CASA Part 66 - B-03a Electrical Fundamentals Quiz

Thermionic Emission and Edison's Light Bulb

• Edison's explanation of thermionic emission involves free electrons escaping from a heated filament.
• Forcibly pulling electrons from a cold filament would require significant energy, leading to inefficient and impractical operation.
• The process of free electrons boiling from a conductor’s surface is termed "thermionic emission."
• Higher temperatures of the conductor increase the number of free electrons available for conduction.

Bulb Design and Electrical Properties

• Edison's light bulb contained a vacuum to prevent oxidation and prolong filament lifespan.
• The voltage between two bodies with different potentials is measured in volts (V).
• In a constant EMF circuit, if resistance is doubled, the current is halved according to Ohm's law.
• The unit of electrical resistance is ohm (Ω).

Resistance and Conductor Characteristics

• Resistance increases with the length of a conductor, following the principle that longer conductors impede current flow more than shorter ones.
• The measure of potential difference (PD) between two bodies is also in volts (V).
• For most materials, resistance increases as temperature rises due to increased lattice vibrations that impede electron flow.
• The reciprocal of resistance is called conductance, measured in siemens.

Conductance and Voltage Relationships

• A material with a conductance of 2 siemens has a resistance of 0.5 ohms.
• The relationship between voltage (V), current (I), and resistance (R) can be described by Ohm's Law: V = I × R.

Static Electricity and Humidity Effects

• The major cause of static electricity is the triboelectric effect, where materials become charged through friction.
• The magnitude of the static charge depends on the types of materials and their surface conditions.
• High humidity levels reduce static charges because moisture allows charge dissipation.
• Static becomes more noticeable in dry environments, where humidity is low.
• Increasing humidity to 60% significantly reduces static build-up by enhancing moisture content in the air.

Insulators, Semiconductors, and Conductors

• Insulators have few free electrons in their valence shell, preventing electrical conduction.
• Rubber and its variants are used as insulators due to their ability to block electron flow while being flexible.
• Semiconductors have a moderate number of free electrons allowing controlled conductivity.
• Silicon is a common semiconductor compound due to its favorable electronic properties.

Electrical Charge Characteristics

• The triboelectric series predicts voltage levels generated when two materials are rubbed together based on their relative electron affinity.
• Materials higher on the series tend to lose electrons and become positively charged, whereas those lower gain electrons and become negatively charged.
• Coulomb's Law of Charges, discovered in the 1780s, describes the force between charged objects based on their charges and distances apart.

Conductivity and Material Comparisons

• A worker at a bench can generate electrostatic voltages significantly higher at low humidity levels as per electrostatic tables.
• Silver is the best conductor of electricity, with copper following close behind.
• The most common conductor used in electrical cables is copper, while gold and silver are reserved for special applications due to their high costs.
• The baseline for comparing resistance of conducting materials is often copper.

Industry and Application Considerations

• Steel, aluminum, and other metals are used as conductors in various industries such as construction and manufacturing.
• Resistivity is commonly referred to as a material's inherent opposition to current flow.
• The common focus on resistance in conductors and components usually concerns performance efficiency in applications.
• The descending order of conductivity among silver, copper, gold, aluminum, brass, and carbon prioritizes silver, followed by copper, demonstrating their effectiveness as conductors.

Test your knowledge on means of static generation and electrostatic voltages at different relative humidities with this quiz based on page 31 of training materials for CASA Part 66. Explore scenarios like walking across different surfaces and handling various objects to understand electrostatic voltages.