P8.3 Flashcards
What is the Doppler effect
The physical phenomena by which there is a change in the OBSERVED frequency/wavelength of wave, due to relative motion between observer and source.
How does the Doppler effect work - when the sound is moving towards you
When the sound source moves towards you…
… wave peaks move closer together…
… wavelength gets smaller…
… frequency/pitch of sound increases.
How does the Doppler effect work - when the sound is moving away from you
When the sound source moves away from you…
… wave peaks move further apart…
… wavelength gets bigger…
… frequency/pitch of sound decreases.
Why is the Doppler effect difficult to observe
- sound waves have a longer wavelength
- Doppler effect is observed when the relative motionbetween observer and source is very large…
… is observed for distant stars as they are moving very fast.
What is red shift
The shift in wavelength of the light from distant stars/galaxies to longer wavelengths.
What does red shifting imply
Implies that distant galaxies/stars are moving away from us
What is blue shift
The shift in wavelength of the light from distant stars/galaxies to shorter wavelengths.
What does blue shift imply
Implies that distant galaxies/stars are moving towards us
Evidence number 1 for the Big Bang - red shift
Light from distant galaxies is red-shifted.
The further away the galaxy, the greater the red-shift.
THIS MEANS
Galaxies are moving away from us.
The further away the galaxy, the faster it is moving away.
How does galaxies moving away from us at a faster rate (evidence 1) support the Big Bang theory
Thus, if galaxies are moving away from each other, this suggests that at one point, all matter must have been existed at a single point in space…
Define spectrum
the range of wavelengths (colours) observed when light from a source is separated into its separate wavelengths.
How does the spectrum provide evidence for red shift
The spectra of stars contains black lines.
These black lines correspond to very specific wavelengths of light absorbed by certain atoms in the star.
All stars contain Hydrogen and Helium atoms.
Hence all spectra from stars contain a series ofvery specific black lines (distinct pattern of separated lines)
These black lines are seen shifted in the spectrafrom distant stars towards longer wavelengths.
Implies light from distant stars has undergone a Doppler shift.
Galaxy A – it is further away, so is moving faster away from us.
Galaxy C is further away than both A and B.
Big bang evidence number 2 - Cosmic Background radiation - 3 steps
1 At the beginning of the universe, all the energy of the universe would have manifested as very short wavelength gamma waves.
- As the universe expanded, this gamma radiation would have stretched out to longer and longer wavelengths… and is nowMICROWAVE RADIATION.
- The fact that these microwaves uniformly/evenly fill the universe suggests they all started off from a single point(filling the universe as the universe expanded)
What are the 2 pieces of evidence for the Big Bang theory
- red shift
- Cosmic background radiation
How does Cosmic Microwave Background Radiation provide evidence for The Big Bang Theory? - 6 MARKS GO
- The Big Bang Theory states that all the matter and energy of the universe was concentrated at a single point.
- At the start of the universe, this energy was high energy gamma radiation.
- Since the universe has been expanding, these gamma waves have stretched out.
- They are now seen as longer wavelength microwaves.
- And are seen uniformly in all directions in the universe
- implying they all must have started at the same point
What is the sun
Star at the centre of the solar system.
What is a planet
Spherical bodies that orbit the Sun.
What is a moon
Spherical bodies that orbit planets.
What is a minor planet
Small spherical objects that orbit the Sun.
What is a comet
Dust/ice that orbit the Sun with long period, elliptical orbits.
What are the inner planets
Mercury, Venus, Earth, Mars
Characteristics of the inner planets
Rocky, have an atmosphere.(Mercury atmosphere very thin… Venus is hotter despite being further away from Sun)
What are the outer planets
Jupiter, Saturn, Uranus, Neptune
Characteristics of the outer planets
Gas giants / Ice Giants; rings and lots of moons.
What is the asteroid belt in our solar system
Pieces of rock left over from the formation of the Solar System; between Jupiter and Mars.
Our sun and the rest of our solar system was formed from the remains of a….
Supernova
Formation of our solar system - Part 1 ( forming a main sequence star)
ALL PLANETS HAVE THE SAME PART 1
- Clouds of dust and gas were pulled together by theforce of gravity.
- When enough gas and dust had gathered and became dense enough to start nuclear fusion, a protostar is formed.
- As protostar becomes denser and hotter
…… particles speed up
… particles collide more energetically
… nuclear fusion begins, forming a main sequence star.
Formation of our solar system - Part 2 ( forming a red giant OR a red super giant )
- A star is stable during its main sequence.
- radiation pressure outwards from nuclear fusion balances gravitational attraction inwards
- equilibrium / stability - Eventually the hydrogen nuclei will run out.
- star cools, radiation pressure drops
gravitational force collapses star, causing it toheat up again
fusion of heavier elements begins
… energy from fusion increases… radiation pressure increases
… star expands outwards
… becoming either a RED GIANT or a RED SUPER GIANT
What happens when the hydrogen nuclei run out in a main sequence star
star cools, radiation pressure drops
gravitational force collapses star, causing it toheat up again
fusion of heavier elements begins
… energy from fusion increases
… radiation pressure increases
… star expands outwards… becoming either a RED GIANT or a RED SUPER GIANT
Formation of our solar system - Part 3 ( following from a RED GIANT)
SMALL STAR
Nuclei for fusion run out
fusion slows down
radiation pressure decreases
gravitational force collapses star
heats up, becomes white dwarf
eventually cools down to form black dwarf
Formation of our solar system - Part 3 ( following from a SUPER RED GIANT)
LARGE STAR
Lots of heavier nuclei fused together torelease lots of energy
large increase in radiation pressure outwards
much larger than gravitational pull inwards
star explodes in a supernova
very dense neutron star forms
if neutron star is very dense, considered a black hole
Overall - low mass star life cycle
Overall - high mass star life cycle
Compare the inner and outer planets
Inner = mostly rocky
Outer = mostly gas
Inner = small mass, small gravitational fields, few moons
Outer = large mass, large gravitational fields, many moons
Explain why the sun started to shine
Once Sun became hot and dense enough under gravity, nuclear fusion of nuclei began, releasing energy, causing the sun to emit EM radiation and shine.
Explain why the sun is not expanding
There is a balance between the force of gravity inwards and the radiation pressure from nuclear fusion outwards, that ensures the Sun does not expand or contract.
Suggest why the outer planets have many more moons then the inner planet
Outer planets are larger (have more mass) than the inner planets.
Thus, their gravitational fields are stronger.
When the solar system was forming, the outer planets attracted more dust/gas towards them.
This dust/gas formed came together under gravity to form the many moons of the outer planets.
Suggest and explain why our sun will not become a black hole
Our Sun is a small star – doesn’t have much mass c.f. other stars.
Thus, when our Sun starts to run out of Hydrogen nuclei to fuse together, it will expand to form a RED GIANT.
Red giants eventually become black dwarves, never becoming black holes. Only massive stars (lots of mass) are able to become black holes at the end of their life cycles.
What is a satellite
any body that orbits a planet or star.
Examples of natural satellites
The moon is a satellite of Earth.Earth is a satellite of the Sun.
Examples of artificial satellites
Communications Satellites in orbit about Earth.
What is a geostationary orbit
satellite remains in a fixed position relative to the Earth
Orbital time of a geostationary orbit
24 hours
Orbital height of a geostationary orbit
36,000 km
Where is a geostationary orbit launched
Above the equator
Examples of geostationary orbits
Communications/GPS, television
What is a polar orbit
satellite rotates about the Earth once every 2 hours, as Earth rotates under it… satellite scans entire surface of Earth, very quickly.
Orbital time period of a polar orbit
2 hours
Orbital height of a polar orbit
2000km
Where is a polar orbit launched from
The poles
Examples of polar orbits
Weather, spy satellites
What determines the time period of an orbit
The velocity you launch a satellite at (in its orbit… not on the way up to space!) will determine the radius the satellite orbits the Earth at, and the time period of orbit.
How to get a small time period
High Velocity = Small Orbit Radius = Small Time Period
Explain why a geostationary satellite orbits in 24 hours.
Geostationary satellites are launched above the equator, and have an orbital velocity that ensures the time period of their orbit is 24hours.Thus, the satellite will always remain in the same position (in the sky) relative to the Earth.
Suggest why the Venus Express probe is not in a geostationary orbit
Probes are designed to scan the entire surface of a planet.
A geostationary orbit would keep the probe in a fixed position above Venus, and thus, the probe would only be able to image/scan a small section of the planet.
The probe would need to be a in polar orbit, with a small time period.
Definition of an elliptic orbit
its radius isn’t fixed.
What causes the centripetal force for a planet
The centripetal force for a planet is provided by the gravitational attraction of its star.
How do we know the centripetal force exists
A body in a circular orbit is constantly accelerating, as the direction of its velocity is constantly changing.
Hence, a resultant force must be acting upon a planet orbiting its star.
A resultant force that causes a body to performcircular motion is known as the centripetal force.
Why does the speed of a body never change in space
The centripetal force/gravitational attractionalways acts towards the centre of the circular motion/orbit.
The centripetal force on any bodyalways acts perpendicular to the body’s velocity.
Therefore, the speed of the body never changes!(just the direction)
What direction does the centripetal force act
always acts towards the centre of the circular motion/orbit.
always acts perpendicular to the body’s velocity.
If a satellite moves too slow…
… gravitational attraction will pull it in.
If a satellite moves too fast…
… gravitational attraction is not great enough to hold onto the body and it flies away.
How does distance from the orbit effect the time period
The further away a body is from the body it orbits, the slower its velocity needs to be to maintain a stable orbit = the longer its time period.
What happens when Charger particles vibrate
They emit EM waves
What happens if the charges ions vibrate faster
They emit EM radiation at a HIGHER frequency
The greater the temperature of a body… ( in terms of charges particles)
… the faster the particles vibrate… EM waves of greater frequency emitted
… therefore bodies that glow blue (high frequency) are….hotter than those that glow red (low frequency).
If a body absorbs more radiation than it emits…
Its temp increases
If a body emits more radiation than it absorbs,
It’s temp decreases
If the temp of a body is higher, does it mean the frequency is lower or higher
The hotter the body, the higher the frequency of radiation it emits.
Explain in terms of radiation why the temp of the earth is increasing
The Earth absorbs more radiation (via greenhouse effect) from the Sun than it emits back into space.
Explain why in summer with NO heating on, your house heats up in the day and cools at night
house absorbs and emits EM radiation.
During the day, it is hotter outside, so the house absorbs more radiation than it emits…
… which will cause the temperature inside the house to decrease.
During the night, it is cooler outside, so the house emits more radiation than it absorbs…
… which will cause the temperature inside the house to decrease.
Explain why hotter stars emit blue rather then red light
house absorbs and emits EM radiation.
During the day, it is hotter outside, so the house absorbs more radiation than it emits…
… which will cause the temperature inside the house to decrease.
During the night, it is cooler outside, so the house emits more radiation than it absorbs…
… which will cause the temperature inside the house to decrease.
What is the earths crust
a solid layer of rock about 50km thick.
What is the earths core like
Inner core - solid
Outer core - liquid
When does an earthquake occur
when forces inside the Earth become large enough to break and move layers of rock.
What types of waves do earthquake produce
Seismic Waves
What is the ‘focus’
The point where the Seismic Wave originates
What is the epicentre
The nearest point on the surface to the focus, is known as the epicentre of the earthquake.
What detects earthquakes
seismometers
What are P - waves
Primary Waves(P Waves)
Cause initial tremors lasting about 10 minutes
.
Longitudinal waves that push and pull the Earth
.
Can travel through solids and liquids.
What are S waves
Secondary Waves(S Waves) More tremors a few minutes later
Transverse waves that shake up and down the Earth
Cannot travel through liquids.
How do P and S waves travel
- P and S waves refract/bend slowly as they travel through the solid crust.
- At the boundary between the mantle and the outer core, the P and S waves refract a lot, because their speed suddenly changes a lot.
- S waves cannot travel through the liquid core,so are not detected on the other side of the Earth, producing S-wave shadow zones.
- P waves are refracted a lot as they cross the mantle/outer core boundary, also creating regions where they are not detected, producing P-wave shadow zones.
Compare P and S waves
P waves are longitudinal.
S waves are transverse.
P waves can travel through both solids and liquids.
S waves can only travel through solids.
Explain how seismic waves detected around the wir,d show that part of the earth is liquid
P-waves are longitudinal and can travel through solids and liquids.
S-waves are transverse and can only travel through solids.
Following an earthquake, P-waves are detected on the other side of the Earth, but S-waves are not detected.
This implies S-waves were unable to pass through part of the Earth.
Part of the Earth must therefore be liquid.
What does the waves bending as they travel in the earth imply
The Earth contains layers of different densities, such that boundaries between media exist, giving rise to refraction.[recall that just like reflection and diffraction, refraction is a wave phenomenon that only when waves cross the boundary between media]
