Studied by 3 people
gravitational contraction
the sun generates energy by slowly contracting in size, a gradually shrinking sun would always have some gas moving inward converting gravitation potential energy into thermal energy
sun has 2 kinds of balance that keep its size and energy output stable
gravitational equilibrium and energy balance
gravitational equilibrium
between outward push of internal gas pressure and the inward pull of gravity
energy balance
between the rate of which fusion releases energy in the sun’s core and the rate at which the sun’s surface radiates this energy into space
in about 5 billion years…
the sun will finally exhaust its nuclear fuel and gravitational contraction will begin once again
sunspots
visible splotches that appear darker than the surrounding surface (larger in life than earth)
power
the rate at which energy is used or released
luminosity
a stars total power output
solar wind
stream of charged particles continually blown outward in all directions from the sun
corona
outermost layer of the atmosphere, temp is astonishingly high, density is very low
cromosphere
middle layer of the solar atmosphere and the region that radiates most of the sun’s UV light
photosphere
lowest layer of the atmosphere, visible surface of the earth
convection zone
where energy generated in the solar core travels upward, transported by the rising of hot gas and falling of cool gas called convection
radiation zone
where energy moves outward primarily in the form of photons of light, turbulence of convection zone gives way to the calmer plasma
core
source of suns energy, density is more than 100 times that of water, extreme pressure
radiative energy
the energy that light carries
joules
the unit we measure energy in
power
the rate of energy flow, measured in units called watts
spectrum
a prism split light into the rainbows of light
white light
a mix of all these colours in roughly equal proportions
black light
when we perceive no light and hence no colour
primary colours of vision
red, green, blue (RGB)
how do light and matter interact
emission, absorption, reflection
transparent
materials which transmit light
opaque
materials that absorb light
particle
can sit still or move from one place to another
waves
consist of peaks
wavelength
distance from one peak to the next
frequency
number of peaks passing by any point each second
hertz
another name for cycles per second
field
describe the strength of force that a particle would experience at any point in space
electromagnetic waves
light waves are traveling vibrations of both electric and magnetic fields
photons
light comes in individual “pieces” that have properties of both particles and waves
electromagnetic spectrum
light that we can see
electromagnetic radiation
light itself
visible light
light that we can see with the naked eye
infared
light with wavelengths somewhat longer than those of red light
Ultraviolet
lies between blue and end of the rainbow in wavelengths
atoms
all ordinary matter is composed of atoms
element
atoms come in different types and each type corresponds to a different chemical element
atoms are made up off:
protons
neutrons
electrons
nucleus
attraction and repulsion
oppositely charged particles attract and similarly charged particles repel
molecules
number of different material substances is far greater than the number of chemical elements because atoms can combine to form molecules
chemical bond
interactions between electrons that hold the atoms in a molecule together
molecular dissociation
high enough temp, the collisions become so violent they break chemical bonds
pressure
force per unit area pushing on an objects surface
energy levels
the possible energy of an atom
energy level transitions
an electron can rise from a low energy level to a higher one, or fall from a high level to a lower level
spectroscopy
the process of obtaining a spectrum and reading the info it contains
three basic types of spectra
continuous spectrum
emission line spectrum
absorption line spectrum
continuous spectrum
the spectrum of a traditional, or incandescent, light bulb is a rainbow of colour, because the rainbow spans a brand range of wavelengths without interruption
emission line spectrum
a thin or low density cloud of gas emits light only at a specific wavelengths that depend on its composition and temp, the spectrum consists of bright emission lines against a black background
absorption line spectrum
cloud of gas lies between us and a lightbulb, still see most of the continuous spectrum of the light bulb, but the cloud absorbs light of specific wavelengths, so the spectrum shows dark absorption lines over the background rainbow
two laws of thermal radiation
each square metre of a hotters object surface emits more light at all wavelengths
hotter objects emit photons with a higher average energy
doppler effect
if an object is moving toward us the light waves bunch up and its entire spectrum is shifted shorter wavelengths
sun’s size
diameter is 100 times Earth’s diameter
sun’s distance
8 light minutes from Earth
Cecilia Payne-Gaposchkin
showed that the sun was made mostly of hydrogen, a little helium, and tiny amounts of other elements
colour and wavelength
the wavelength of light determines its colour and energy
short wavelengths
bluer (and more energetic)
red light
low energy (700 nm)
blue light
high energy (400 nm)
the sun appears to have
a continuous spectrum: it has some of every colour of light
opaque objects
emit a special kind of continuous spectrum
blackbody spectrum
the amount of light given off by a blackbody and the wavelength where it emits the most light set by the temp of the blackbody
as you heat an opaque object
it emits more light
as you heat a blackbody
the wavelength at which it emits the most light shifts to shorter wavelengths
spectral lines
tell us what the sun and other stars are made of
electrons can be forced to jump to a higher-energy orbital by
absorbing light
different chemical elements have
different sets of orbitals
electrons can spontaneously drop to a lower-energy orbital by
emitting light
orbitals do not have colours but
transitions between orbitals do
stars are
blackbodies or “thermal emitters”
sun is not
on fire, it is mainly made of hydrogen
plasma
a gas that is so hot, the electrons break free from the atoms
hydrostatic equilibrium
the sun is in this, the pressure pushing outwards and the gravity pulling inwards is balanced
sun’s surface temperature
5800 K
sun's core temperature
15 million K
E = mc^2
the reaction between energy and mass
nuclear reactions can
convert matter to energy (or the reverse)
in the centre of the sun,
hydrogen is being converted into helium via nuclear fusion
nuclear fusion
providing enough outward pressure necessary to support stars against collapse
neutrinos
only interact with other matter via the weak nuclear force and gravity, can pass through objects that are very large and dense
neutrinos dont
respond to the electromagnetic force, so they dont interact with most matter
Note 
Flashcard (41)