Electrical Concepts Quiz

Basic Electricity & Electronics - Circuit Variables

• A circuit is a mathematical model approximating an actual electrical system.
• Circuit theory is used, instead of electromagnetic field theory.
• Three assumptions guide the model:
  • Electrical effects happen instantly throughout the system (lumped-parameter).
  • The net charge on every component is zero.
  • There's no magnetic coupling between components.

Course Specifications

• Assessment Methods:

  • Final Exam: 40%
  • Mid-term Exam: 20%
  • Tutorial Quiz: 10%
  • Lecture Quiz: 10%
  • Semester Work: (percentage not specified)

• Essential Books:

  • Fundamental Electrical and Electronic Principles by Christopher R. Robertson (3rd edition, 2008)
  • Basic Engineering Circuit Analysis by J. Irwin and R. Nelms (10th edition, 2011)

• Recommended Books:

  • Electric Circuits by J. W. Nilsson and Susan A. Riedel (8th edition, 2008)

Problem Solving

• Identify given and required information.
• Sketch a circuit diagram or visual model.
• Consider various solution approaches.
• Select a method.
• Calculate a solution.
• Use creativity.
• Test the solution.

Balancing Power

• Electrical source (a and b)
• Wires (c, d, and e) carry current from the source.
• Devices (f, g, and h) utilize electrical power (lamps, TVs, etc.)

The International System of Units (SI)

• Length: meter (m)
• Mass: kilogram (kg)
• Time: second (s)
• Electric current: ampere (A)
• Thermodynamic temperature: kelvin (K)
• Amount of substance: mole (mol)
• Luminous intensity: candela (cd)

Derived Units in SI

• Frequency: hertz (Hz), 1/s
• Force: newton (N), kg ⋅ m/s²
• Energy/work: joule (J), N ⋅ m
• Power: watt (W), J/s
• Electric charge: coulomb (C), A ⋅ s
• Electric potential: volt (V), J/C
• Electric resistance: ohm (Ω), V/A
• Electric conductance: siemens (S), A/V
• Electric capacitance: farad (F), C/V
• Magnetic flux: weber (Wb), V ⋅ s
• Inductance: henry (H), Wb/A

Standardized Prefixes

• Units of 10 (powers): atto (a), femto (f), pico (p), nano (n), micro (µ), milli (m), centi (c), deci (d), deka (da), hecto (h), kilo (k), mega (M), giga (G), tera (T)

Example #1

• Signal travels in cable at 80% speed of light.
• Calculate cable length (inches) representing 1 nanosecond (ns).

Voltage and Current

• Charge is bipolar (positive/negative).
• Electric charge exists in discrete quantities (integral multiples of the electronic charge: 1.6022 × 10⁻¹⁹ C).
• Electrical effects are due to charge separation (voltage) and charge motion (current).

Voltage

• Separating positive and negative charges requires energy (w).
• Voltage (v) is the energy per unit charge.
•  1 volt is equal to 1 joule/coulomb (J/C).
• Mathematically, voltage is defined as v = dw/dq

Signs of the Terminals

• A plus sign in terminal 1 indicates terminal 1 is positive with respect to terminal 2.
• Terminals have a voltage even with no current flow.

Example #2

• (a, b) Terminal 2 is positive with respect to terminal 1.
• (c, d) Terminal 1 is positive with respect to terminal 2.
• Voltage can exist independent of current flow.

Notes

• Plus-minus signs in voltage expressions are conventions, not actual polarities.
• Voltage definitions must include positive and negative signs.

Current

• Current (i) is the rate at which charge (q) moves past a given point.
• Measured in amperes (A). Charge in coulombs (C). Time in seconds (s). 1 A = 1 C/s.
• Current has a numerical value and a direction.
• Mathematically, i = dq/dt.

The Direction of Current Flow

• Current direction depends if positive or negative ions are moving

Direction is Important!

• The direction of the arrow is a fundamental part of the current definition.

DC and AC

• Direct Current (DC): constant current.
• Alternating Current (AC): current direction changes with time (sinusoidal variation).

Example #3

• A 5 A current begins at t=0.
• Derive the charge expression for t>0.
• Calculate accumulated charge at t=10 seconds.

Positive Value

• Voltage drop from terminal 1 to terminal 2.
• Voltage rise from terminal 2 to terminal 1
• Positive charge flowing from terminal 1 to terminal 2

Negative Value

• Voltage rise from terminal 1 to terminal 2.
• Voltage drop from terminal 2 to terminal 1.
• Positive charge flowing from terminal 2 to terminal 1.

Power and Energy

• Power (p) is the time rate of expending or absorbing energy (w).
• Mathematically, p = dw/dt = dq/dt · v = i · v.
• Units: Power in watts (W), energy in joules (J). Time in seconds (s), charge in coulombs (C), voltage in volts (V), current in amperes (A).

Positive Sign Convention

• The algebraic sign in power calculations depends on the direction of current and voltage.
• Positive charges moving through a voltage drop lose energy, and moving through a voltage rise gain energy.

Example #4

• Positive power indicates power delivery to circuit.
• Negative power indicates power extraction.
• Calculate power absorbed by each circuit element.

Solution for Example #4

• Calculating power absorbed by each circuit element.
• Consider the directions of current and voltage when evaluating power.

Balancing Power

• The law of conservation of energy dictates that the sum of powers in a circuit equals zero.
• Energy is the capacity for work and is measured in joules (J).

Example #5

• Calculate the power absorbed by each element in the given circuit.
• Determining voltage and current for each component.

Example #5 answer

• Applying the power formula (P = VI) for each circuit element, with correct current and voltage signs and direction.
• Calculate the power absorbed by each element.

Summary

• Review of voltage, current, ideal circuit elements, passive sign convention, and power.