Exam 3 Flashcards
Rules the engineer must follow for systems
- On r a sys is specified, it cannot be changed midway through calculation
- Boundary can be any shape, but it must be closed in space and time
- Boundary can be rigid (defining the volume of a space) or flexible (defining an object)
System
A particulate subset of the universe specified in time and space by a boundary
What is energy?
“The capacity for doing work”
Unit of exchange
1st law of thermodynamics
“Law of conservation of energy”
Energy can neither be created or destroyed
Energy can only be transformed
Work can be converted into…
- Another form of work
2. Heat
Energy accounting
Ef - Ei= input - output
Accumulation= net input
State quantities= path quantities
Kinetic energy
Energy associated with motion
Ek= 1/2mv^2
Potential energy
Energy associated with:
- position, either against a field (ex. Gravity, electric field,
- compressed spring, or
- stretched rubber band
Internal energy
U
Energy associated with atoms
Ex. Temperature, phase changes, or chem reactions
Work
Energy flow due to a driving force (not temperature)
- Mechanical (hydraulic)
- Electrical
- Photonic (solar PV)
- Cardiovascular
Heat
Energy flow due to temperature change
Ex. Conduction, radiation
Mass
Energy flow due to mass crossing the system boundary
Ex. Fuel
E= mc^
Universal accounting equation
Change= energy at Ti - energy at T
ΔEk+ΔEp+ΔU= (Win-Wout)+(Qin-Qout)+(Min-Mout)
Work input (Win)
Work done ON the system from its surroundings
Work output (Wout)
Work done BY the system to its surroundings
Form for heat and mass
Energy added to the system - Energy removed from the system
Work=
W= FΔx
Equation from joules experiment
ΔU= Won
t initial
Ek= 0
Ep
t initial
v> 0
Ek= 1/2mv^2
Ep
t initial
Ek= 0
Ep
2nd law of thermodynamics
Naturally occurring processes are directional
Closely tied to idea reversibility, but reversible processes have no directionality
Entropy
Electricity ➡️ light
Lightbul
Electricity ➡️ heat
Hair dryer
Chem energy in gas ➡️ torque on shaft
Gas engine and transmission
Power train
Cham energy in food ➡️ locomotion
Muscle movement
Krebs cycle
Natural gas ➡️ electricity
Gas turbine
Generator
A system converts….
Energy from one firm to another
Process not always perfect
Waste us usually heat
Efficiency
Measure of how well a system can convert energy
η= output/input
Percentage
Cascaded conversion
Can connect multiple systems together and do several conversions
Overall efficiency
Treat multiple conversions as a single process
ηoverall= E4/E1= η1η2η3
What has the smallest unit of charge?
An electron
Flowing charge is…
Current
Accumulated charge is…
Voltage
Metallic bond
Electrons are shared
Valence electrons form “cloud” or “sea” of electrons
Electrons are free to flow (because loosely bond and shared)
Causes metals to be good conductors
Electrical insulators
Electric charge does not flow freely
High resistivity
Plastic, polymer, ceramic, glass, paper, rubber
Current
Flow of positive electrons
Opposite of electron flow
1 coulomb is the charge of how many electrons?
6.24*10^-19
1 amp equal
1 coulomb glowing through a wire in 1 second
A= C/s
Current always flows…
Through
Electrostatic force
Gives rise to stored energy
F= (1/4πε0)(q1q2/r^2)
ε0= 8.854*10^-12 C^2/Nm^2
Energy
“The stuff that gets work done”
Unit of exchange like money
Power
Rate at which energy flows from one place to another
Units: J/s= W (energy per unit of time)
1hp= ___W
1hp= 745.7W
Voltage arises from
Accumulated charge being separated
Exists between two points
NOT an individual point
Voltage is a measure of…
How much energy each coulomb of charge contains
Difference between strength of electron supply and severity of electron shortage
1 volt=
1V= 1J/C
Relationship between power, voltage, and current
P= IV
DC
Direct current
Voltage and current are constant
Ex. All batteries, power supply in car
AC
Alternating current
Voltage and current alternating back and forth
Ex. Grid supplied electric power
Electricity is all about ______
Charge
Semiconductors
Modern materials designed to conduct only under certain conditions
Transistors, LEDs, amplifiers
In electricity flow through wire, electrons are induced by…
Chemical reaction in battery
How to calculate number of free/valence electrons?
(Volumedensity per mole)/(atomic massAvogadros number)
Positive terminal of battery=
Electron storage
Negative terminal of battery=
Electron supply
Resistance is caused by
Scattering and destructive interactions between atoms and electrons
Current
I
Quantity of electrons passing a point per unit time
Units: amps
Ohms law
V= IR
Resistance is present in…
All conductors
Kirchhoff’s first law
Current law
KCL
The algebraic sum of the currents flowing through a junction/node is zero
Sum of the currents flowing into a node= sum of the currents flowing out of that node
Node
Connection of 2 or more components
Kirchhoff’s second law
Voltage law
KVL
The algebraic sum of voltages around any closed loop in a circuit is zero
In series,…
Req= R1+R2+R3..
Current is constant
Voltage changes
Current flows out of…
Positive terminal of a source
Current flows into..
The positive side of a resistor
In parallel,
1/Req= 1/R1+1/R2+1/R3…
Voltage is constant
Current changes
Joules law
P= IV P= V^2/R P= I^2R
Digital/binary signal is made up…
1’s and 0’s
Base 2
How to represent 1’s and 0’s in binary
Voltage various conventions like TTL and CMOS
Why use digital?
Noise
Digital logic
Testing conditions by digital circuitry: the use if digital circuitry to determine if a condition is TRUE OR FALSE
What is digital logic founded on
George Boole
Boolean algebra
An algebra in which the binary operations are chosen to model the Union and intersection operations in SET THEORY
Operations of union
OR
+
Operations of intersection
AND
⚫️
Operations of complement
NOT
DeMorgan’s laws
!(x*y)= !x + !y !(x+y)= !x*!y
Path quantities include:
Work
Heat
Mass
State quantities include:
Kinetic energy
Potential energy
Internal energy
_____ is MVP to thermodynamics and engineering
Energy
How is energy distinguished?
By what it can produce
No mass or defining characteristic
Can be stored in a system
Broad definition of energy acc. to book
Ability to produce an effect or change on matter
Ultimate usefulness depends on…
How efficiently it can be converted
E=
Wd
Distance parallel with work
Unit of energy
Nm= J
Ftlbf
Potential energy is found with…
Datum plane
All matter is composed of..
Molecules that at a finite temperature are in continuous motion and have intermolecular attractions dependent on distance which = internal energy
Chemical energy
Energy released when fuel is burned or when food is consumed
Ex. Photosynthesis
Measured in terms of heat of combustion or heating value
Nuclear energy
Energy stored in atoms
Nuclear fission
Breaks nucleus into 2 parts and releases energy
Nuclear fusion
Combines light nuclei and releases energy (m➡️E)
What is needed to transfer energy?
Driving force or potential difference
What is a requirement for movement of an object against some resistance?
Energy
Electrical energy is a form of…
Work
Energy is transferred through conducting medium when there’s a difference in electric potential
What does circuit theory do?
- Provides smile solutions to practical problems with sufficient accuracy
- Allows us to decrease analysis of large systems to a series of small problems
- Is a means of SYNTHETICALLY (building up) complex systems from basic components
How do atoms combine?
By sharing their outer orbital electrons and thereby filling voids and establishing unique patterns if molecules
What keeps electrons orbiting around nucleus?
Attractive forces between protons and electrons
Atoms have a specific….
Lattice structure but vibrate around nominal positions
Electrostatics
Branch of science concerned with static/stationary charged bodies
Electric potential
Work required to bring like charges together at a certain point
Is the speed of electrons relatively fast or slow?
Slow
In a closed system , no _____ may cross the boundaries
Material/mass
But the boundaries may change shapes
During a cycle, there is no net change in _____
Energy
So Q= W
Ohms law is applicable at constant _____
Temperature
Reciprocal of resistance
Conductance (G)
G= 1/R
Measured in Siemens (S)
When several resistors are connected between the same 2 points they are in…
Parallel
