FSc ICS Notes Physics XII Short Questions & Definitions Chapter 14 Electromagnetism 2nd Year Physics Notes Online Taleem Ilmi Hub
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Electromagnetism: The study of electricity and magnetism with inter related phenomena.Electric current: The rate of flow or charge past a given point in an electric circuit.
Magnetic field: The region or space near a magnet where the effects of magnetism such as the deflection of a compass needle can be detected.
Compass needle (or Magnetic compass) : A device used to show magnetic force field direction.
Right hand rule: If the wire is grasped in the right hand with the thumb pointing in the direction of the current, the fingers of the right hand will circle the wire in the direction of the magnetic field.
Magnetic induction: The production of magnetic order in a material by an external magnetic field.
Tesla: The SI unit of magnetic flux density, equal to a flux density of one weber of magnetic flux per square meter. 1 T = 1 Wb m-2 .
Extension of right hand rule: First determine the field around the conductor carrying the current. The conductor always experiences a force directed from the region where the two fields reinforce each other to the region where they cancel. Rotate the current carrying conductor so that the direction of flow of current coincides with the direction of magnetic field. The direction of rotation should be that in which the angle of rotation is smaller. Curl the fingers of the right hand along the direction of rotation. The thumb will point in the direction of the force acting on the conductor.
Electric flux: Electric lines of force in an electric field considered collectively.
Magnetic flux: Lines of force in a magnetic field considered collectively.
Angle of dip: The angle between the direction of the magnetic field at any point and the horizontal.
Weber: The SI unit of magnetic flux, equal to the magnetic flux that, linking a circuit of one turn, produces an emf of one volt when reduced to zero at a uniform rate in one second. 1 Wb = 1 V s.
Electric flux density (or Electric displacement): The flux per unit area through a small area at right angles to the field, which is taken surrounding at any point in an electric field.
Magnetic flux density: Number of flux lines per unit perpendicular area of a magnetic field.
Reluctance: Magnetic counterpart of electrical resistance; or the hindrance to the establishment of magnetic lines of force.
Ampere circuital law (or Ampere’s law): The product of total path elements around a conductor and magnetic flux density in a complete loop equals μo times the total current enclosed by the loop. Mathematically; Σ (B⋅Δl)r = μoI
Permeability: The property of a material by which it changes the flux density in a magnetic field from the value in air.
Absolute permeability (μ): It is the ratio of the magnetic flux density (B) in a substance to the external magnetic field strength (H) , i.e. μ = B / H
Permeability of free space (or Magnetic constant) μo : It is a constant and has a value 4π x 10(-7) H/m in SI system and is given the symbol μo .
Relative permeability (μr) : Relative permeability of a substance is the ratio of its absolute permeability to the permeability of free space; i.e. μr = μ / μo. Note that relative permeability is a ratio and it has no units.
Solenoid: A long helically wound coil of insulated wire.
Phantom: A thing that appears to the sight or other sense but has no material substance.
Parameter: Any of several numerical quantities that can be used jointly to characterize a circuit or network..
Lorentz force: An aspect of the motor effect; the force on a charge Q , moving at velocity v across a magnetic field B. F = BQ sin θ, θ is the angle between v & B.
Alpha particle: A helium nucleus emitted from the nucleus of a radioactive atom.
CRO (or Cathode ray oscilloscope): A device used to display input signal into waveform.
Filament (or Heater): A fine thread of metal, which is heated by the passage of an electric current.
Cathode: The negative electrode of an electronic system.
Fluorescent screen: A surface coated with a luminescent material that fluoresces when excited by electrons, X-rays, etc. and hence displays visual information.
Cathode rays: Radiations emanating from a cathode, under certain conditions, constituting beams of high-speed electrons.
Cathode ray tube: Tube, which makes use of cathode rays.
Coolidge tube: Highly evacuated X-ray tube with filament as source of electrons.
Electron gun: Assembly of electrodes that produces an electron beam.
Grid: In an electronic tube, an electrode used to control the flow of electrons from the cathode to the plate.
Grid bias: The grid to cathode voltage.
Anode: The positive electrode or plate of an electronic tube.
Sweep:
- One complete traverse of the luminous spot on the screen of the CRO is called a sweep.
- Movement along an arc around a given center point.
Time base generator: A voltage applied to the generator that is predetermined function of time and is used to deflect the electron beam of a CRO tube so that the luminous spot traverses the screen in the desired manner.
Saw tooth voltage: A common type of voltage which makes saw tooth waveform.
Saw tooth waveform: A periodic waveform whose amplitude
varies approximately linearly between two values, the time taken in one direction being
very much longer than the time taken in the other.
Three dimensional: Measurement with three references, linked with space.
Synchronize: Occur at the same successive instants of time; keep time with; (of two sets of movements etc.) go at the same rate, have coincident periods, etc.; proceed exactly together;
Synchronous motor: Motor whose speed is an exact multiple of the frequency of the a.c. current operating it.
Frequency: Number of waves that pass across a certain point in the medium in unit time.
Phase: The state or condition as regards its position and direction of motion of a particle of a wave.
Phase angle: The angle between the voltage and current vectors.
Calibration: Determination of the absolute values of the arbitrary indications of an instrument.
Couple: Two forces of equal magnitude acting in opposite directions, but not along the same line.
Torque: The physical quantity, which produces angular acceleration.
Radial: Lines or parts extending or proceeding from a centre; acting or moving along lines proceeding from a center; Lines going outwards from a central region.
Galvanometer: An instrument used to measure minute electric currents.
Deflecting couple: A couple which tends to rotate the coil when a current is passed through the coil of a galvanometer.
Torsional couple: The twist in the suspension wire under the action of deflecting couple in a galvanometer.
Restoring couple: The tendency to untwist the suspension wire and restore the coil to its original position after the action of torsional couple.
Hooke’s law: Within the limits of perfect elasticity stress is directly proportional to strain.
Stress: The distorting force per unit area set up inside the body.
Strain: The change produced in the dimensions of a body under a system of forces.
Lamp and scale arrangement: In sensitive galvanometers the angle of deflection is observed by means of a small mirror attached to the coil along with a lamp and scale arrangement. A beam of light from the lamp is directed towards the mirror. After reflection from the mirror it produces a spot on a translucent scale placed one meter away.
Pivoted type galvanometer (or Moving coil galvanometer): In this type of galvanometer, the coil is pivoted between two jeweled bearings. The restoring torque is provided by two hair springs which also serve as current leads.
Bearing: A part of machine that supports friction.
Current sensitivity: Current per unit scale division of an electric meter.
Voltage sensitivity: Voltage per unit scale division of an electric instrument.
Stable ( or Deadbeat) galvanometer: A galvanometer in which the coil comes to rest quickly after the current passed through it or the current is stopped from flowing through it.
Damping: The reduction in amplitude of an oscillation (or vibration) with time by some form of resistance.
Sensitive galvanometer: A galvanometer is said to be sensitive, if it produces a large deflection for a small current.
Ammeter: A meter used to measure electric current.
Shunt: If two electrical devices or circuits are connected in parallel, either one is said to be in shunt with the other.
Shunt resistance: The resistance connected in parallel with the device or circuit to be shunted.
Voltmeter: A meter used for measuring potential differences.
Calibration: Determination of the absolute values of the arbitrary indications of an instrument.
Ohmmeter: A device for rapid measurement of resistance. It consists of a galvanometer, and adjustable resistance, and a cell connected in series.
AVO meter: It is an instrument which can measure current in amperes, potential difference in volts and resistance in ohms.
Moving coil galvanometer: See the pivoted type galvanometer.
Digital: Pertaining to data in the form of digits.
Digital multimeter: It is an electronic instrument in which digital values are displayed automatically with decimal point, polarity and the unit for V, A or Ω.
Digital recording: A means of recording whereby the audio-frequency signals are converted to a digital form.
Digital circuit: Any circuit designed to respond to discrete values of input voltage and produce discrete output voltage levels.
Digital audio tape: Magnetic tape used for digital recording of sound and also for storing computer information.
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