4A2 Conductors and Insulators

Question 1

Define:

Electrical conductivity

Answer 1

The measure of a material’s ability to allow the flow of electric current.
## Footnote

High conductivity materials, like copper, are excellent electrical conductors.

Question 2

What is the unit of electrical conductivity?

Answer 2

Siemens per meter (S/m)

It is the reciprocal of resistivity.

Question 3

Fill in the blank:

Materials with high resistance to the flow of electric current are called _______.

Answer 3

insulators

Examples of these include rubber, glass, and plastic.

Question 4

True or false:

Insulators have infinite resistance.

Answer 4

False

Insulators have very high resistance, but not infinite. Some current can still leak through insulators under high voltages.

Question 5

Fill in the blank:

Materials with extremely low resistivity are called ________.

Answer 5

superconductors

Superconductors are used in MRI machines and particle accelerators.

Question 6

Define:

Valence band

Answer 6

The outmost electron orbitals that electrons exist at.

Electrons can jump to the conduction band when given energy, allowing electrical conduction.

Question 7

How does the valence band structure explain the conductive property of conductors?

Answer 7

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.

Question 8

Why are insulators poor conductors in terms of the valence band?

Answer 8

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.

Question 9

What key property makes superconductors different from ordinary conductors?

Answer 9

• Exhibit zero electrical resistance.
• Expel magnetic fields at a critical temperature.

This phenomenon is known as the Meissner effect.

Question 10

True or false:

Superconductors have zero electrical resistance at extremely high temperatures.

Answer 10

False

Superconductors exhibit zero resistance at extremely low temperatures. These temperatures often approach absolute zero.

Question 11

What happens when a conductor becomes a superconductor?

Answer 11

It loses all electrical resistance and expels magnetic fields.

This occurs below a critical temperature specific to each material.

Question 12

What are two common applications of superconductors?

Answer 12

1. MRI machines
2. Maglev trains

Their zero-resistance property makes them ideal for generating strong magnetic fields.

Question 13

Explain the relationship between electrical conductivity and thermal conductivity.

Answer 13

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.

Question 14

How does an increase in temperature affect resistance in most conductors?

Answer 14

Resistance increases.

This is because increased temperature causes more collisions between electrons and the atomic lattice.

Question 15

Define:

Electrical resistance

Answer 15

The opposition to electric current flow in a material.
## Footnote

It depends on factors such as material type, length, and cross-sectional area.

Question 16

Fill in the blank:

The unit for measuring electrical resistance is the ______.

Answer 16

Ohm (Ω)

One ohm is defined as one volt per ampere.

Question 17

Fill in the blank:

The formula to calculate resistance is _____.

Answer 17

R= V/I

Resistance is voltage divided by current.

Question 18

What happens to current flow in a circuit when resistance increases?

Answer 18

The current decreases.

This follows Ohm’s law: I=V/R

Question 19

How does Ohm’s Law relate to the behavior of conductors?

Answer 19

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.

Question 20

True or False:

Ohm’s Law is valid for all conductors.

Answer 20

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.

Question 21

What factors affect the resistance of a material?

Answer 21

• Material type
• Length
• Cross-sectional area
• Temperature.

High temperatures typically increase resistance.

Question 22

Fill in the blank:

Resistance is inversely proportional to _______.

Answer 22

Cross-sectional area

The formula is 𝑅=𝜌𝐿/𝐴, showcasing the inverse relationship. Wider conductors allow more current to flow, reducing resistance.

Question 23

Define:

Resistivity

Answer 23

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.

Question 24

What is the relationship between resistance and resistivity?

Answer 24

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.

Question 25

# Define: Semiconductor

Answer 25

A material that can **act as both insulators and conductors** under different conditions. ## Footnote Silicon is a common component in semiconductors found in everyday devices.

Question 26

List factors that can make a **semiconductor** act as an insulator or conductor.

Answer 26

* Light * Temperature * External energy sources * Electric field ## Footnote The behavior of semiconductors depends on energy input and structural modifications.

Question 27

Why are **semiconductors** essential in **modern electronics**?

Answer 27

They have **controllable conductivity** and are used in diodes, and integrated circuits. ## Footnote Their conductivity can be modified by doping or applying voltage. A modern example is silicon.

Question 28

Explain the role of **doping** in semiconductors.

Answer 28

It involves **adding impurities to a semiconductor** to enhance its conductivity. ## Footnote Common dopants are phosphorus and boron.

Question 29

Name two practical uses of **semiconductors**.

Answer 29

1. Microchips 2. Solar cells ## Footnote Silicon is the most commonly used semiconductor material.

Question 30

Explain how a **semiconductor** can change from an insulator to a conductor when exposed to **light**.

Answer 30

A semiconductor, like pure **selenium**, is normally an insulator. When exposed to the right light color, it becomes conductive, allowing accumulated charges to dissipate. ## Footnote This phenomenon is the basis of photoelectric applications.

Question 31

# True or false: A **charged selenium plate** loses its surface charge immediately when kept in darkness.

Answer 31

False ## Footnote In darkness, a selenium plate retains its charge for a long time.

Question 32

# Define: Transistors

Answer 32

A **semiconductor device** used to amplify or switch electronic signals and power. ## Footnote Transistors are the building blocks of modern electronic devices.

Question 33

# True or false: **Transistors** are made primarily from **insulating materials**.

Answer 33

False ## Footnote Transistors are made from semiconductors.

Question 34

What is the role of **transistors** in **electronics**?

Answer 34

Transistors **act as switches or amplifiers** for electrical signals. ## Footnote Transistors are made from semiconductor materials like silicon.

Question 35

Explain why **metals** are good **conductors**.

Answer 35

Metals have a high density of **free electrons** that can move easily under an electric field. ## Footnote This free electron model is key to their high conductivity.

Question 36

What **key material properties** make something suitable for electrical wiring?

Answer 36

* High electrical conductivity * Malleability ## Footnote Copper and aluminium are widely used because of these properties.

Question 37

Which metal is commonly used in **electrical wiring** due to its **conductivity**?

Answer 37

Copper ## Footnote Copper has thousands of free electrons that allow electric charge to flow efficiently.

Question 38

# True or false: **Gold** is used in **electronics** primarily because it has the best conductivity.

Answer 38

False ## Footnote Gold is used because it resists corrosion, not because it has the best conductivity.

Question 39

Why is **copper** preferred over **aluminum** for household wiring?

Answer 39

Copper **conducts better and is stronger** and less reactive than aluminum. ## Footnote Aluminum is lighter and cheaper, but oxidizes easily, increasing fire risk.

Question 40

Why is **aluminum** used in **power transmission lines**?

Answer 40

It has **good conductivity** and is **lightweight**. ## Footnote Despite being less conductive than copper, aluminum is cheaper and lighter.

Question 41

Explain why **silver** is the best **electrical conductor**.

Answer 41

Silver has the highest density of **free electrons**, making it the best conductor. ## Footnote Copper is more commonly used due to its lower cost and good conductivity.

Question 42

Why are **alloys** like nichrome used in heating elements?

Answer 42

They have **high resistivity** and can **withstand high temperatures**. ## Footnote The resistance of nichrome generates heat when current flows through it.

Question 43

# Fill in the blank: \_\_\_\_\_\_\_ is widely used as an **electrical insulator** in high-voltage systems.

Answer 43

Ceramic ## Footnote These resist heat and electricity, making them ideal for insulating power lines and equipment.

Question 44

Explain why **rubber** is a good **electrical insulator**.

Answer 44

Rubber has **tightly bound electrons that do not move freely**, preventing current flow. ## Footnote Insulators block or resist the flow of electricity.

Question 45

# True or false: **Glass** is a better insulator than **wood**.

Answer 45

True ## Footnote Glass has higher resistance to electrical flow than wood, especially when dry.

Question 46

# Fill in the blank: \_\_\_\_\_ is a superconductor at **cryogenic temperatures**.

Answer 46

Lead ## Footnote Lead becomes a superconductor below 7.2 K (-266°C).

Question 47

Name a **non-metallic** material with high electrical conductivity.

Answer 47

Graphene ## Footnote It is an allotrope of carbon with remarkable conductivity properties.

Question 48

# True or false: **Plastics** are conductive materials.

Answer 48

False ## Footnote Plastics are insulators and block current flow.

Question 49

Explain why **diamond**, a form of carbon, is an excellent **electrical insulator**.

Answer 49

A diamond has a **strong covalent bond structure** that tightly holds electrons. ## Footnote Its crystal lattice prevents electron movement.

Question 50

Why is **graphite** a conductor while **diamond** is an insulator, despite both being forms of carbon?

Answer 50

Graphite has **free-moving electrons** in its layered structure, unlike diamond. ## Footnote The bonding structure makes the difference.

Question 51

Name a common **household application** of insulators.

Answer 51

**Plastic coatings** on electrical wires. ## Footnote They prevent electrical shocks.

Question 52

# True or false: **Water** is a good electrical conductor.

Answer 52

False ## Footnote Pure water is an insulator, but impurities, ions, can make it conductive.

Question 53

What types of materials are typically used for **circuit board** substrates?

Answer 53

* Fiberglass * Epoxy resin ## Footnote These materials are insulating and heat-resistant.

Question 54

# Fill in the blank: \_\_\_\_\_\_ is often used for **high-frequency signal transmission** due to its low resistance.

Answer 54

Silver ## Footnote Despite its cost, silver's conductivity makes it ideal for certain applications.

Question 55

# Fill in the blank: \_\_\_\_\_\_\_-film resistors are often used to limit current in **electronic circuits**.

Answer 55

Carbon ## Footnote These resistors are inexpensive and reliable for many applications.

Question 56

What role do **semiconductors** play in **medical devices**?

Answer 56

They **power devices** like pacemakers, glucose monitors, and imaging equipment. ## Footnote They enable precision control and efficient energy use.

Question 57

Name a **natural material** with conductive properties.

Answer 57

Pyrite | (fool’s gold) ## Footnote Pyrite's conductive properties have potential applications in renewable energy technologies.

Question 58

How do semiconductors contribute to **artificial intelligence (AI)** technologies?

Answer 58

They **power advanced AI chips** for machine learning tasks in devices like smartphones and servers. ## Footnote Efficient processing enables faster and smarter AI computations.

Question 59

What is a practical use of **conductive polymers**?

Answer 59

They are used in **flexible electronics** like wearable health monitors. ## Footnote Conductive polymers combine electrical properties with material flexibility.

Question 60

Why is **copper** commonly used in **lightning rods**?

Answer 60

Copper is an **excellent conductor**, efficiently directing lightning strikes safely into the ground. ## Footnote Its high conductivity and corrosion resistance make it ideal for lightning protection systems.