FSc ICS Notes Physics XII Short Questions & Definitions Chapter 16 Alternating Current 2nd Year Physics Notes Online Taleem Ilmi Hub
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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.
Polarity: The distinction between the positive and negative parameters in an electrical circuit or device.
Waveform (or Wave shape): Of a periodic quantity. The shape of the graph obtained by plotting the instantaneous values of the quantity against time.
Sinusoidal: Of a periodic quantity. Having a waveform that is the same as that of a sine function.
Instantaneous value of current: The magnitude of varying current at any instant of time.
Instantaneous value of voltage: The magnitude of varying voltage at any instant of time.
Peak value: The maximum value attained by an alternating current.
Peak to peak value: It is the sum of the positive and negative peak values.
Root mean square (rms) value of current (or Effective value of current): The magnitude of an alternating current which, in a given resistance, produces heat at the same average rate as that magnitude of steady direct current.
Lagging: The time or angle by which one periodic quantity is delayed with respect to another.
Phase: The state or condition as regards its position and direction of motion of a particle of a wave.
Lead: The interval of time or the angle by which a particular phase in one wave is in advance of the similar phase in another wave.
Lag: The time or angle by which one periodic quantity is delayed with respect to another.
Electrical network: The interconnection of circuit elements (in any way) is called a network.
Electrical circuit: A combination of electrical components that form a conducting path.
A.C. circuit: An electric circuit having alternate voltage source.
Circuit element: A resistor, capacitor, inductor, transistor, or other device used in making up electric circuits.
Inductor: A device usually a coil, possessing inductance which acts on another to produce an electromotive force or a current. A conductor or device in which an electromotive force or current is induced or used on account of its inductance.
Inductive reactance: Reactance in an a.c. circuit, due to inductance, which produces a lagging current.
Capacitive reactance: Reactance in an a.c. circuit, due to capacitance, which produces a lagging voltage.
Inductance: The property of an electric circuit by which a varying current induces an emf in that circuit or a neighboring circuit.
Reactance: The non-resistive opposition to current in an a.c. circuit.
Induction coil: Device for generating high voltages.
Induction motor: Motor with rotating magnetic field.
Capacitance:
- The ratio of the charge on either plate of a capacitor to potential difference between the plates.
- Capacity of electric condenser, or capacitor, to store electric charges.
Resistance: The opposition to the flow of electricity.
Choke (or Choke coil): Coil with high inductive reactance.
Impedance: The joint opposition of reactance and resistance to the current in an a.c. circuit.
Impedance matching: A technique used to insure maximum transfer of energy from the output of one circuit to the input of another.
R-C series circuit: A circuit containing a resistance R and a capacitor C in series excited by an alternating voltage.
R-L series circuit: A circuit containing a resistance R and inductance L in series excited by an A.C. source.
Power dissipation: The continuous loss of energy from an electrical device, by its conversion into heat.
Power factor:
- The cosine of the phase angle between current and voltage in an A.C. circuit.
- Ratio of true power to apparent power.
R-L-C series circuit: A circuit containing a resistance R, inductance L and a capacitor C in series excited by an alternating voltage source.
Resonance: The condition in an a.c. circuit in which the inductive reactance and capacitive reactance are equal and cancel each other. XL = XC
Resonance frequency: The frequency observed when inductive reactance and capacitive reactance have same values in a resonant circuit.
Parallel resonance circuit (or Rejecter circuit): A circuit in which inductor and capacitor are in parallel, so that a minimum current flows at the resonant frequency.
Series resonance circuit (or Acceptor circuit): A condition in which the impedance of a series circuit containing resistance, inductance, and capacitance is equal to the resistance of the circuit, and the voltage across the circuit is in phase with the current.
L-C parallel circuit: A circuit containing an inductance coil l and a capacitor C in parallel, excited by an alternating source of voltage whose frequency can be varied.
Lagging current: An alternating current that, with respect to the applied emf producing it, has a lag.
Three phase: Having three equal alternating voltages between which there are relative phase difference of 120 degree .
A.C. 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.
Oscillating mass-spring system: A system having a spring acting on a body that slides on a frictionless horizontal surface. And energy oscillates between potential and kinetic energies.
Electrical oscillator:
- An L-C circuit in which energy oscillates between a capacitor and an inductor.
- Electric device which generates electric waves.
Search coil: A small coil, in which induced currents are used to measure magnetic field strengths.
Oscillator frequency: The frequency of an oscillator in an electrical resonance circuit.
Beat note (or Beats): The condition whereby two sound waves form an outburst of sound followed by an interval of comparative silence.
Choke (or Choke coil): Coil with high inductive reactance.
Propel: To derive onward, push as a bicycle.
Propeller: One who that which derives forward, especially, a device with blades for causing an airplane or a ship to progress.
Maxwell’s equations: [Simple Understandable Form] A series of classical equations that govern the behaviour of electromagnetic waves in all practical situations. They connect vector quantities applying to any point in a varying electric or magnetic field. The equations are
E ⋅ A = Q / ∈o (Gauss’ law for electricity)
B ⋅ A = 0
(Gauss’ law for magnetism)
ε = - N (Δφ / Δt) (Faraday’s law of induction)
Σ ( B ⋅Δ L)r = μo
I (Ampere’s law)
Electromagnetic waves (or Electromagnetic radiation): Transverse waves in space having an electric component and a magnetic component, each being perpendicular to each other and both perpendicular to the direction of propagation. These do not require any medium for its motion.
Orthogonal: Pertaining to or involving right angles, at right angles; right-angled; rectangular.
Radio waves (or Radio frequency): The frequency of electromagnetic radiation within the range used in radio, i.e. from 3x10(7) to 3x10(9) Hz.
Microwaves: An electromagnetic wave with a wavelength in the range 1 mm to 100 mm, i.e. with a frequency in the range 300 to 3 GHz.
Infrared rays: Electromagnetic waves longer than ordinary light waves but shorter than radio waves; frequencies from 20 to 20,000 cps or Hz.
Visible light (or Light): The aspect of radiant energy of which an observer is visually aware.
Antenna (or Aerial): That part of a radio or TV system from which energy is transmitted into, or received from space or atmosphere.
Transmitting antenna:
- The piece of wire along which charges are made to accelerate.
- Wires mounted to transmit outgoing radio or TV signals, usually elevated.
Receiving antenna:
- A wire in which electrons move with oscillating electric field as that of the wave intercepting the wire.
- Wires mounted to receive incoming radio or TV signals, usually elevated.
Transmitter: In any communications system, the device, apparatus, or circuits by means of which the signal is transmitted to the receiving parts of the system.
Transmitting station: The station or place which transmits the signals to be received by the receiver.
Radio receiver set (or Radio): The apparatus which use the process of communication across space by the transmission and reception of an electromagnetic wave of radio frequency without the use of connecting wires or other material link.
Modulation:
- Variation of radio frequency waves by means of audio frequency waves.
- Variation of the amplitude, frequency or phase of electromagnetic waves, especially for carrier waves.
Amplitude modulation (A.M.): Variation of a carrier wave by changes in the amplitude of the wave.
Frequency modulation (F.M.): Variation of a carrier wave by changes in the frequency of the wave.
Sinusoidal current: The current that has a waveform that is a sine wave.
Sine wave: Waveform resulting from plotting sine of an angle against the angle. Any motion that can be plotted so as to give a sine wave is a simple harmonic motion.
RMS (effective) value: The magnitude of an alternating current which, in a given resistance, produces heat at the same average rate as that magnitude of steady direct current.
Incandescent: Glowing with heat; white-hot.
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