energy production Flashcards
energy density
energy per unit volume (MJ m−3)
specific energy
energy per unit mass (MJ kg−1)
2 mechanisms that convert heat to work
heat engine and turbine
how dyou convert mechanical to electrical energy
A generator consists of a coil rotating in a magnetic field (or a magnet rotating in a coil). According to Faraday’s law an emf is induced when the magnetic flux enclosed by the coil changes.
enrichment
processing of fuel to increase the amount of fissile nuclei (235U).
moderation
graphite used to slow down neutrons so they are absorbed (this does not slow the chain reaction but makes the reaction possible).
critical mass
the minimum amount of nuclear fuel needed for a chain reaction
meltdown
when the core of a reactor gets too hot and melts.
low level waste
radioactive waste produced during the processing of fuel and parts of the reactor that have become radioactive after exposure to radiation emitted by reactor.
high level waste
the spent fuel contains highly radioactive fission fragments. Needs to be kept away from humans for 100 000 years.
what does a solar heating panel do
absorbs radiation from the Sun and converts it into thermal energy.
what does a photovoltaic cell do
absorbs radiation and converts it into electrical energy.
what does a solar power station do
uses mirrors to reflect radiation to a central tower where water is boiled and used to turn a generator to generate electricity
oscillating water column
waves cause water to move up and down a column pushing air through a turbine which is connected to a generator
pelamis
cylinders connected by joints that bend when waves pass. Movement is used to pump a fluid through a turbine.
fossil fuels enhance greenhouse effect
use of fossil fuels increases the concentration of carbon dioxide in the atmosphere so more IR radiation is absorbed leading to an increase in the surface temperature
approx how much incident radiation is reflected off the ground?
30%
albedo
total scattered power (reflected) /total incident power
surface heat capacity (Cs) equation
Q/(A🔺T)
what is the stefan-boltzmann law and what is its use
P = A o T^4
used to calculate power radiated per unit area given temperature
emissivity
ratio of energy radiated by body/energy radiated by perfect black body at same temperature
wiens displacement law and use
peak displacement = 0.99289/T
used to determine the temperature of the sun from the peak in the spectrum
solar constant
the power per unit area at the earth (1400Wm^-2)
ultraviolet radiation interaction with atmosphere
absorbed by ozone layer
infrared radiation interaction with atmosphere
excites molecules of water, methane, and carbon dioxide (greenhouse gases)
after absorption energy is re-emitted in random directions
interaction between visible light radiation and atmosphere
mostly passes through
how can a wood burning stove be made more efficient
circulate the waste gases through a system of pipes, transferring heat energy to stones that retain the thermal energy long after the fire goes out
katabatic winds
formed when a high pressure is caused by dense cold air pressing down at the top of a mountain, resulting in air flowing downhill
the sun
burning ball of gas fuelled by a dense hot core where hydrogen is fused to form helium
how tides work
- gravitational attraction between water in oceans and Moon causes water to bulge outwards on side facing moon and opposite side
- as Earth rotates these bulge travel around causing the two high tides
bodies with same temperature but lower emissivity difference in radiation emitted
same peak wavelength but less power
PN junction
slice of semiconductor where one side has been doped with impurities with holes and the other side impurities with electrons
what’s the energy from nuclear?
when a large nucleus splits into 2 smaller ones, the total binding energy increases, resulting in the release of ~100MeV of energy
fissile nuclei
235U
2 causes of meltdown
malfunction in cooling system
leak in pressure vessel
emissivity of a black body
1
black body
a hypothetical body that absorbs without reflection all of the electromagnetic radiation incident on its surface
why does the sun appear orange at sunrise and sunset
-the blue bit of the spectrum has been absorbed by the atmosphere because sunrise and sunset are further away so there’s more atmosphere to go through
why is it not possible to get all the energy from the nuclear fuel
when the amount of 235U falls below a certain value a chain reaction can no longer be sustained
control rods
used to slow down the reaction if it goes too fast
made of neutron-absorbing material eg Boron
why in theory would painting surfaces white decrease the greenhouse effect?
if more light is reflected from the earth then less energy is absorbed, so temperature will be less
renewable energy source
one where the use/depletion of energy source is less than the rate of production/regeneration of source
how does anti-reflective layer in photovoltaic cell work?
light reflecting off top layer of very thin film undergoes a phase change of pi whereas light reflected off the bottom layer doesn’t. The reflected light therefore interferes destructively reducing energy loss.
fuel
chemicals that when burnt release energy in the form of heat
what changes the solar constant?
1) how much energy the sun is giving out (more sunspots means more energy)
2) distance between earth and sun (orbit elliptical so orbital radius changes)
what makes materials different colours
whether a particular wavelength photon is absorbed or reflected by the material
what makes smth red
reflects red photons but absorbs other colours
why are black bodies black
cos they absorb everything they don’t reflect any photons
average surface heat capacity of earth (not in data booklet)
4x10^8Jm^-2K^-1
why does steam being released onto the blades of the turbine cause it to rotate
the change in momentum of the molecules will result in a force on the surface
what is a generator and how does it work
a generator consists of a coil of wire in a changing magnetic field.
The changing magnetic field creates an emf in the coil, causing a current to flow in the load resistor
energy change in generator
mechanical to electrical
how does the anti-reflective layer of a photovoltaic cell reduce energy loss
Light reflecting off the top layer of this v. thin film undergoes a phase change of pi whereas the light reflected off the bottom layer does not
-> the light therefore interferes destructively, reducing energy loss
stefan-boltzmann law in words
power per unit area is proportional to the temperature^4
4 reasons why most of the world’s energy consumption is provided by fossil fuels
1) wide availability
2) ease of transportation
3) power stations can be built close to the source
4) high energy density
energy density
The energy that can be liberated per kg
what is the effect on the emission spectrum of increasing the temperature of a back body?
> total power radiated increases
> peak wavelength of radiation decreases
3 markscheme points re moderator
1) neutrons have to be slowed down (before next fission);
2) because the probability of fission is (much) greater (with neutrons of thermal energy);
3) neutrons collide with/transfer energy to atoms/molecules (of the moderator);
trillion standard form
10^13
surface area of earth
5.1x10^15
surface heat capacity
heat energy needed to raise 1m^2 of SA of a planet by 1*C
