FSc ICS Notes Physics XII Short Questions & Definitions Chapter 15 Electromagnetic Induction

FSc ICS Notes Physics XII Short Questions & Definitions Chapter 15 Electromagnetic Induction 2nd Year Physics Notes Online Taleem Ilmi Hub

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Induced emf: The emf produced in the conductor is called induced emf, when a moving conductor is kept moving in the magnetic field.

Induced current: Electric current in a conductor caused by emf set by a changing magnetic field surrounding it.

Electromagnetic induction: The process by which an emf is set in a conductor located in a magnetic field, when the magnetic flux is cut by the conductor.

Magnetic flux: Lines of force in a magnetic field considered collectively.

Electromagnet: A coil of wire wrapped around a core of soft iron. When there is a current in the wire, a magnetic field results; the core becomes magnetized. The core loses its magnetism when the current is switched off. Electromagnets are used in telephones, electric bells, etc.

Permanent magnet: A sample of a substance that retains its magnetism when the external magnetic field is removed.

Temporary magnet: The substance whose magnetism disappears as soon as the inducing field is removed.

Motional emf: The producing of a potential difference when a conductor is moved across a magnetic field.

Electric intensity (or Electric field intensity): The force experienced by a unit positive charge placed at that point in an electric field.

Potential gradient: The change in potential per unit distance.

Faraday’s law of electromagnetic induction:

• The average emf induced in a conducting coil of n loops is equal to the negative of the rate at which the magnetic flux through the coil is changing with time.
• An electromotive force is induced in a conductor when there is a change in the magnetic field around it.
• The electromotive force induced is proportional to the rate of change of the field.

Lenz’s law: The direction of the induced current is always such as to oppose the cause which  produces it.

Drag: To pull by force or draw along slowly and heavily.

Law of conservation of energy: The total energy of a system cannot change unless energy is taken from or given to the outside. The law is equivalent to the first law of thermodynamics.

Perpetuate: Continue indefinitely or extend without interruption; to make everlasting.

Magnetic flux: Lines of force in a magnetic field considered collectively.

Mutual induction: The mutual action of the magnetic fields of the primary and secondary coil, or circuits, resulting an induced emf in the secondary.

Mutual inductance: It is the property of mutual induction of the two circuits.

Henry (H): The SI unit of inductance, equal to the inductance of a closed circuit that has a magnetic flux of one Weber per ampere of current in the circuit.

Self induction: The production of an emf in a conductor or coil caused by changes in the current in the conductor (or coil) itself.

Self induced emf: If a magnetic flux is produced through a coil due to current in it. Then changes in the magnetic flux producing an induced emf, called self induced emf.

Self inductance: The property of self induction possessed by a coil; it is also called electromagnetic inertia.

Core (or Core material): A length of soft iron forming the centre of an electromagnet or an induction coil.

Para magnetism: The property of a substance by which it is feebly attracted by a strong magnet.

Diamagnetism: The property of a substance whereby it is feebly repelled by a strong magnet.

Ferromagnetism: The property of a substance by which it is strongly attracted by a magnet.

Ferromagnetic material: The material which contains the property of ferromagnetism.

Rheostat: A variable resistor for regulating electric current.

Back emf: An emf that opposes the normal flow of electric charge in a circuit or circuit element.

Inductor (or Reactance coil): A coil or other piece of apparatus, possessing inductance and selected for use because of that property.

Inductance: A property of an electric circuit that results from the magnetic field set up when a current flows.

Capacitor: A combination of conducting plates separated by an insulator and used to store an electric charge.

Ammeter: A meter used to measure electric current.

Current generator: An electromechanical device that converts mechanical energy into electrical energy.

Alternating current generator: A generator in which the coil connected with two slip rings is rotated by some means in a uniform magnetic field produce an induced emf, which causes an alternating current.

Direct current generator: A generator in which the coil connected with two commutators is rotated by some means in a uniform magnetic field produce an emf, which causes one-directional current.

Commutator:

• A device for reversing the direction of the current in an electric circuit or in some part of a circuit.
• The part of a direct current generator that connects the coil to the outside circuit, changing the connections round as the coil rotates.

Faraday’s law of electromagnetic induction: The electromotive force induced is proportional to the rate of change of the magnetic field around it; E = -N (Δφ / Δ t)

Slip ring (or Collector ring): A ring, usually made of copper, that is connected to and rotates with a winding, so that the winding may be connected to an external circuit by means of a brush or brushes resting on the surface of the ring.

Concentric: Having a common center, as circles.

Carbon brushes: An electrical contact with a moving part, as on a generator.

Alternating current: An electric current, which has one direction during one part of a generating cycle and the opposite direction during the remainder of the cycle.

Direct current: A current in which the movement of electrons is in one direction only.

Turbine: An engine in which a shaft is rotated by fluid impinging upon a system of blades or buckets mounted upon it.

Steam turbine: Steam engine in which steam drives a rotor.

Alternating current generator: A generator in which the coil connected with two slip rings is rotated by some means in a uniform magnetic field produce an induced emf, which causes an alternating current.

Homopolar generator: In 1831 Michael Faraday discovered it. A copper disc was secured to a cylindrical magnet with paper intervening the two. The poles of the magnet were aligned along the axis of the copper disc. Wires of a galvanometer brushed the center and circumference of the copper. Upon rotation of the copper disc and magnet, an emf was created between the terminals of the galvanometer.

Motor: A machine that does work mechanically when it is driven by an electric current.

D.C. motor: A machine that does work mechanically when it is driven by direct current; Reverse of D.C generator.

D.C.generator: A generator in which the coil connected with two commutators is rotated by some means in a uniform magnetic field produce an emf, which causes one-directional current.

Slip rings: Parts used in an A.C. generator. These are concentric with the axis of the loop and rotate with it.

Split rings: These are two halves of a ring that act as a commutator.

Shaft: Anything shaped like an arrow, as the stalk of a plant or broken handle of a cricket bat.

Turbine: An engine in which a shaft is rotated by fluid impinging upon a system of blades or buckets mounted upon it.

Load: The devices in the circuit of the generator that consume electrical energy.

Motor: The machine which converts electrical energy into mechanical energy.

Dynamo: A small electric generator for converting mechanical energy into electrical energy.

Commutator: The part of a direct current generator that connects the coil to the outside circuit, changing the connections round as the coil rotates.

Armature (or Rotor): A coil of wire formed around an iron or steel core, which rotates in the magnetic field of a generator or motor.

Field coil: A coil that, when carrying a current, magnetizes a field magnet of an electrical machine (dynamo or inductor).

Armature coils: Coil of wires formed around an iron or steel core, which rotates in the magnetic field of a generator or motor.

Back emf: An emf that opposes the normal flow of electric charge in a circuit or circuit element.

Transformer: A device for changing an alternating voltage from a low potential to a high potential or vice versa.

Mutual induction: The mutual action of the magnetic fields of the primary and secondary coil, or circuits, resulting an induced emf in the secondary.

Primary: In a transformer or induction coil, the input winding that carries current and normally induces a current in one or more secondary windings.

Secondary: In a transformer or induction coil, the output winding in which the current is due to inductive coupling with another winding called the primary.

Step up transformer: A transformer for increasing an alternating voltage.

Step down transformer: A transformer for reducing alternating voltage.

Eddy currents:

• Closed loops of induced current circulating in plates perpendicular to the magnetic flux.
• Currents induced in the structure of an electric machine.

Magnetic hysteresis: The lagging of magnetization of ferromagnetic material behind the magnetizing force.

Hysteresis loop: The loop formed by magnetic hysteresis.

Written By: Asad Hussain