Basic Fundamentals Flashcards
What is the formula for total charge that crosses a conductor’s cross-section in time dt?
dg = nAev dt
Where n is the number of free electrons per cubic meter, A is the area of cross-section, e is the charge of each electron, and v is the drift velocity.
What is the relationship between current (I) and current density (J)?
I = J·A
This indicates that current is the product of current density and the cross-sectional area.
What is the typical drift velocity of electrons in a conductor?
Typically a fraction of a metre per second
Drift velocity is very slow compared to the speed of the electrical field propagation.
What is the formula for current density (J)?
J = ne v
Where n is the free electron density, e is the charge of an electron, and v is the drift velocity.
What is the magnitude of the current density for a copper conductor given n = 10 and e = 1.6 x 10^-19 C?
1.55 x 10^6 A/m^2
This is calculated based on the given values and the relationship J = n e v.
Fill in the blank: The speed with which charge drifts in a conductor is called the _______.
velocity of charge
What is the velocity of propagation of the electrical field in a conductor?
Approximately 3 x 10^8 m/s
This velocity is independent of current and voltage.
True or False: The electron drift velocity is independent of the current flowing and the area of the conductor.
True
What is the Fermi speed in relation to electron movement?
It is the speed at which electrons move, with only a tiny drift velocity superimposed by the applied electric field.
Calculate the magnitude of current if the free-electron density is 10^10 electrons/m^3, the cross-sectional area is 1 cm², and the drift velocity is 1.5 x 10^-3 m/s.
0.24 A
Current is calculated using the formula i = nAev.
What is the significance of the term ‘current density’?
It is the current per unit area and is denoted by the symbol J.
What is Ohm’s Law?
Ohm’s Law states that the current through a conductor between two points is directly proportional to the voltage across the two points.
True or False: Voltage is measured in Amperes.
False. Voltage is measured in Volts.
Fill in the blank: The unit of electrical resistance is ___.
Ohm
What is the formula for calculating power in an electrical circuit?
Power (P) = Voltage (V) x Current (I)
What does a capacitor do in a circuit?
A capacitor stores and releases electrical energy.
Multiple Choice: Which of the following components can store energy? A) Resistor B) Capacitor C) Inductor
B) Capacitor
What is the purpose of a resistor in a circuit?
A resistor limits the flow of electric current.
True or False: In a series circuit, the total resistance is the sum of individual resistances.
True
Fill in the blank: The total current in a parallel circuit is equal to the ___ of the currents through each path.
sum
What is Kirchhoff’s Voltage Law?
Kirchhoff’s Voltage Law states that the sum of the electrical potential differences (voltage) around any closed network is zero.
Multiple Choice: In which type of circuit does current remain the same through all components? A) Series B) Parallel
A) Series
What is a short circuit?
A short circuit is an unintended path of low resistance that allows current to flow, bypassing the intended load.
True or False: The equivalent resistance in a parallel circuit is always less than the smallest individual resistance.
True
Fill in the blank: The unit of capacitance is ___.
Farad
What are the two main types of current?
Alternating Current (AC) and Direct Current (DC)
Multiple Choice: Which law is used to analyze current flow in circuits? A) Ohm’s Law B) Faraday’s Law C) Newton’s Law
A) Ohm’s Law
What is the function of an inductor in a circuit?
An inductor stores energy in a magnetic field when electric current flows through it.
True or False: The total voltage in a series circuit is equal to the sum of the individual voltages across each component.
True
Fill in the blank: The symbol for a resistor in a circuit diagram is ___.
a zigzag line
What is the effect of increasing resistance in a circuit while keeping voltage constant?
The current will decrease.
Multiple Choice: What is the primary purpose of a fuse in a circuit? A) Increase voltage B) Protect against overload C) Store energy
B) Protect against overload
What is the relationship between voltage, current, and resistance known as?
Ohm’s Law
True or False: Capacitors can block DC current while allowing AC current to pass.
True
Fill in the blank: The total capacitance in a parallel circuit is equal to the ___ of the capacitances.
sum
What is a voltmeter used for?
A voltmeter is used to measure the voltage across two points in a circuit.
Multiple Choice: What type of circuit allows multiple paths for current to flow? A) Series B) Parallel
B) Parallel
What does DC stand for in DC network theorems?
Direct Current
True or False: Ohm’s Law states that V = I * R.
True
What is the principle of superposition in DC circuits?
The principle that the response in a linear circuit with multiple sources can be found by considering each source independently.
Fill in the blank: Thevenin’s theorem simplifies a complex circuit to a single __________ and __________.
voltage source, series resistance
What is the formula for calculating equivalent resistance in series circuits?
R_eq = R1 + R2 + … + Rn
True or False: Norton’s theorem states that any linear circuit can be replaced by an equivalent current source in parallel with a resistance.
True
What is the formula for calculating equivalent resistance in parallel circuits?
1/R_eq = 1/R1 + 1/R2 + … + 1/Rn
Define Thevenin equivalent circuit.
A simplified representation of a circuit that consists of a single voltage source in series with a resistance.
What does KCL stand for?
Kirchhoff’s Current Law
What does KVL stand for?
Kirchhoff’s Voltage Law
True or False: KVL states that the sum of all voltages around a closed loop is equal to zero.
True
What is the significance of a short circuit in a DC network?
A short circuit provides a path of low resistance, which can lead to excessive current flow.
Fill in the blank: In a series circuit, the total current is __________.
the same through all components
What is the main purpose of using mesh analysis in DC circuits?
To find the currents in the circuit by applying KVL in the loops.
What is the main purpose of using nodal analysis in DC circuits?
To find the voltages at the nodes in the circuit using KCL.
What is the formula for power in a DC circuit?
P = V * I
True or False: The total power supplied by sources is equal to the total power consumed by loads in a DC circuit.
True
What is the effect of adding resistors in series?
The total resistance increases.
What is the effect of adding resistors in parallel?
The total resistance decreases.
What is a dependent source in a circuit?
A source whose value depends on another voltage or current in the circuit.
Fill in the blank: Thevenin’s theorem can be used to analyze __________.
linear circuits
What is the primary use of Norton’s theorem?
To simplify complex circuits into a current source and parallel resistance.
What is the relationship between Thevenin and Norton equivalents?
They are duals; Thevenin’s voltage source can be converted to Norton’s current source and vice versa.
What do you call a circuit that has only resistors and DC sources?
Linear circuit
True or False: A voltage divider is used to create a lower voltage from a higher voltage in a DC circuit.
True
What is electrical work?
Electrical work is said to be done when an electric charge flows under a potential difference.
Define electrical power.
Electrical power is the rate of transfer of electrical energy or the rate of electrical work.
What is the capacity to do work in mechanics referred to as?
Energy.
What does the skin effect refer to?
The action of alternating current that causes more of a current to flow near the outside surface than in the center of a conductor.
Define eddy current.
Eddy current, or Foucault current, means the current induced in the interior of conducting masses by variation of the magnetic flux.
What is a unilateral circuit?
A unilateral circuit is an electrical circuit in which the properties or characteristics change with respect to current or voltage.
What is a bilateral circuit?
A bilateral circuit is an electrical circuit which has constant properties or characteristics in both directions.
What is a nonlinear network?
A nonlinear network means the network of electrical elements in which the parameters are not constant.
Fill in the blank: Electrical work is the product of _______ and time.
power
True or False: In mechanics, power is defined as the rate of doing energy.
False
Fill in the blank: In electrical work, the flow of charge ‘Q’ occurs under a potential difference ‘______’.
V
Unit of power and electrical energy
Power —– Watt
Electrical Energy—- Watt-hr
