Test Compilation PHY 102 11

Physics and Electronics Study Summary

This document covers a range of topics in Physics and Electronics, primarily focusing on electromagnetism, circuit theory, and semiconductor physics.

I. Electrostatics

• Electric Field Intensity (E):
  • Definition: Force per unit charge (E = F/q).
  • Unit: Newtons per Coulomb (N/C) or Volts per meter (V/m).
  • Between parallel plates: E = V/d.
  • From a point charge: E = kQ/r².
• Electric Potential Difference (V):
  • Definition: Work done per unit charge (V = W/q).
  • Unit: Volts (V).
  • Change in potential energy: ΔU = qΔV.
  • Equipotential surfaces: Electric field lines are perpendicular to equipotential surfaces. The electric field *along* an equipotential surface is zero.
• Capacitance (C):
  • Definition: Ability to store electric charge (C = Q/V).
  • Unit: Farads (F).
  • Parallel plate capacitor: C = ε₀A/d.
  • Effect of dielectric/metal sheet: Inserting a metal sheet of thickness t between plates of separation d changes capacitance to C = ε₀A / (d-t). If t = d/2, capacitance doubles.
  • Energy stored: E = 0.5CV².
  • Equivalent Capacitance:
    • Series: 1/C_eq = 1/C₁ + 1/C₂ + ...
    • Parallel: C_eq = C₁ + C₂ + ...
  • Capacitor charging: Maximum charging current I_max = V/R, maximum charge stored Q_max = CV.
• Electric Dipole:
  • Characteristic: Has no net charge but produces a net electric field.

II. Current Electricity and Circuits

• Ohm's Law:
  • Principle: V = IR.
  • Applicability: Can be used only for linear circuits or components.
  • Effect of potential difference: If potential difference across a resistor is doubled, the current through it is doubled (assuming constant resistance).
• Resistance (R):
  • Unit: Ohms (Ω).
  • Temperature dependence: R_t = R_0 * (1 + αΔT), where α is the temperature coefficient of resistance.
  • Equivalent Resistance:
    • Series: R_eq = R₁ + R₂ + ...
    • Parallel: 1/R_eq = 1/R₁ + 1/R₂ + ...
• Conductivity (σ):
  • Definition: Reciprocal of resistivity (ρ). σ = 1/ρ.
  • Relation to Resistance: R = ρL/A, so σ = L/(RA).
  • Unit: Siemens per meter (S/m) or Ohm⁻¹meter⁻¹ (Ω⁻¹m⁻¹).
• Kirchhoff's Current Law (KCL):
  • Principle: The algebraic sum of currents entering a node (junction) is zero, or the sum of currents entering equals the sum of currents leaving.
  • Application: Applied at a Node.
• Current (I) and Charge (Q):
  • Relationship: Q = It (Charge = Current × Time).
  • Unit of Charge: Coulomb (C).
  • Conventional Current Direction: The direction of flow of positive charge.
• Measurement Devices:
  • Voltmeter or Potentiometer: Used for measuring potential difference.
• EMF vs. Terminal Potential Difference:
  • The electromotive force (EMF) of a battery is equal to its terminal potential difference when no current is flowing or if the internal resistance is zero. Otherwise, terminal potential difference is less than EMF when current flows.

III. Magnetism and Electromagnetism

• Magnetic Field (B):
  • Unit: Tesla (T).
  • Force on a current-carrying wire: F = BILsinθ.
  • Force on a moving charge: F = qvBsinθ.
  • Magnetic field lines:
    • Go from North pole to South pole outside the magnet, and South to North inside.
    • Are most concentrated at the poles.
    • Never cross one another.
    • Do *not* pass through non-magnetic materials like copper without interaction (copper is diamagnetic but typically considered non-magnetic in basic contexts).
  • Field without magnetic poles: An electric field does not have magnetic poles.
• Magnetic Flux (Φ):
  • Definition: Measure of the total magnetic field passing through a given area.
  • Formula: Φ = BAcosθ, where θ is the angle between the magnetic field and the normal to the surface.
  • Unit: Webers (Wb).
• Electromagnetic Induction:
  • Phenomenon: The production of an induced EMF with the aid of a magnetic field.
  • Effect of magnet movement: Accelerating a magnet inside a coil induces current, which changes or reverses direction depending on relative motion.
• Induced Magnetism:
  • Example: A bar magnet attracting a piece of soft iron.
• Transformers:
  • Principle: Relates turns ratio to current ratio: N_p/N_s = I_s/I_p. (Assuming ideal transformer).

IV. AC Circuits and Inductors

• RMS Current (I_rms):
  • Definition: Root Mean Square current, I_rms = I_peak / √2.
  • Calculation: For a resistor, I_rms = V_rms / R.
• Inductors:
  • Inductive Reactance (X_L): X_L = 2πfL (or ωL).
  • Current in inductor (AC): I = V/X_L.
  • RL circuit time constant (τ): τ = L/R. Doubling resistance decreases the time constant to one-half.
• RLC Series Circuits:
  • Impedance (Z): Z = √(R² + (X_L - X_C)²).
  • RMS Current: I_rms = V_rms / Z.
• AC Voltage Equation:
  • V = V₀ sin(ωt), where ω = 2πf (angular frequency). Frequency f = ω/(2π).

V. Semiconductor Physics

• Intrinsic Semiconductors:
  • Properties: Each semiconductor atom undergoes paired sharing of electrons with four neighboring atoms. Conduction is due equally to holes and electrons. At room temperature, the number of electrons and holes are Equal.
  • Mechanism: Current flows due to the breakage of crystal bonds.
  • Band structure: Lies between that of metals and insulators.
• Extrinsic Semiconductors (Doping):
  • P-type semiconductor: Created by doping with Group III elements (e.g., Silicon with Boron), leading to excess holes in the valence band.
  • N-type semiconductor: Created by doping with Group V elements, leading to excess electrons in the conduction band.
• Insulators and Semiconductors:
  • Energy bands: Insulators have wide forbidden bands; semiconductors have narrow forbidden bands.
• PN Junction Diode:
  • Forward Bias: Requires +ve terminal to P-type and -ve terminal to N-type. Current rises exponentially, not linearly.
  • Reverse Bias: Reverse bias current is usually very small but not absolutely zero.
  • Depletion Region: The width of the depletion region decreases in forward bias and increases in reverse bias. It is *not* unchanged when forward biased.
• Temperature effect on Semiconductors:
  • When a pure semiconductor is heated, its resistance decreases (due to a negative temperature coefficient of resistance).

VI. General Physics & Units

• Work, Power, Efficiency:
  • Efficiency of a motor: η = (Output Work / Input Energy) × 100%.
  • Input Energy = Power × Time.
• Units:
  • Derived unit Tesla (for magnetic field strength) is related to Amperes (A), kilograms (kg), and seconds (s).
  • Correct units for electric field strength: N/C or V/m.
  • Power unit examples: Watt (W), kilowatt-hour (kW·h).
  • Coulomb's law constant (k): Dimensionally equivalent to N·m²/C².