Basic Concepts of Electrical Engineering Flashcards

Comprehensive practice flashcards covering basic concepts of electrical engineering including charge, current, voltage, power, energy, efficiency, SI units, and circuit elements.

What are the two fundamental theories upon which all branches of electrical engineering are built?

Electric circuit theory and electromagnetic theory.

What are the three basic components of the simple electric circuit shown in the diagram?

A battery (as a source), a lamp (as a load), and connecting wires (for transmission).

What are the mass and charge of a proton as stated in the lecture notes?

The mass is $1.673 \times 10^{-27}\,\text{kg}$ (1836 times that of an electron) and the charge is $1.602 \times 10^{-19}\,\text{C}$.

What is the mass of an electron in kilograms?

$9.11 \times 10^{-31}\,\text{kg}$.

What international system of units was adopted by the General Conference on Weights and Measures in 1960?

The International System of Units (SI).

According to the SI prefixes table, what are the prefix name and symbol for the multiplier $10^{18}$?

Prefix: exa, Symbol: E.

What prefix name and symbol correspond to the multiplier $10^{-15}$ in the SI prefixes table?

Prefix: femto, Symbol: f.

How is most power in the world generated according to the lecture notes?

By converting hot steam into movement using a turbine to turn a shaft connected to a generator.

What type of electrical energy do batteries, fuel cells, and photovoltaics (PV) produce directly?

Direct Current (DC) electrical energy.

What electromechanical device converts mechanical energy into electrical energy using the principle of electromagnetic induction governed by Faraday's law?

A generator.

What is the SI unit of electric charge and its standard symbol?

Coulomb, denoted by $\text{C}$ (with charge denoted by $Q$).

How many electrons are contained in $1\,\text{C}$ of charge?

$6.24 \times 10^{18}$ electrons.

What does the law of conservation of charge state?

Charge can neither be created nor destroyed, only transferred.

What formula expresses Coulomb's Law for the electrostatic force between two point charges?

$$F = \frac{k q_1 q_2}{r^2} = \frac{q_1 q_2}{4 \pi \varepsilon_0 r^2}$$

In Coulomb's Law calculations, what do negative and positive force values indicate?

A negative result indicates an attractive force, while a positive result indicates a repulsive force.

An initially neutral body has $1.7\,\mu\text{C}$ of negative charge removed, and later $18.7 \times 10^{11}$ electrons are added. What is the body's final charge?

$1.4\,\mu\text{C}$ positive charge.

What is the electrostatic force between two positive charges $Q_1 = 2\,\mu\text{C}$ and $Q_2 = 12\,\mu\text{C}$ separated center to center by $10\,\text{mm}$?

$2160\,\text{N}$ (repulsive).

What is electric current, and what is its mathematical relationship to charge $q$?

Electric current is the time rate of change of charge, expressed mathematically as $i = \frac{dq}{dt}$ or $q = \int_{t_0}^t i\,dt$.

What is the basic SI unit of current, and how is it defined in terms of fundamental SI units?

Ampere ($\text{A}$), where $1\,\text{A} = 1\,\text{C/s}$.

What distinguishes direct current (DC) from alternating current (AC)?

Direct current (DC) flows in only one direction, whereas alternating current (AC) changes direction with respect to time.

Which waveform in the figure represents alternating current (AC) and which represents direct current (DC)?

Graph (a) represents alternating current (AC) and graph (b) represents direct current (DC).

How much charge in coulombs is represented by $4,600$ electrons?

$-7.369 \times 10^{-16}\,\text{C}$.

If a charge of $0.16\,\text{C}$ passes through a surface every $64\,\text{ms}$, what is the resulting current in amperes?

$2.5\,\text{A}$.

If the total charge entering a terminal is given by $q = 5t \sin(4\pi t)\,\text{mC}$, what is the current at $t = 0.5\,\text{s}$?

$31.42\,\text{mA}$.

What is the total charge entering a terminal between $t = 1\,\text{s}$ and $t = 2\,\text{s}$ if the passing current is $i = (3t^2 - t)\,\text{A}$?

$5.5\,\text{C}$.

Based on the given charge plot $q(t)$, what is the current $i$ at $t = 1\,\text{ms}$, $t = 6\,\text{ms}$, and $t = 10\,\text{ms}$?

At $t = 1\,\text{ms}$, $i = 40\,\text{A}$; at $t = 6\,\text{ms}$, $i = 0\,\text{A}$; at $t = 10\,\text{ms}$, $i = -20\,\text{A}$.

How is voltage defined between two points in an electric circuit in terms of energy and charge?

Voltage is the energy needed to move a unit charge between two points, expressed mathematically as $v_{ab} = \frac{dw}{dq}$ or $V = \frac{W}{Q}$.

What is the mathematical polarity relation between $v_{ab}$ and $v_{ba}$?

$$v_{ab} = -v_{ba}$$

How are the two voltage representations shown in the figure equivalent?

Point a being $9\,\text{V}$ above point b in (a) is equivalent to point b being $-9\,\text{V}$ above point a in (b).

If it takes $35\,\text{J}$ of energy to move a charge of $5\,\text{C}$ from one point to another, what is the voltage between the two points?

$7\,\text{V}$.

What is the key difference between conventional current direction and electron flow direction?

Conventional current assumes movement of positive charge from positive to negative terminal, while electron flow represents actual electron movement from negative to positive terminal.

What is electrical power, and what is its basic formula in terms of voltage and current?

Power is the time rate of expending or absorbing energy, expressed as $p = v i$ (measured in watts, $\text{W}$).

According to the passive sign convention, when is power positive versus negative?

Power is positive ($p = +v i$) when current enters through the positive terminal (absorbed), and negative ($p = -v i$) when current enters through the negative terminal (supplied).

What does the law of conservation of energy state regarding the sum of power in any electric circuit at any instant?

The algebraic sum of power in a circuit at any instant of time must be zero ($\sum p = 0$).

How many joules are equal to 1 watt-hour ($1\,\text{Wh}$)?

$3,600\,\text{J}$.

What is the total energy consumed by a $100\,\text{W}$ lamp used for $12\,\text{hours}$ and a $1.5\,\text{kW}$ heater used for $45\,\text{minutes}$?

$2.325\,\text{kWh}$ (or $2325\,\text{Wh}$).

What is the relationship between input power $p_i$, output power $p_{out}$, and lost or stored power in a system?

$$p_i = p_{out} + p_{lost\,or\,stored}$$

What is the formula for the overall efficiency $\eta_{total}$ of a cascaded system?

$$\eta_{total} = \eta_1 \cdot \eta_2 \cdot \eta_3 \cdots \eta_n$$

An energy source forces a constant current of $2\,\text{A}$ for $10\,\text{s}$ through a bulb. If $2.3\,\text{kJ}$ of energy is given off, what is the voltage drop across the bulb?

$115\,\text{V}$.

How much energy in joules does a $100\,\text{W}$ electric bulb consume in two hours?

$720,000\,\text{J}$ (or $720\,\text{kJ}$).

A $2\,\text{hp}$ motor operates at $75\%$ efficiency with an applied voltage of $220\,\text{V}$. What is the input power in watts and the input current in amperes?

Input power is $1989.33\,\text{W}$ and input current is $9.04\,\text{A}$.

In a cascaded hydro power system with stage efficiencies $\eta_1 = 90\%$, $\eta_2 = 85\%$, and $\eta_3 = 95\%$, what is the overall system efficiency?

$72.7\%$ (or $72.675\%$).

What primary factor determines the total efficiency of a cascaded system?

The total efficiency is determined primarily by the lowest efficiency link (the weakest link) in the system.

What is the primary difference between active elements and passive elements in electric circuits?

An active element is capable of generating energy, whereas a passive element is not.

Give three examples of passive circuit elements and three examples of active circuit elements.

Passive elements: resistors, capacitors, inductors. Active elements: generators, batteries, operational amplifiers.

What are the four possible types of dependent (controlled) sources in circuit theory?

1. Voltage-controlled voltage source (VCVS)
2. Current-controlled voltage source (CCVS)
3. Voltage-controlled current source (VCCS)
4. Current-controlled current source (CCCS)

What specific type of dependent source is shown on the right-hand side of this circuit diagram?

A current-controlled voltage source (CCVS).

In the circuit shown, calculate power values $p_1$, $p_2$, $p_3$, and $p_4$, and state which elements supply or absorb power.

$p_1 = -100\,\text{W}$ (supplied), $p_2 = 60\,\text{W}$ (absorbed), $p_3 = 48\,\text{W}$ (absorbed), and $p_4 = -8\,\text{W}$ (supplied).

In a cathode-ray tube carrying $10^{15}$ electrons per second, what accelerating voltage $V_o$ is required to achieve a beam power of $4\,\text{W}$?

$25,000\,\text{V}$ (or $25\,\text{kV}$).

For a residential electricity rate with a base charge of $12.00, first 100 kWh at $0.16/kWh, next 200 kWh at $0.10/kWh, and remaining 100 kWh at $0.06/kWh, what are the total bill and average cost per kWh?

Total charge is $54.00 and average cost is 13.5 cents/kWh.