Exam (elaborations)
MSE 2090 Exam 2 Questions with Complete Solutions
- Course
- Institution
MSE 2090 Exam 2 Questions with Complete Solutions
[Show more]
Content preview
MSE 2090 Exam 2 Questions withComplete Solutions
electron energy band - ANSWER-when atoms are in close proximity are perturbed and
form a band of closely spaced states
formation of electron energy band - ANSWER-sodium example)) valence electrons in a
isolated Na atom --> hypothetical Na4 molecule - the 3s band splits in 4 distinct states --
> Na solid - a continuum of closely spaced discrete states and 3s valence "band" is half-
filled
the splitting of an energy state is dependent on the - ANSWER-interatomic spacing
facts about valence and energy band - ANSWER--Fans out because they do not want
to occupy the same energy spaces
-Along the equilibrium interatomic spacing, there is an energy band
-Others are not as wide --> because they are not the valence electrons, they are
splitting as much
-Band structures are based on quantum numbers
-Band gaps do not have energy states in them, so we can not have electrons in them
a "continuum" - ANSWER-energy band structure at equilibrium spacing
band gaps are WHAT energy ranges - ANSWER-forbidden
why do we care about energy band structure? - ANSWER-the nature of this energy
band structure determines if a material is a conductor, semi-conductor, or insulator
fermi energy - ANSWER-is the highest filled state at 0K; related to valence structure
Metals have energy states adjacent to highest filled state at Ef. What are two ways this
can happen? - ANSWER-1. partially filled band
2. a filled band overlaps with an empty band
for what and what, the valence band is full and separated from the empty conduction
band - ANSWER-semiconductors and insulators
insulator - ANSWER-- valence band is separated by a larger energy gap (>2 eV)
- ionic or strongly covalent
- ions, electrons, and holes
, semiconductor - ANSWER-- valence band is separated by a smaller energy gap (< 2
eV)
- weakly covalent
- electrons and holes
conduction in metals due to - ANSWER-free electrons
free electrons - ANSWER-electrons with energies > fermi energy (Ef)
conduction in metals - ANSWER-1. energy states within a band are VERY close
together (the lines & dots)
2. energy from electric field excites electron into conduction band
3. metals have high density of free carriers (electrons) --> HIGH CONDUCTIVITY
conduction in insulators and semiconductors due to - ANSWER-free electrons and
holes
the position of a missing electron; is treated as a positively charged particle
- charge is the same as electron but opposite sign (+1.6 e-19 C) - ANSWER-hole
larger band gap - ANSWER-insulators - more energy required to create "free charge
carriers" --> LOWER CONDUCTIVITY
true or false? higher temperature = more energy to excite electrons - ANSWER-true
are there holes in metals? - ANSWER-NO because do not jump a band-gap isolated to
a single or overlapping band
How do free charge carriers move and what affects their movement? - ANSWER-An
electric field exerts a FORCE on the FREE CHARGE CARRIERS
- electrons will accelerate in opposite direction
- holes will accelerate in the field direction
True or False? In a perfect crystal, electrons will continue to accelerate as long as an
electric field is applied, thus current would continually increase with time. - ANSWER-
False. Current reaches a constant value. Crystal is not perfect!! Imperfections lead to
FRICTIONAL FORCES!!!
drift velocity - ANSWER-when electrons reach a terminal velocity due to scattering
scattering - ANSWER-- electrical resistance comes from scattering
- causes: atom vibrations, impurities, structural defects (point, line, and planar)
- lower amount of scattering --> fewer impurities/defects --> more mobility
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller lectknancy. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $15.49. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
76799 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now