Learning Module A6 Flashcards
What is the relationship between the conductivity of materials and their atomic structure?
The conductivity of a substance depends closely on its valence electrons.
What are the characteristics of the best electrical conductors?
Atoms that have three or fewer valence electrons.
Why can outermost electrons in good conductors easily become free electrons?
They are loosely held in orbit.
Give an example of a good electrical conductor and its valence electrons.
Aluminum has three valence electrons; copper has one valence electron.
What defines insulating materials in terms of valence electrons?
Insulating materials have five or more valence electrons.
What is the ideal number of electrons in the valence orbit for an insulator?
Eight electrons.
Why are valence electrons in insulating materials not easily given up for current flow?
They tend to be held more tightly in orbit.
What type of materials are semiconductors considered to be?
Neither good conductors nor good insulators.
How many valence electrons do semiconductor elements have?
Exactly four valence electrons.
Name two commonly used semiconductor elements.
Silicon and germanium.
Which semiconductor is more popular and why?
Silicon, because of its ability to withstand higher temperatures.
Fill in the blank: The best electrical conductors have _______ valence electrons.
three or fewer valence electrons.
Fill in the blank: The ideal insulator contains _______ electrons in its valence orbit.
eight.
True or False: Semiconductors have a higher conductivity than good conductors.
False.
What is the unique arrangement of atoms in purified semiconductor materials called?
Crystal-lattice structure
This structure is essential for the properties of semiconductors.
What process involves atoms sharing their valence electrons to create a stable arrangement?
Covalent bonding
This leads to a stable eight-electron arrangement.
What is the term for introducing a small amount of impurity into a semiconductor?
Doping
Doping improves the conductivity of semiconductors.
What are the two distinct types of semiconductor material produced by doping?
N-type and P-type
The type depends on the impurity used.
What type of semiconductor is formed when an impurity with five valence electrons is introduced?
N-type semiconductor
This involves pentavalent impurities.
Name three pentavalent elements that can be used to dope semiconductors.
- Arsenic
- Antimony
- Phosphorous
These elements contribute free electrons to the semiconductor.
What happens to four of the five valence electrons of a pentavalent impurity atom?
They form covalent bonds with adjoining semiconductor atoms
This bonding is crucial for semiconductor structure.
True or False: In an N-type semiconductor, one electron from the pentavalent impurity is free to move through the crystal.
True
This free electron contributes to electrical conductivity.
What type of semiconductor material is referred to as N-type?
A semiconductor material with a surplus of electrons, or negative charge carriers, within the covalent structure
N-type semiconductors are created through doping with donor atoms that provide extra electrons.
What effect does doping have on the conductivity of N-type semiconductors?
It greatly improves the conductivity due to the free electrons developed by the doping process
The presence of free electrons allows for easier flow of current.
What is the main characteristic of P-type semiconductor material?
It is created by doping with an impurity that has three valence electrons
Trivalent atoms such as aluminum, boron, or gallium are commonly used.
What happens to the valence electrons of the impurity atom in P-type semiconductors?
They form bonds with three adjoining semiconductor atoms, leaving one bond without an electron, creating a ‘hole’
This hole represents the absence of an electron, which behaves as a positive charge carrier.
What is the significance of holes in P-type semiconductors?
Holes act as positive charge carriers and improve the conductivity of the semiconductor material
External electrons are easily attracted into these holes, facilitating current flow.
Fill in the blank: N-type semiconductors are characterized by a surplus of _______.
electrons
True or False: In P-type semiconductors, the absence of an electron is considered negative.
False
List three common trivalent atoms used for doping to create P-type semiconductors.
- Aluminum
- Boron
- Gallium
What is the role of the external electrons in P-type semiconductors?
They are attracted into the holes created by the absence of electrons
This enhances the flow of current through the material.
What happens when an external voltage source is connected across a P-type semiconductor?
Electrons from the current supply move into the holes in the doped semiconductor, jumping from hole to hole throughout the crystal.
What is the term used to describe the flow of positive charges in a semiconductor?
Hole flow or conventional current flow
What effect does doping have on a semiconductor?
Increases the conductivity of the semiconductor
What is commonly used to improve heat dissipation in semiconductor devices?
Aluminum heat sinks
What is a negative temperature coefficient of resistance?
As temperature increases, resistance decreases, leading to increased conductivity
True or False: Semiconductors can be easily destroyed by heat.
True
What must be monitored to prevent damage to semiconductor devices?
Voltage, current, and temperature limits
Fill in the blank: The process of electrons moving in a semiconductor is often referred to as _______.
[electron flow]
What type of devices commonly require heat sinks due to internal power loss?
Diodes and transistors
What happens to the conductivity of semiconductors as current flow produces heat?
It can damage the device due to increased temperature
What is the primary purpose of a heat sink in semiconductor applications?
To dissipate heat generated by the device
What is the maximum allowable bend radius for horizontal cable?
4 times the diameter (D)
This is to prevent damage to the cable.
What is the maximum number of cables allowed in a group to limit crosstalk?
15-20
This helps maintain signal integrity.
What is the fill percentage for a cable tray?
50%
This is to ensure proper airflow and heat dissipation.
What is the maximum length for a conduit containing data cables?
30m or 100 ft
This refers to the maximum distance for cable runs.
What is the internal bend radius for a conduit?
6 times the diameter (D)
This is to ensure the integrity of the cables inside.
What is the maximum pulling tension for Cat 5 cables?
25 pounds
Exceeding this can damage the cable.
What is the spare wire length at the outlet?
450 cm
This is to allow for future modifications or repairs.
What is the maximum number of degrees for bends in conduit containing data cabling?
Two 90 degree bends
Excessive bends can cause signal loss.
What is the maximum distance for flexible metal conduits?
6m or 20 feet
This applies to flexible metal conduit installations.
What is the required headroom for a cable tray?
300mm
This is to ensure easy access and maintenance.
What should be the twist of cables to the termination point?
Half an inch
This helps maintain signal integrity.
What is the maximum cable bend radius for multi-cable?
10 times the diameter (D)
This prevents damage to the cables.
In which division are telecommunications/data categorized?
26/27
This relates to the classification of cable types.
