d/dt) volt.
According to Faraday’s law of electromagnetic induction, when a conductor travels within a magnetic field, a current is induced in it. The direction of the applied force, magnetic field, and current will all be correlated if this conductor is forcefully shifted inside a magnetic field.
Lenz’s Law:
This rule is based on the principles derived by German Physicist Heinrich Lenz According to Lenz’s law, “An induced emf generated by electromagnetic induction is such that it sets up a current which always opposes the cause that is responsible for generating the emf”. In other words, the induced emf always opposes the cause that produces it, which is denoted mathematically by a negative sign.
E = -N* (d/dt) volt.
Where,
E – Induced emf
d – Change in magnetic flux
N – No. of turns of coil
Types of Induced emf
Dynamically Induced e.m.f.:
The term “dynamically induced emf” or “motional induced emf” refers to an induced emf that results from the physical movement of a conductor or coil with regard to flux or from the movement of a magnet with respect to a stationary conductor or coil. It can occur in two cases:
1. When conductor is moving in stationary magnetic field.
2. Or moving the entire field system while keeping the conductor stationary. In both the above cases magnetic flux is cut by the conductor to induce emf in the Conductor.
Statically Induced e.m.f:
Without physically changing the coil or the magnet, it is possible to modify the flux lines with respect to coil. The term “statically induced emf” refers to an induced emf in coil that doesn’t involve any physical movement of the coil or a magnet.
Self-Induced EMF:
Self-induced EMF is the EMF induced in a circuit due to the change in its own magnetic flux. When the current flowing through a coil or circuit changes, it alters the magnetic field generated by the coil. This changing magnetic field, in turn, changes the magnetic flux through the coil itself. According to Faraday’s Law of Induction, this change in magnetic flux induces an EMF within the same circuit.
The magnitude of self-induced emf(e)= N* (d/dt) .
Mutually Induced EMF:
Mutually induced EMF is the EMF induced in one circuit due to the change in magnetic flux caused by a changing current in a nearby circuit. When current changes in a primary coil, it changes the magnetic field around it. This changing magnetic field affects the magnetic flux through a secondary coil placed nearby. According to Faraday’s Law of Induction, this change in magnetic flux through the secondary coil induces an EMF in the secondary coil. The magnitude of mutually-induced emf(e)= Nm* (d/dt) .
Characteristics of mutually induced emf
– The magnitude of mutually-induced emf(e)= Nm* (d/dt) .
– In accordance with lenz’s rule, mutually induced emf tends to resist cause of its induction. Due to mutually induced emf, the induced current in coil B will flow in a direction that links Coils A and B.
– Mutual inductance is the property of two coils that allows voltage to be generated in one coil by altering current in the other.
– As long as the current in a coil A is changing, mutually induced emf in coil B will continue to exist. When the current density in coil A reaches a fixed value, the mutual flux stops fluctuating and the mutually induced emf drops to zero.