Understanding Magnetic Fields: Properties, Generation, and Applications
Magnetic Field
A magnetic field is a region around an electric current or magnetic substance where magnetic phenomena (attraction, repulsion) are observable.
Its shape can be visualized by sprinkling iron filings on a sheet of cardboard placed over a magnet. The filings align along lines indicating the field’s direction and strength, known as lines of induction or magnetic field lines.
A line of force represents the path an imaginary north pole would follow under the influence of the magnetic field, effectively mapping the field’s direction. The direction is from North to South outside the magnet.
Magnetic Field Magnitude
The magnetic field’s strength is quantified by magnetic induction or flux density, a vector quantity dependent on the medium. Magnetic induction is tangent to the lines of force. Units of measurement include Tesla (T) in the SI system and Gauss (G), where 1 T = 10,000 G.
Electromagnetic Field Generated by a Straight Current
The field has a cylindrical shape, with lines of force concentric with the current.
Magnetic Flux
Magnetic flux measures the number of magnetic field lines passing through a closed surface “S” within a magnetic field of value “B”. More lines indicate increased flux strength. Units: Weber (Wb) in SI, Maxwell (Mx).
Electric Power Generation
Electric power generation involves generating electromotive force (EMF) using a magnet and a coil. An elementary generator consists of a magnet, a coil, and relative movement between them (translation or rotation).
Principle of Electromagnetic Induction
When a coil is subjected to a changing magnetic flux, it generates an induced EMF that opposes the change causing it.
Variation of Flux
- Inductor element motion, translation, or rotation (alternator).
- Changing current in the inductor (current transformer).
Applications
- Generation of electric current: alternator, dynamo.
- Transformation of electric current, voltage transformation.
- Speed sensor.
- Pulse generator.
Electromagnetic Induction
An electromagnet generates a magnetic field. Its rotation causes a change in flux in the armature coils, generating AC voltage in each phase.
Self-Induction
A coil carrying a variable current generates a variable magnetic field, which in turn induces a variable magnetic flux within the coil itself. This leads to a self-induced electromotive force that opposes the change in current.
When a switch is opened or closed in a DC circuit containing a coil, the current briefly varies from zero to a constant value or vice versa. During these periods, an EMF is generated.
Transformers
A transformer consists of two coils wound around the same iron core. The coil where voltage is applied is called the primary coil, and the coil where voltage is induced is called the secondary coil.
Generation of Movement
The action of a magnetic field “B” on a straight current “I” subjects the current to a force.
The direction of this force can be determined using the left-hand rule.