Definitions Flashcards
ohm
the resistance of a circuit in which a current of 1 amp produces a potential difference of 1 volt
capacitance
the property of two conductors that are electrically insulated from each other, whereby electrical energy is stored when a potential difference exists across them
inductance
the property of a coil that results in an e.m.f. being induced in the coil as a result of a change in the current in the coil
conductance
the ability of a circuit to allow the flow of electricity
resistance
a circuit’s opposition to current flow
electromotive force
the stimulus that causes an electric current to flow around a circuit
potential difference
the energy associated with the passage of a unit of charge from one point to the other
Kirchhoff’s current law
at any instant, the algebraic sum of all the currents flowing into any junction in a circuit is zero
Kirchhoff’s voltage law
at any instant, the algebraic sum of all the voltages around any loop in a circuit is zero
junction
any point in a circuit where electrical paths meet
loop
any continuous path around the circuit
period
the length of time between corresponding points in successive cycles of a waveform
frequency
the numbers of cycles a waveform makes within 1 second
peak value
the maximum amplitude of a waveform
peak-to-peak value
the difference between the maximum positive and maximum negative values of a waveform
equal to twice the peak value
charge of an electron
1.6 x 10⁻¹⁹ coulombs
ideal voltage source
a theoretical circuit element that has zero resistance and maintains a constant voltage between its terminals
ideal current source
a theoretical circuit element that has infinite output resistance and always passes a particular current
controlled or dependent voltage source
a voltage that varies in response to some other physical quantity
controlled or dependent current source
a current determined by some physical quantity within a circuit
resistivity of a device
𝑅 = 𝜌𝑙/𝐴
temperature coefficient of resistance
the extent that a material’s resistance changes with temperature
Thevenin’s theorem
As far as its appearance from outside is concerned, any two terminal networks of resistors and energy sources can be replaced by a series combination of an ideal voltage source 𝑉 and a resistor 𝑅, where 𝑉 is the open-circuit voltage of the network and 𝑅 is the resistance that would be measured between the output terminals if the energy sources were removed and replaced by their internal resistance.
Norton’s theorem
As far as its appearance from outside is concerned, any two terminal network of resistors and energy sources can be replaced by a parallel combination of an ideal current source 𝐼 and a resistor 𝑅, where 𝐼 is the short-circuit current of the network and 𝑅 is the resistance that would be measured between the output terminals if the energy sources were removed and replaced by their internal resistance.
open-circuit voltage
voltage with nothing connected to the terminals
short-circuit current
the current that results when the output terminals of a circuit are connected together
principle of superposition
In any linear network of resistors, voltage sources and current sources, each voltage and current in the circuit is equal to the algebraic sum of voltages or currents that would be present if each source were to be considered separately. When determining the effects of a single source, the remaining sources are replaced by their internal resistance.
permittivity of free space
𝜀₀ = 8.85 pF/m
permittivity of air
𝜀 ≈ 1
permittivity
the constant of proportionality in the relationship of the area of the conducting plates of the capacitor and the distance between the plates
electric field strength
the force exerted by on a charged particle at a point in space
dielectric strength
the maximum value of electric field strength that a capacitor can withstand before it breaks down
electric flux
the force between positive and negative charges in an electric field, measured in coulombs
electric flux density
the amount of flux passing through a charged area perpendicular to the flux
magnetic flux density
the strength of magnetic flux at a particular location, expressed in flux per unit area of cross-section
reluctance of a magnetic circuit
a measure of how the circuit opposes the flow of magnetic flux, expressed as a ratio of the magnetomotive force to the magnetic flux
Faraday’s law
The magnitude of the e.m.f. induced in a circuit is proportional to the rate of change of the magnetic flux linking the circuit.
Lenz’s law
The direction of the e.m.f. is such that it tends to produce a current that opposes the change of flux responsible for inducing the e.m.f.
self-inductance
the process where the current in a coil changes, inducing an e.m.f. in that coil which tends to oppose the change in the current
inductance
the property whereby an e.m.f. is induced into a wire as a result of a change in magnetic flux
mutual inductance
a property of two conductors that are linked magnetically, so that a changing current in one produces a changing magnetic flux in the other, producing an induced voltage in the second conductor
ideal transformer
a theoretical device that delivers the same power at the output that it absorbed at the input
step-up transformer
a transformer whose secondary has more turns than its primary and provides an output voltage that is higher than the input voltage, but with a smaller output current
step-down transformer
a transformer whose secondary has fewer turns than its primary, so that it provides a smaller output voltage than its input voltage, but with a greater current
dot notation
notation that indicates the polarity of transformer coil windings
current flowing into each winding at the connection indicated by the dot will produce m.m.f.s in the same direction within the core, and reversing the connections to the coil will invert the corresponding voltage waveform
phase relationship in a resistor
voltage across a resistor is in phase with the current
phase relationship in an inductor
voltage across an inductor leads the current by 90°
phase relationship in a capacitor
voltage across a capacitor lags the current by 90°
active power
average power 𝑃 that is dissipated by the resistive elements in an ac circuit, measured in watts
apparent power
r.m.s. power measured in an ac circuit, disregarding the effects of phase angle, symbolized by 𝑆 = 𝑉𝐼
power factor
the ratio of active power (in watts) to apparent power (in volt amperes)
reactive power
power that is not dissipated, but instead stored and returned to the circuit by its reactive elements, symbolized by 𝑄
frequency response
the way in which the gain of a circuit changes with frequency
transfer function of a circuit
voltage gain described as a ratio of output voltage divided by input voltage
resonance
a situation where the impedance of an RLC network is simply equal to 𝑅
resonant frequency
the frequency at which an RLC circuit is resonant
quality factor
in a resonant circuit, a measure of the ratio of the energy stored to the energy dissipated during each cycle
