Fundamentals of Electricity and Electronics - Study Notes

Transistors

• NPN Transistor Bias & Current Flow:
  • Base positive relative to emitter (forward biased) → Base-emitter current flows → Collector-emitter current flows.
  • Base and emitter same polarity → No emitter-base current → No collector-emitter current.
• PNP Transistor Bias & Current Flow:
  • Base and emitter same polarity → No emitter-base current → No collector-emitter current.

Electrical Symbols

• Current Limiter: Represented by two triangles point to each other with a line on both sides of the triangles.
• Zener Diode: Represented by a triangle and a Z-like symbol across a horizontal line.
• General-Purpose Diode: Represented by One triangle pointing to a vertical line.

Inductors

• Strengthening a Coil Inductor:
  • Adding more coils close together increases magnetic field strength.
• Material Permeability:
  • Iron allows magnetic force lines to pass most readily.

Capacitors

• Working Voltage (AC Circuit):
  • Should be at least 50% greater than the highest applied voltage.
• Capacitors in Series (Different Ratings):
  • Total capacitance is less than the lowest rated capacitor.
• DC Circuits:
  • Capacitors smooth out pulsations in current/voltage.
  • Store charge, releasing it when values decrease.
• Capacitance Factors:
  • Plate area (larger = greater capacity).
  • Dielectric thickness/distance between plates (closer = greater capacity).
  • Dielectric material/constant (higher constant = greater capacity).
• Capacitors in Series Calculation:
  • When a 0.02-microfarad, a 0.05-microfarad, and a 0.10-microfarad capacitor are connected in series, the total capacitance is 0.0125 microfarad.
• Capacitors in Parallel Calculation:
  • Total capacitance equals the sum of individual capacitances: $CT = C1 + C2 + C3$.
• .02 + .05 + .10 = .170 µF
• Capacitance Formula:$C = Q/E$
  • C = Capacitance (farads)
  • E = Voltage (volts)
  • Q = Charge (coulombs)

Inductive Reactance

• Factors Increasing Inductive Reactance ($X_L$):
  • Increase in inductance (L).
  • Increase in frequency (f).
  • Formula: $X_L = 2πfL$

Capacitors and Inductors

• Capacitors in Parallel: Total capacitance equals the sum of individual capacitances ($CT = C1 + C2 + C3$).
• Inductors in Series (no inductive coupling): Total inductance equals the sum of individual inductances ($LT = L1 + L2 + L3$).
• Inductors in Parallel (different inductances): Total inductance is less than the lowest rated inductor.

Electrical Energy Transfer

• Induction: Transfer of electrical energy from one circuit to another without electrical connections.
• Changing magnetic field induces voltage in adjacent conductors.

AC Circuitry

• Impedance (Z): Combined resistive forces in AC circuit.
  • Vector sum of resistance and total reactance.
  • Expressed in ohms.
• Inductive Reactance ($X_L$): Opposition to AC flow by EMF with generated back voltage.

AC Voltage

• Inductive Reactance ($X_L$) Opposition to the flow of alternating current.
• Effective Voltage: 0.707 times peak voltage.
  • Also called root mean square (rms) voltage.
• AC Values: Unless specified, current/voltage values are assumed to be effective (rms) values.
• Impedance Calculation (AC-series circuit):
  • With inductor reactance $X<em>L$, capacitor reactance $X</em>C$, and resistor resistance R
• $Z = <br /> vert X<em>L - X</em>C<br /> vert + R$
• Resistance in Parallel DC Circuit: Total current equals the sum of currents through individual branches.

Conversions

• Farads to Microfarads: Multiply farads by $10^6$
• Farads to Picofarads: Multiply farads by $10^{12}$

Electrical Power

• Power Comparison:
  • Calculate power using $P = IV$ (Power = Current x Voltage).

Circuit Measurements

• Voltmeter Connection: Connect in parallel with the unit being measured.
• Voltmeter Across Closed Switch: Reads zero voltage (in perfect condition).

Metric Prefixes

• Milli-: Means one-thousandth (0.001).
• kV to Volts: Multiply kV by 1,000.

Electrical Units

• Electrical Quantity: Coulomb is the basic unit.
• Potential Difference: Measured in volts.

Parallel Circuits

• Voltage Drop: Voltage drop across each resistor is the same as the source voltage.
• Current: Total current is the sum of individual branch currents.
• Total Resistance: Always smaller than the smallest resistor.

Series-Parallel Circuits

• Combined Batteries: Batteries in series add voltages; batteries in parallel maintain the same voltage.

Circuit Analysis

• Voltage Drop: Determined by resistance and amperage.
• Electron Flow: Produces magnetic and thermal energy.

Circuit Calculations

• Total Resistance$RT = \frac{E^2}{P}$
• Operating resistance$R = \frac{E^2}{P}$

Power Calculations

• Power: Amount of energy transformed per unit of time; expressed in watts.
• Transformer Operation:$\frac{V<em>p}{V</em>s} = \frac{I<em>s}{I</em>p}$ (Voltage ratio inversely proportional to current ratio).
• Resistor Power Dissipation: $P = I^2 × R$
• Current Flow Through Resistor: $I = \frac{E}{R}$

Circuit Configurations

• Values in Parallel Connections:$V<em>1 = V</em>2 = V_3$
• Voltage Across Resistors: Same in parallel circuits.

Battery Ratings

• Each cell connected in series equals 2 volts, so a 12-cell lead acid battery would be rated for 24 volts.