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Material chemistry > Dielectric materials week 6 > Flashcards

Dielectric materials week 6 Flashcards

1
Q

What is a dielectric material?

A

A dielectric material is an insulating substance that can be polarized by an electric field.

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2
Q

True or False: Dielectric materials conduct electricity.

A

False

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3
Q

Fill in the blank: The ability of a dielectric material to store electrical energy is characterized by its ______.

A

permittivity

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4
Q

What is the unit of permittivity?

A

Farads per meter (F/m)

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5
Q

What is the dielectric constant?

A

The dielectric constant is the ratio of the permittivity of a material to the permittivity of free space.

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6
Q

List one common application of dielectric materials.

A

Capacitors

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7
Q

True or False: Dielectric strength is the maximum electric field a dielectric material can withstand without breakdown.

A

True

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8
Q

What is the relationship between dielectric materials and capacitance?

A

Dielectric materials increase the capacitance of capacitors by reducing the electric field within the capacitor.

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9
Q

Multiple Choice: Which of the following is NOT a dielectric material? A) Glass B) Water C) Copper D) Teflon

A

C) Copper

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10
Q

What happens to a dielectric material when exposed to an electric field?

A

It becomes polarized, meaning that the positive and negative charges within the material are displaced.

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11
Q

Fill in the blank: The process of polarization in dielectric materials involves the alignment of ______ within the material.

A

dipoles

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12
Q

What is the effect of temperature on the dielectric properties of materials?

A

Temperature can affect the permittivity and dielectric strength, often decreasing the dielectric strength at higher temperatures.

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13
Q

True or False: All dielectric materials have the same dielectric constant.

A

False

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14
Q

What is the term for the failure of a dielectric material to insulate against electric stress (subjected to a high electric field)

A

Dielectric breakdown

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15
Q

Multiple Choice: Which material typically has a high dielectric constant? A) Air B) Rubber C) Water D) Wood

A

C) Water

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16
Q

What is dielectric loss?

A

Dielectric loss represents the energy lost as heat in a dielectric material when it is subjected to an alternating electric field.

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17
Q

Fill in the blank: Dielectric materials are often used in ______ to store electrical energy.

A

capacitors

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18
Q

What is the primary function of a dielectric in a capacitor?

A

To increase capacitance and store electric charge.

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19
Q

True or False: The dielectric properties of materials can change with frequency.

A

True

20
Q

What does the term ‘relative permittivity’ refer to?

A

It refers to the dielectric constant of a material relative to the permittivity of free space.

21
Q

Multiple Choice: Which of the following is a characteristic of a good dielectric material? A) High conductivity B) Low dielectric loss C) Low permittivity D) High temperature coefficient

A

B) Low dielectric loss

22
Q

What is the role of dielectric materials in insulators?

A

They prevent the flow of electric current and protect conductors from electrical leakage.

23
Q

What happens to the capacitance of a capacitor if a dielectric material is inserted?

A

The capacitance increases.

24
Q

Fill in the blank: The measure of a material’s ability to resist electric field is known as ______.

A

dielectric strength

25
Q

True or False: A higher dielectric constant means a material is a better insulator.

A

False

26
Q
A
27
Q

What is a ferroelectric material?

A

A ferroelectric material is a dielectric material that exhibits spontaneous electric polarization that can be reversed by the application of an external electric field.

28
Q

True or False: All ferroelectrics are also piezoelectric.

A

True.

29
Q

Fill in the blank: The property of generating an electric charge in response to mechanical stress is known as __________.

A

piezoelectricity.

30
Q

Which of the following is a common application of pyroelectric materials? (A) Energy storage (B) Sensors (C) Insulation

A

B) Sensors.

31
Q

What distinguishes pyro- and piezoelectric materials from other dielectric materials?

A

Pyro- and piezoelectric materials can generate an electric charge in response to temperature changes and mechanical stress, respectively.

32
Q

What is the ideal electrical conductivity of dielectric materials?

A

Zero dc electrical conductivity

33
Q

How is capacitance defined in a parallel plate capacitor with a vacuum?

A

C0 = e0A/d, where e0 is the permittivity of free space

34
Q

What is the defining characteristic of non-polar dielectrics?

A

Centrosymmetric crystal structures

35
Q

What happens to dielectric materials at high frequencies regarding pliability?

A

Electronic polarisability dominates

36
Q

Define the Clausius-Mossotti relation.

A

It links permittivity and polarisability of a material

37
Q

What is a polar dielectric?

A

A dielectric with a dipole moment that can be modified in an electric field

38
Q

How do piezoelectric materials generate electrical energy?

A

By mechanical stress applied to them

39
Q

What does the term ‘hysteresis loop’ refer to in dielectric materials?

A

The relationship between electric field strength and polarisation

40
Q

What characteristic distinguishes ferroelectric materials from non-ferroelectric ones?

A

Ferroelectric materials can change dipole orientation in an electric field

41
Q

What happens to the dielectric permittivity when the temperature changes in pyroelectric materials?

A

It becomes temperature-dependent

42
Q

Which dielectric property describes how the capacitance of a material increases in the presence of an applied electric field?

A

Which dielectric property describes how the capacitance of a material increases in the presence of an applied electric field?

43
Q

What kind of structure do antiferroelectric materials have?

A

Adjacent dipoles arranged antiparallel, leading to zero net polarisation

44
Q

What is a primary application of piezoelectric materials?

A

In sensors and actuators

45
Q

What type of dielectrics can exhibit an anomalous increase in resistivity with temperature?

A

Certain ferroelectric materials, especially near phase transitions

Material chemistry (4 decks)

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