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Design For Function > Materials: Topic 7, Electrical and Magnetic Properties > Flashcards

Materials: Topic 7, Electrical and Magnetic Properties Flashcards

1
Q

What type of bonding has de-localised electrons?

A

Metallic

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2
Q

What type of bonding is it when one atom gives an electron to another?

A

Ionic

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3
Q

What type of bond is it when two atoms share some of the same electrons?

A

Covalent

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4
Q

What is the other type of bonding that doesn’t involve any electron sharing?

A

Van-der-Waals

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5
Q

What is the name of something that allows electricity to pass through it (high conductivity, low resistivity)?

A

Conductors (Metals)

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6
Q

What is the name of something that doesn’t allow electricity to pass through it (high resistivity, low conductivity)?

A

Insulators (Ceramics, Glass, Polymers)

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7
Q

As temperature rises, does electrical resistivity increase or decrease?

A

Increase

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8
Q

Are all polymers complete insulators? (0% conductivity)

A

No. Some polymers have up to 25% the conductivity of copper.

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9
Q

What model is used to show electrical conductivity in metals, showing that electrons are the charge carriers in metals? (Unbound electrons that move in a straight line in a magnetic field surround nuclei)

A

Drude (See lecture 1 slide 16 for more info)

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10
Q

Cations and Anions are the charge carrier for what type of bonding?

A

Ionic

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11
Q

What are the charge carriers in semi-conductors?

A

Electrons and Holes

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12
Q

What type of diagrams are used to describe electrical conductivity in metals, insulators and semiconductors?

A

Energy Band Diagrams (the one the energy level of electrons)

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13
Q

Silicon is an example of a…

A

Semiconductor

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14
Q

Coventry is an example of a…

A

Shithole

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15
Q

If the energy band gap for metal is none and the band gap for insulators it is large, what is the gap size for a semiconductor?

A

Small

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16
Q

The band gap (E) for semiconductors is

A

E small than 3eV

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17
Q

What type of atom structure does Silicon have?

A

Diamond

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18
Q

In intrinsic semiconductors, what type of process creates an electron-hole pair in the structure?

A

Excitation

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19
Q

In extrinsic semiconductors, p-type and n-type dopants are added to carry charge. What type (positive or negative) does each one carry?

A 
P-type = Positive
N-type = Negative
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20
Q

P-n type junctions (combonations of both dopants) can be combined to form…

A

Devices (such as Transistors and Diode / Solid State Rectifiers).

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21
Q

What circuit component switches and amplifies signals?

A

Transistors

22
Q

In the positive direction, positive current flows through a Diode. What about in the negative direction?

A

No current flows.

23
Q

What’s the best part about having sex with twenty two year olds?

A

There’s twenty of them.

24
Q

Do dielectric materials reflect EM waves?

A

No. They store the energy inside of them because of polarisation mechanics.

25
Q

What circuit device’s material is polarised to store energy?

A

Capacitor

26
Q

The dielectric constant is the ratio of what between the material and a vacuum?

A

Permittivity (as well as Capacitance)

27
Q

When do piezoelectric materials go through polarisation?

A

When they are subjected to stress.

28
Q

When do pyroelectric materials change their polarisation behaviours?

A

When they are heated.

29
Q

How do ferroelectric fields reverse their polarisation?

A

When they are put into an electric field.

30
Q

What’s that film called with the snakes on a plane?

A

FUCKING REALLY JACK. FUCK U DAN!

31
Q

What rule is used to work out what direction the magnetic field acts in relation to the current in a coil?

A

Right hand grip rule (Wehay)

32
Q

Are magnetic field strength and magnetic flux directly proportional?

A

Yes

33
Q

The magnetic flux in a material divided by the magnetic field strength equals what.

A

The Permeability of the material.

34
Q

What happens to atoms of a conductor when they are in a magnetic field.

A

They orientate in the same direction.

35
Q

As temperature increases, magnetisation increase or decreases?

A

Decreases (until it reaches 0)

36
Q

Are magnetic materials used in transformers, motors and data storage?

A

Yes

37
Q

Is Dan going to pass this exam?

A

https://www.youtube.com/watch?v=5fc52FlDAm0

38
Q

What is a metamaterial?

A

A class of artificial material that show unique or exceptional properties not found in most other materials.

39
Q

What is a refractive index?

A

The amount an EM wave changes direction when it enters a material (like light in water).

40
Q

Permittivity (e) and permeability (u) define how a material reacts to electric and magnetic fields. It also affects what an EM waves does when it meets the material. What does the EM wave do if it meets a surface where e0 or e>0 and u

A

Reflects off the surface.

41
Q

What does an EM wave do if it meets a material where e>0 and u>0 or e

A

Refracts through the surface.

42
Q

Most metals have negative e but positive u. What type of material has positive e but negative u?

A

Superconductors

43
Q

Metamaterials can pass EM waves through them without them refracting or reflecting. What could be a potential use for them as a result?

A

Invisibility (can already be used to be invisible from radio and microwaves)

44
Q

What is a superconductor by definition?

A

A material that conducts electricity without any resistance.

45
Q

What temperature (and below) is the point where the resistance through it is 0?

A

Critical temperature

46
Q

How are superconductors used to levitate materials?

A

They reflect the magnetic field in a material and the force keeps it levitated.

47
Q

How are current, temperature and magnetic field strength proportional to one another?

A

Inversely proportional

48
Q

Why is it good for a superconductor alloy to have a high critical temperature?

A

Less coolant (usually Helium) is required to keep it at a low temperature.

49
Q

Name some uses of superconductors.

A

MRI Scanners, Maglev superfast trains, switches in mobile phones and efficient power transfer connections are the main uses.

50
Q

Fuck it I’m done.

A

Later bitches.

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