Module 2: Physics

Module 2: Physics – EASA Part-66 B2 Study Material

1. Module Overview

Module 2 of the EASA Part-66 Basic Knowledge Syllabus (Appendix I) provides the foundational physical principles required for the safe and effective maintenance of modern aircraft systems. For the B2 (Avionics) category, a deeper understanding of electrical, electronic, and wave-related phenomena is critical. This module bridges the gap between pure theory and practical aeronautical applications, covering everything from the basic SI units used in measurements to the complex behaviours of gyroscopes and thermodynamic systems.

The syllabus is structured into several key sub-modules:

• 2.1 Matter and SI Units
• 2.2 Mechanics (Statics, Kinetics, Dynamics)
• 2.3 Thermodynamics
• 2.4 Optics and Light
• 2.5 Wave Motion and Sound
• 2.6 Electricity (DC and AC)
• 2.7 Magnetism
• 2.8 Electronics (Basic)
• 2.9 Gyroscopic Principles
• 2.10 Fluid Mechanics (Hydraulics and Pneumatics)

This study material synthesises the core knowledge from these areas, focusing on the application of fundamental laws and the performance of standard calculations that you will encounter in your daily duties as a certifying technician.

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2. Key Concepts Explained in Detail

2.1 The International System of Units (SI) and Matter

All physical measurements in aviation are based on the International System of Units (SI). As a certifying technician, you must be fluent in these units and their conversions.

• Base Units: The seven base units form the foundation. The most relevant for B2 are:
• Metre (m): Unit of length.
• Kilogram (kg): Unit of mass.
• Second (s): Unit of time.
• Ampere (A): Unit of electric current.
• Kelvin (K): Unit of thermodynamic temperature.
• Derived Units: These are formed by combining base units. Critical examples include:
• Force: Newton (N) = kg·m/s².
• Pressure: Pascal (Pa) = N/m².
• Energy/Work: Joule (J) = N·m.
• Power: Watt (W) = J/s.
• Frequency: Hertz (Hz) = s⁻¹.
• Electric Charge: Coulomb (C) = A·s.
• Electric Potential: Volt (V) = W/A.
• Electric Resistance: Ohm (Ω) = V/A.
• Capacitance: Farad (F) = C/V.
• Magnetic Flux: Weber (Wb) = V·s.
• Magnetic Flux Density: Tesla (T) = Wb/m².

Key Conversions for Avionics Technicians:

• Pressure: 1 hPa (hectopascal) = 100 Pa. Standard atmospheric pressure at sea level is 1013.25 hPa, which equals 101,325 Pa.
• Temperature:
• Celsius to Fahrenheit: °F = (°C × 9/5) + 32
• Fahrenheit to Celsius: °C = (°F − 32) × 5/9
• Celsius to Kelvin: K = °C + 273.15

2.2 Mechanics: Statics and Dynamics

This section deals with forces, moments, and the motion of objects. It is fundamental to understanding aircraft structural loads and control system forces.

Statics (Forces in Equilibrium)

• Force: A vector quantity that causes a change in an object's motion. Its SI unit is the Newton (N).
• Moment (Torque): The turning effect of a force. It is calculated as the product of the force and the perpendicular distance from the pivot point to the line of action of the force.
• Formula: Torque (τ) = Force (F) × Distance (d)
• SI Unit: Newton-metre (N·m).
• Example: If a torque of 20 N·m is required on a bolt and the torque wrench is 0.25 m long, the force applied at the handle is F = τ / d = 20 N·m / 0.25 m = 80 N.
• Equilibrium: An object is in a state of equilibrium when the resultant force and the resultant moment acting upon it are both zero. This means there is no acceleration.

Dynamics (Forces in Motion)

• Newton's First Law (Law of Inertia): An object at rest stays at rest, and an object in motion stays in motion at a constant velocity, unless acted upon by an external resultant force.
• Application: If an aircraft is climbing at a constant velocity, the thrust, drag, lift, and weight are all balanced. The resultant force is zero, and therefore, acceleration is zero.
• Newton's Second Law: The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
• Formula: Force (F) = Mass (m) × Acceleration (a)
• Newton's Third Law: For every action, there is an equal and opposite reaction. This is the principle behind jet propulsion.

2.3 Thermodynamics

Thermodynamics concerns the relationships between heat, work, and energy. For B2, the key focus is on the behaviour of gases, which is essential for understanding pneumatic systems and engine cycles.

• The Ideal Gas Laws: These laws describe the relationship between Pressure (P), Volume (V), and Temperature (T) for an ideal gas.
• Boyle's Law (Constant Temperature): The pressure of a gas is inversely proportional to its volume.
• Formula: P₁V₁ = P₂V₂
• Application: If you compress a gas (decrease volume), its pressure increases proportionally, provided the temperature remains constant.
• Charles's Law (Constant Pressure): The volume of a gas is directly proportional to its absolute temperature (in Kelvin).
• Formula: V₁/T₁ = V₂/T₂
• Gay-Lussac's Law (Constant Volume): The pressure of a gas is directly proportional to its absolute temperature.
• Formula: P₁/T₁ = P₂/T₂
• The General Gas Law: This combines all three laws into a single equation.
• Formula: (P₁V₁)/T₁ = (P₂V₂)/T₂

2.4 Wave Motion and Sound

Understanding wave properties is crucial for B2 technicians working with communication, navigation, and radar systems.

• Wave Properties:
• Frequency (f): The number of complete wave cycles per second. Unit: Hertz (Hz).
• Wavelength (λ): The distance between two consecutive corresponding points on a wave (e.g., crest to crest). Unit: metre (m).
• Velocity (v): The speed at which the wave propagates through a medium.
• The Wave Equation:
• Formula: Velocity (v) = Frequency (f) × Wavelength (λ)
• Electromagnetic Waves (Radio, Light): These travel at the speed of light in a vacuum, which is approximately c = 3 × 10⁸ m/s.
• Example: A radio signal at 300 MHz has a wavelength of λ = c / f = (3 × 10⁸ m/s) / (300 × 10⁶ Hz) = 1 metre.
• Sound Waves: These are mechanical waves that require a medium (air, water, solid) to travel. The speed of sound in air at sea level is approximately 340 m/s.
• Example: A 2 kHz sound wave has a wavelength of λ = v / f = 340 m/s / 2000 Hz = 0.17 metres.

2.5 Fluid Mechanics (Hydraulics)

Hydraulic systems are used extensively in aircraft for actuating flight controls, landing gear, and brakes. The fundamental principle governing these systems is Pascal's Law.

• Pascal's Law: Pressure applied to a confined fluid is transmitted equally in all directions throughout the fluid, undiminished.
• Pressure Calculation:
• Formula: Pressure (P) = Force (F) / Area (A)
• SI Unit: Pascal (Pa), where 1 Pa = 1 N/m².
• Example: A force of 500 N applied to a piston with an area of 0.02 m² generates a pressure of P = 500 N / 0.02 m² = 25,000 Pa (25 kPa).
• Hydraulic Multiplication: This principle allows a small force applied to a small-area piston to create a large force on a larger-area piston. The pressure is the same throughout the system, so F₁/A₁ = F₂/A₂.

2.6 Electricity and Magnetism

This is the core of the B2 syllabus. A thorough understanding of DC and AC circuits, capacitance, and magnetism is non-negotiable.

DC Circuits

• Ohm's Law: The relationship between voltage (V), current (I), and resistance (R).
• Formula: Voltage (V) = Current (I) × Resistance (R)
• Example: A 12 V drop across a resistor with 3 A of current flow means the resistance is R = V / I = 12 V / 3 A = 4 Ω.
• Electrical Power (Joule's Law): The rate at which electrical energy is converted into another form of energy (e.g., heat).
• Formulas:
• Power (P) = Voltage (V) × Current (I)
• Power (P) = Current² (I²) × Resistance (R)
• Power (P) = Voltage² (V²) / Resistance (R)
• Examples:
• A current of 2 A through a resistor with a 12 V drop dissipates P = V × I = 12 V × 2 A = 24 W.
• A current of 2 A through a 50 Ω resistor dissipates P = I² × R = (2 A)² × 50 Ω = 200 W.

Capacitance

• Capacitor: A passive component that stores electrical energy in an electric field.
• Capacitance (C): The ability of a capacitor to store charge per unit voltage.
• Formula: Capacitance (C) = Charge (Q) / Voltage (V)
• SI Unit: Farad (F), where 1 F = 1 C/V.
• Example: A capacitor storing 0.02 C at 50 V has a capacitance of C = 0.02 C / 50 V = 0.0004 F = 400 µF.

Magnetism

• Magnetic Flux (Φ): The total quantity of magnetism, considering the strength and extent of a magnetic field. Unit: Weber (Wb).
• Magnetic Flux Density (B): The amount of magnetic flux passing through a unit area perpendicular to the field.
• Formula: B = Φ / A
• SI Unit: Tesla (T), where 1 T = 1 Wb/m².
• Application: This is a critical parameter in the design of transformers, electric motors, and generators.

2.7 Gyroscopic Principles

Gyroscopes are fundamental to inertial navigation systems, attitude indicators, and autopilot systems.

• Gyroscope: A spinning wheel or rotor mounted so that its axis can freely rotate in any direction.
• Key Properties:

1. Rigidity in Space: A spinning gyroscope tends to maintain its axis of rotation fixed in space, resisting any external force that tries to change its orientation. This property is used as an attitude reference in inertial navigation systems.
2. Precession: When an external force is applied to the axis of a spinning gyroscope, the resultant movement occurs at a point 90° from the point of application, in the direction of rotation. This is known as precession.

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3. Important Formulas and Relationships

The following table summarises the essential formulas for quick reference.

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4. Common Relationships Between Concepts

• Mechanics and Electricity: The concept of "work" (Joules) in mechanics is directly equivalent to "electrical energy" (also Joules). Power (Watts) is the rate of doing work in both domains. This is why the formula P = V × I yields watts, the same unit as P = F × v (force times velocity).
• Thermodynamics and Pneumatics: The Ideal Gas Laws are the theoretical foundation for pneumatic systems. When a gas is compressed quickly (e.g., in a compressor), its temperature rises (Gay-Lussac's Law). Conversely, when it expands rapidly, it cools. This is why water vapour condenses in expanding air.
• Wave Motion and Electrical Engineering: The same mathematical relationships govern AC circuits and wave propagation. The frequency of an AC signal is the number of cycles per second, and its wavelength in a cable is determined by the wave equation, albeit at a slower velocity than in free space.
• Magnetism and Electricity: They are inseparable. A moving electric charge creates a magnetic field, and a changing magnetic field induces an electric current (electromagnetic induction). This is the principle behind transformers, generators, and motors.

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5. Typical Exam Focus Points

Based on the EASA Part-66 exam format, you should be prepared for:

• Unit Conversions: Be highly proficient in converting between hPa and Pa, °F and °C, and between different metric prefixes (e.g., millimetres to metres, microfarads to farads).
• Direct Formula Application: Most calculation questions are straightforward applications of a single formula. You will be expected to rearrange formulas to solve for the unknown variable (e.g., finding force from torque and distance, or resistance from voltage and current).
• Fundamental Definitions: Questions often test your knowledge of SI units and definitions. For example, knowing that the Tesla is the unit of magnetic flux density, not the Weber (which is magnetic flux).
• Conceptual Understanding of Laws: You must understand the conditions under which laws apply. For example, Boyle's Law only applies at a constant temperature. Similarly, Newton's First Law dictates that constant velocity implies zero resultant force.
• Practical Application: Many questions are framed in a practical maintenance context (e.g., "A technician measures...", "During a ground check..."). This tests your ability to apply theory to real-world scenarios. Always pay attention to the units given in the question to guide your calculation.