Materials: Topic 7, Electrical and Magnetic Properties

Question 1

What type of bonding has de-localised electrons?

Answer 1

Metallic

Question 2

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

Answer 2

Ionic

Question 3

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

Answer 3

Covalent

Question 4

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

Answer 4

Van-der-Waals

Question 5

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

Answer 5

Conductors (Metals)

Question 6

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

Answer 6

Insulators (Ceramics, Glass, Polymers)

Question 7

As temperature rises, does electrical resistivity increase or decrease?

Answer 7

Increase

Question 8

Are all polymers complete insulators? (0% conductivity)

Answer 8

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

Question 9

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)

Answer 9

Drude (See lecture 1 slide 16 for more info)

Question 10

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

Answer 10

Ionic

Question 11

What are the charge carriers in semi-conductors?

Answer 11

Electrons and Holes

Question 12

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

Answer 12

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

Question 13

Silicon is an example of a…

Answer 13

Semiconductor

Question 14

Coventry is an example of a…

Answer 14

Shithole

Question 15

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?

Answer 15

Small

Question 16

The band gap (E) for semiconductors is

Answer 16

E small than 3eV

Question 17

What type of atom structure does Silicon have?

Answer 17

Diamond

Question 18

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

Answer 18

Excitation

Question 19

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

Answer 19

P-type = Positive
N-type = Negative

Question 20

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

Answer 20

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

Question 21

What circuit component switches and amplifies signals?

Answer 21

Transistors

Question 22

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

Answer 22

No current flows.

Question 23

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

Answer 23

There’s twenty of them.

Question 24

Do dielectric materials reflect EM waves?

Answer 24

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

Question 25

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

Answer 25

Capacitor

Question 26

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

Answer 26

Permittivity (as well as Capacitance)

Question 27

When do piezoelectric materials go through polarisation?

Answer 27

When they are subjected to stress.

Question 28

When do pyroelectric materials change their polarisation behaviours?

Answer 28

When they are heated.

Question 29

How do ferroelectric fields reverse their polarisation?

Answer 29

When they are put into an electric field.

Question 30

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

Answer 30

FUCKING REALLY JACK. FUCK U DAN!

Question 31

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

Answer 31

Right hand grip rule (Wehay)

Question 32

Are magnetic field strength and magnetic flux directly proportional?

Answer 32

Yes

Question 33

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

Answer 33

The Permeability of the material.

Question 34

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

Answer 34

They orientate in the same direction.

Question 35

As temperature increases, magnetisation increase or decreases?

Answer 35

Decreases (until it reaches 0)

Question 36

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

Answer 36

Yes

Question 37

Is Dan going to pass this exam?

Answer 37

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

Question 38

What is a metamaterial?

Answer 38

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

Question 39

What is a refractive index?

Answer 39

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

Question 40

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

Answer 40

Reflects off the surface.

Question 41

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

Answer 41

Refracts through the surface.

Question 42

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

Answer 42

Superconductors

Question 43

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

Answer 43

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

Question 44

What is a superconductor by definition?

Answer 44

A material that conducts electricity without any resistance.

Question 45

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

Answer 45

Critical temperature

Question 46

How are superconductors used to levitate materials?

Answer 46

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

Question 47

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

Answer 47

Inversely proportional

Question 48

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

Answer 48

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

Question 49

Name some uses of superconductors.

Answer 49

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

Question 50

Fuck it I'm done.

Answer 50

Later bitches.