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The atomic structure of sub-atomic particles and the electronic shells. It also explains the hydrogen emission spectrum and the Bohr Theory of Atomic Structure. The document further explores light sources, including broadband and narrowband light sources, and introduces diodes and semiconductors. It also discusses junctions and their effect on electrical current. useful for students studying mechanical engineering, physics, and electrical engineering.
Typology: Lecture notes
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w.wang
Wei-Chih Wang
Department of Mechanical Engineering
University of Washington
ME
When sub-atomic particles were first discovered in 1897, theywere thought to orbit the nucleus like planets orbit the sun.Unfortunately, this is the atomic model still taught in manysecondary schools. In the mid-20th. century, it was discoveredthat the structure of the electronic shells was somewhat morecomplex consisting of:- up to at least seven capital-lettered shells (1=K, 2=L, 3=M,4=N, 5=O, 6=P, 7=Q)- up to at least 4 small-lettered orbitals (s, p, d, f)- each orbital is further divided into sub-orbitals: s has 1, p has 3,d has 5, f has 7- each of these sub-orbitals can accommodate two electrons.
,Helium (He) withits two electrons,has filled its s-
The Hydrogen Emission Spectrum
The hydrogen emission spectrum is a
line spectrum
, i.e. only
particular frequencies (wavelengths, energies) are observed.
WHAT IS GOING ON HERE?
Atom in 'excited state', i.e. with increasedEnergy
H
2
2 H (energy)
Molecule
Atoms
H*
H + h
The excited atom returns to the 'normal' state (ground state) byreleasing the excess energy as electromagnetic radiation of energy(E= h
) corresponding to the energy difference between the
ground state and the excited state.The fact that the hydrogen emission spectrum is a line spectrum –only radiation of very specific frequencies being emitted – meansthat only excited states of very specific energies are being formed.
A theory was proposed to account for
these observations.
The Bohr Theory of Atomic Structure
- Quantum Mechanics
The
energy
of
electrons
in
atoms
is
In conventionalfilament lamps orlight bulbs, electriccurrent ispassed through acoiled tungstenfilament, containedin a glass envelopethat is filled with an
Halogen lamps arealso filament lamps.However, halogen isaddedto the fill gas toprevent evaporatedtungsten from
In a gas dischargelamp, once asufficient voltage isapplied, electrons areemitted from aheated electrode,creating a plasma ora gas capable of
high intensity discharge lamp (e.g.
metal halide lamp)
High pressure gasdischarge lamps emitradiation directly asvisible light. In thistype of lamp thecombination ofdifferent elementatoms in the hot gas
Wei-Chih Wang
University of Washington
Vaccum tube (i.e. type 2A3)
Thermistor
voltage
voltage
voltage
Diode
(i.e. PN diode, LED,laser diode, phtodiode)
(large negativetemperaturecoefficient ofresistivity)
Normalresistor
volt
current
curren
Ohm’s Law:
i=
1
T
D
nV v
S
D
e
I
i