4A2 Conductors and Insulators Flashcards
Identify properties and material examples for both conductors and insulators.
Define:
Electrical conductivity
The measure of a material’s ability to allow the flow of electric current.
## Footnote
High conductivity materials, like copper, are excellent electrical conductors.
What is the unit of electrical conductivity?
Siemens per meter (S/m)
It is the reciprocal of resistivity.
Fill in the blank:
Materials with high resistance to the flow of electric current are called _______.
insulators
Examples of these include rubber, glass, and plastic.
True or false:
Insulators have infinite resistance.
False
Insulators have very high resistance, but not infinite. Some current can still leak through insulators under high voltages.
Fill in the blank:
Materials with extremely low resistivity are called ________.
superconductors
Superconductors are used in MRI machines and particle accelerators.
Define:
Valence band
The outmost electron orbitals that electrons exist at.
Electrons can jump to the conduction band when given energy, allowing electrical conduction.
How does the valence band structure explain the conductive property of conductors?
The valence band overlaps with the conduction band, allowing electrons to move freely and conduct electricity.
This overlap enables minimal energy input for electron movement.
Why are insulators poor conductors in terms of the valence band?
The valence band is separated from the conduction band by a large energy gap, preventing electrons from moving freely.
This energy gap requires a significant energy input for conduction to occur.
What key property makes superconductors different from ordinary conductors?
- Exhibit zero electrical resistance.
- Expel magnetic fields at a critical temperature.
This phenomenon is known as the Meissner effect.
True or false:
Superconductors have zero electrical resistance at extremely high temperatures.
False
Superconductors exhibit zero resistance at extremely low temperatures. These temperatures often approach absolute zero.
What happens when a conductor becomes a superconductor?
It loses all electrical resistance and expels magnetic fields.
This occurs below a critical temperature specific to each material.
What are two common applications of superconductors?
- MRI machines
- Maglev trains
Their zero-resistance property makes them ideal for generating strong magnetic fields.
Explain the relationship between electrical conductivity and thermal conductivity.
Materials with high electrical conductivity, like metals, also tend to have high thermal conductivity due to the free movement of electrons.
This is described by the Wiedemann-Franz law.
How does an increase in temperature affect resistance in most conductors?
Resistance increases.
This is because increased temperature causes more collisions between electrons and the atomic lattice.
Define:
Electrical resistance
The opposition to electric current flow in a material.
## Footnote
It depends on factors such as material type, length, and cross-sectional area.
Fill in the blank:
The unit for measuring electrical resistance is the ______.
Ohm (Ω)
One ohm is defined as one volt per ampere.
Fill in the blank:
The formula to calculate resistance is _____.
R= V/I
Resistance is voltage divided by current.
What happens to current flow in a circuit when resistance increases?
The current decreases.
This follows Ohm’s law: I=V/R
How does Ohm’s Law relate to the behavior of conductors?
The current through a conductor is directly proportional to the voltage applied across it and inversely proportional to its resistance.
This linear relationship holds true for materials that exhibit consistent resistance, known as ohmic conductors.
True or False:
Ohm’s Law is valid for all conductors.
False
Some materials, such as semiconductors and superconductors, do not follow Ohm’s Law due to their non-linear current-voltage relationship or zero resistance.
What factors affect the resistance of a material?
- Material type
- Length
- Cross-sectional area
- Temperature.
High temperatures typically increase resistance.
Fill in the blank:
Resistance is inversely proportional to _______.
Cross-sectional area
The formula is 𝑅=𝜌𝐿/𝐴, showcasing the inverse relationship. Wider conductors allow more current to flow, reducing resistance.
Define:
Resistivity
Measure of how strongly a material opposes the flow of electric current, typically measured in ohm-meters (Ω·m).
Resistivity is inversely related to conductivity.
What is the relationship between resistance and resistivity?
Resistance is calculated as R=ρ L/A
Where ρ is resistivity, L is length, and A is cross-sectional area. Longer and thinner wires have higher resistance.
Define:
Semiconductor
A material that can act as both insulators and conductors under different conditions.
Silicon is a common component in semiconductors found in everyday devices.
List factors that can make a semiconductor act as an insulator or conductor.
- Light
- Temperature
- External energy sources
- Electric field
The behavior of semiconductors depends on energy input and structural modifications.
Why are semiconductors essential in modern electronics?
They have controllable conductivity and are used in diodes, and integrated circuits.
Their conductivity can be modified by doping or applying voltage. A modern example is silicon.
Explain the role of doping in semiconductors.
It involves adding impurities to a semiconductor to enhance its conductivity.
Common dopants are phosphorus and boron.
Name two practical uses of semiconductors.
- Microchips
- Solar cells
Silicon is the most commonly used semiconductor material.
Explain how a semiconductor can change from an insulator to a conductor when exposed to light.
A semiconductor, like pure selenium, is normally an insulator. When exposed to the right light color, it becomes conductive, allowing accumulated charges to dissipate.
This phenomenon is the basis of photoelectric applications.
True or false:
A charged selenium plate loses its surface charge immediately when kept in darkness.
False
In darkness, a selenium plate retains its charge for a long time.
Define:
Transistors
A semiconductor device used to amplify or switch electronic signals and power.
Transistors are the building blocks of modern electronic devices.
True or false:
Transistors are made primarily from insulating materials.
False
Transistors are made from semiconductors.
What is the role of transistors in electronics?
Transistors act as switches or amplifiers for electrical signals.
Transistors are made from semiconductor materials like silicon.
Explain why metals are good conductors.
Metals have a high density of free electrons that can move easily under an electric field.
This free electron model is key to their high conductivity.
What key material properties make something suitable for electrical wiring?
- High electrical conductivity
- Malleability
Copper and aluminium are widely used because of these properties.
Which metal is commonly used in electrical wiring due to its conductivity?
Copper
Copper has thousands of free electrons that allow electric charge to flow efficiently.
True or false:
Gold is used in electronics primarily because it has the best conductivity.
False
Gold is used because it resists corrosion, not because it has the best conductivity.
Why is copper preferred over aluminum for household wiring?
Copper conducts better and is stronger and less reactive than aluminum.
Aluminum is lighter and cheaper, but oxidizes easily, increasing fire risk.
Why is aluminum used in power transmission lines?
It has good conductivity and is lightweight.
Despite being less conductive than copper, aluminum is cheaper and lighter.
Explain why silver is the best electrical conductor.
Silver has the highest density of free electrons, making it the best conductor.
Copper is more commonly used due to its lower cost and good conductivity.
Why are alloys like nichrome used in heating elements?
They have high resistivity and can withstand high temperatures.
The resistance of nichrome generates heat when current flows through it.
Fill in the blank:
_______ is widely used as an electrical insulator in high-voltage systems.
Ceramic
These resist heat and electricity, making them ideal for insulating power lines and equipment.
Explain why rubber is a good electrical insulator.
Rubber has tightly bound electrons that do not move freely, preventing current flow.
Insulators block or resist the flow of electricity.
True or false:
Glass is a better insulator than wood.
True
Glass has higher resistance to electrical flow than wood, especially when dry.
Fill in the blank:
_____ is a superconductor at cryogenic temperatures.
Lead
Lead becomes a superconductor below 7.2 K (-266°C).
Name a non-metallic material with high electrical conductivity.
Graphene
It is an allotrope of carbon with remarkable conductivity properties.
True or false:
Plastics are conductive materials.
False
Plastics are insulators and block current flow.
Explain why diamond, a form of carbon, is an excellent electrical insulator.
A diamond has a strong covalent bond structure that tightly holds electrons.
Its crystal lattice prevents electron movement.
Why is graphite a conductor while diamond is an insulator, despite both being forms of carbon?
Graphite has free-moving electrons in its layered structure, unlike diamond.
The bonding structure makes the difference.
Name a common household application of insulators.
Plastic coatings on electrical wires.
They prevent electrical shocks.
True or false:
Water is a good electrical conductor.
False
Pure water is an insulator, but impurities, ions, can make it conductive.
What types of materials are typically used for circuit board substrates?
- Fiberglass
- Epoxy resin
These materials are insulating and heat-resistant.
Fill in the blank:
______ is often used for high-frequency signal transmission due to its low resistance.
Silver
Despite its cost, silver’s conductivity makes it ideal for certain applications.
Fill in the blank:
_______-film resistors are often used to limit current in electronic circuits.
Carbon
These resistors are inexpensive and reliable for many applications.
What role do semiconductors play in medical devices?
They power devices like pacemakers, glucose monitors, and imaging equipment.
They enable precision control and efficient energy use.
Name a natural material with conductive properties.
Pyrite
(fool’s gold)
Pyrite’s conductive properties have potential applications in renewable energy technologies.
How do semiconductors contribute to artificial intelligence (AI) technologies?
They power advanced AI chips for machine learning tasks in devices like smartphones and servers.
Efficient processing enables faster and smarter AI computations.
What is a practical use of conductive polymers?
They are used in flexible electronics like wearable health monitors.
Conductive polymers combine electrical properties with material flexibility.
Why is copper commonly used in lightning rods?
Copper is an excellent conductor, efficiently directing lightning strikes safely into the ground.
Its high conductivity and corrosion resistance make it ideal for lightning protection systems.
