Energy And Electricity Flashcards
Where does wind come from?
It’s solar.
The earth continuously released into the atmosphere the heat received by the sun but unevenly
Types of renewable sources of energy
Nuclear Hydroelectric Waves Geothermal Biomass Wind Solar
How wind turbines work
- When the blades start moving, they spin a shaft that leads to s generator
- The generator consists of a conductor (ex. A coiled wire surrounded by magnets)
- The rotating shaft turns the magnets around the conductor and generates an electrical current
- Sensors cause the top of the turbine to rotate to face the wind and the blades change their angle to best catch the wind ️n the blades are flexible and stop spinning if there is too much wind
Wind miss application
- Wind turns the turbine blades
- Spinning the shaft
- Generating electricity
- An inverter converts electricity from DC to AC
- Electricity is connected directly to the mains power
- Or connected to a battery bank
- Or connected to the electrical grid
Advantages of wind energy
- Available and free
- Renewable
- Costs are decreasing
- No pollution
- Works all day/night
Disadvantages of wind energy
- Still uses land
- Wind fluctuates
- Mostly in rural areas
- Electricity storage?
Windmill packing density
As a windmill extracts energy from the wind, the turbine leaves behind it a wake characterized by reduced wind speeds and increased levels of turbulence
A turbine operating in the wake of a turbine will produce less energy and suffer greater structural loading
Rule of thumb: windmills cannot be spaced closer that ___times their diameter without losing significant power
5
Kinetic energy of a windmill
KE= 1/2ρAtv^3
Wind power density (per unit area and per second)
P= 1/2ρv^3
Power output from a wind turbine
P= 1/2(Cp)ρAv^3
Cp= the power coefficient= the fraction of the power in the wind that may be converted by the turbine into mechanical work
Where does solar energy come from?
Sun (a star)
Thermonuclear fusion
Entire EM spectrum
The amount of solar energy that reaches the surface of the earth every hour is greater than…
Humankind’s total demand for energy in one year
Non electric solar energy
Water heating Heating living spaces Day lighting Drying Agriculture
Solar energy generating electricity
Photovoltaics
Power tower
Concentrated and remote (ex. Asteroid rover)
About how much of the sun’s energy makes it to the surface of the earth?
47%
___% of solar energy comes from the middle 6 months
70%
Basics of solar powered water heaters
- Collector absorbs energy
- Heats water
- Water circulates (passive or active)
- Tank stores water
Color absorption
Dark colors absorb a lot and reflect a little
Light colors absorb little and reflect a lot
Power tower basics
- Collect light/energy from many reflectors
- Heat water
- Parabolic (parallel rays converge)
- Track the sun
Disadvantages of solar power
Inefficient and costly equipment
Part time
Reliability depends on location
Environment impact of PV cell production
A mill uses…
Mechanical rotational energy for work and processing
From water or wind
Breast shot wheel
One type of traditional water wheel
Overshot wheel
More efficient than breast shot wheel
What are dams for?
Recreation Drinking water Flooding Irrigation Energy
Hydroelectric power system
Flowing water is directed at a turbine (advanced water wheel)
The flowing water causes the turbine to rotate, converting the water’s KE to ME
The amount of electricity that can be generated by a hydropower plant depends on:
- Flow rate: the quantity of water flowing at a given time
- Head: the height from which the water falls
The greater the flow and the head, the more electricity produced
Standard equation for calculating energy production hydraulically
P= (head)(flow)(efficiency)*11.8
11.8= index that converts units of feet and seconds to kW kW= ft*ft^3/s*%
How useful is dam energy?
Moderate to high net useful energy yield
Fairly low operating and maintenance costs
Low pollution
Rarely shut down
Help control flooding
Supply a regulated flow of irrigation water to lowlands below the dam
Highest producers of renewable energy
Solar and hydroelectric
Disadvantages to hydroelectricity
Flood vast areas Destroys wildlife habitats Uproots people Keeps nutrients from settling downstream Keep fish from migrating upstream Kills lots of fish
What makes the tile floor feel colder than the carpet?
Thermal conductivity
Temperature
Quantitive measure of “hotness”
Described on the atomic scale
Vibrational KE
Measure of the INTENSITY of internal energy in a system
Heat
A measure of the total QUANTITY of thermal energy FLOW into or out of a system
Is the energy transferred between a system and its environment because of a temperature difference that exits between them
Joule determined…
The amount of work needed to produce one unit of energy
The equivalence between ME and internal energy (heat)
1 cal= __J
1 cal= 4.186J
Specific heat capacity
The amount of thermal energy needed to raise a unit mass of a substance a unit of temperature
Q
Energy in calories
Q= mcΔT
Specific heat
c
Different materials require different amounts of heat to produce the same temperature change
c= Q/(mΔT)
2 mechanisms for heat transfer due to a temperature difference
- Conduction
- Convection
- Radiation
Natural flow of heat is a,ways from….
Higher temperature regions to cooler ones
Conduction
Heat flowing through matter
Hotter atoms collide with cooler ones, transferring some of their energy
Direct, physical contact is required
Cannot occur in a vacuum
Poor conductors= insulators (styrofoam, wool, air…)
Convection
Energy transfer through the bulk motion of hot material
Ex. Space heater, gas furnace
“Hot air rises”
Radiation
Radiant energy: energy associated with electromagnetic waves CAN operate through a vacuum All objects Osborn and emit radiation Temperature determines: 1. Emission rate 2. Intensity of emitted light 3. Type of radiation given off Temperature is determined by the balance between rates if emission and absorption
Converting work into heat: Joule’s experiment
U= W Q= W mcΔT= FΔx mcΔT= maΔx
Thermal linear expansion
ΔL= L0αΔT
α= coefficient of linear expansion
Thermal volume expansion
ΔV= V0βΔT
β= coefficient of volume expansion β= 3α
Latent heat of fusion
(Solid/liquid)
ΔHfus (kJ/kg)
If T⬆️, melting point
If T⬇️, freezing point
Latent heat of vaporization
(Liquid/gas)
ΔHvap (kJ/kg)
If T⬆️, boiling point
If T⬇️, condensation point
Latent heat of sublimation
(Solid/gas)
If T⬆️, sublimation point
If T⬇️, sublimation point
Transition between phases is a _______ process
Constant temperature process
Melting/solidification: Qfus= mΔHfus
Boiling/condensation: Qvap= mΔHvap
Heat and combustion
Qcomb= mΔHcomb
Qcomb= energy released m= mass (kg) ΔHcomb= specific heat of combustion (MJ/kg)
Motors and engines yield…
Circular motion
Engines use
Combustion or steam
Motors use
Electricity
2 types of electric motors
AC and DC
2 types of DC motors
Separately excited
Self excited
Types of self excited motors
Series
Compound
Shunt
2 types of AC motors
Synchronous
Induction
Types of induction motors
Single phase
Three phase
Who designed the modern AC electricity supply system?
Tesla
Two wires carrying electric current…
Exert a force on each other (magnetic force)
Two wires carrying electric current in the same direction…
Attract
Two wires carrying electric current in the opposite directions…
Repel
Force, current, and magnetic field are all…
Perpendicular to each other
Righthand rule
A magnetic field of loops/coils with many “turns” is a ____
Solenoid
Magnetic field=
B= (210^-7)(N*I)/R
N= number of turns I= current R= radius in meters
A magnetic field coil is identical to…
Magnetic field of a disk-shaped permanent magnet
Reversing current in a magnetic field coil…
Reverses the polarity
Changes N and S
In a stationary (magnetic) field…
A permanent magnet is added
Electromagnet rotates and poles line up
Switch poles of electromagnet and it will rotate to line up again
Stationary part of motor
Stator
Permanent magnet
Rotating part of motor
Rotor
Electrically controlled “brushes” to change polarity and reverse rotation to rotate the shaft
Generator
Essentially a motor working in reverse
Electromagnetic induction
Power supplied by wind, water, or fuel
Electromagnetic induction
If you move a magnet near a coil of wire, a current will be produced
Other magnetic uses
Levitation
Transformer: power in-power out
