Karteikarten

P7

blueaweiss Englisch 140 Karten

Karten in diesem Stapel (140)

1What is a solar day?A solar day is the time that passes between the sun appearing at its highest point un the sky on two successive days.
2Describe the apparent motion of the moon and the stars through the sky?The earths daily rotation make the moon appear to be traveling across the sky from east to west - but the moon is also orbiting the earth. The orbital moon takes longer than 24 hours to return to the same position in the sky. Thus the moon rises later every day.
The stars also appear to move across the sky. A long shutter sped of stars blurs movement into arcs. The stars take little less than 24 hours to return to the same position in the sky.
3What is a sidereal day? Why is time taken for a star to be in the same position slightly less than 24 hours?Because it actually takes 23 hours 56 mins and 4.09 seconds for the earth to rotate through 360 degrees. This is known as a sidereal day. It is different from a solar day because of the earth orbit around the sun. By the time the earth has turned through one complete revolution , it has also moved relative to the sun.
4Explain this in terms of an image?
5Explain the phases of the moon? and how do we see the moon?We see the moon because it reflects the sun's light. As the moon moves it reflects, more or less might towards the earth. We see the sunlit part of the moon change shape from a full circle to a crescent and back again. These shapes are known as the phases of the moon.
6Explain this in terms of a diagram?
7Explain the orbit of the moon?The moon takes 27.3 days to orbit the earth. But because the earth is moving around the sun, it takes the moon a bit longer to get back to the same position relative to the sun. In fact there are 29.5 days between two full moons. This is known as a lunar month.
8What is an eclipse (explain both types) and how does it happen?Moon and sun appear to be the same size in the sky due to difference in distance from us and size. As the moon orbits it sometimes passes between the sun and the earth, casting a shadow on the earth. This is called a solar eclipse.
When the moon travels into the earths shadow, it can no longer reflect the Sun's light and observes see a lunar eclipse.
9Explain a solar eclipse in terms of an image?
10Explain a lunar eclipse in terms of an image?
11Why is there not a solar eclipse each month? surely each time the moon moves between the sun and earth there would be one? describe an image that shows why not?
12Which plantes can be seen with the naked eye and what does the amount of light that a planet relicts to earth depend on?Up to saturn can be seen with the naked eye.
The amount light reflected depends on: how close the planet is to the sun, how close the planet is to the earth, the size of the planet, nature of the planets surface.
13What is retrograde motion? and what ddid this mean in terms of the previous model of the earth?When a planet in the sky appears to go backwards. This was pretty much unexplainable using an earth central model. The earth central model could explain the movement of the sun, moon and stars and felt intuitively correct but it couldn't explain the motion of the planets, nor why they varied in brightness.
14Explain the retrograde motion?The planets closer to the sun mover faster than the outer planets do. So when the earth, for example overtakes mars, it appears to go backwards.
15Explain summer and winter stars? what are constellations?Constellations are patterns in the stars. We see different stars in the summer from the winter because the earth has moved to the other side of its orbit around the sun. At night we are looking away from the sun into the universe.
The winter sky may seem more impressive because the nights are long and there are some very bright stars on show - but it is the summer that we see more stars. In the summer months our night skies aim towards the centre of the galaxy. The hay look to a clear summer sky is the billions of stars in the central disk of our galaxy.
16How do we locate stars?With two pieces of info: direction to face and how high to look up. The height of the star in the sky, above the equator, is given as an angle called the declination (dec). A negative declination means that the star is below the equator.
A star directly above the equator will have a declination of 0(degrees). The pole star (directly above the north pole) has an angle of about 90 degrees.
The angle that defines direction (east - west) to look is called the right ascension (RA). These two angles form a coordinate system for locating or describing the location of a star.
17Explain a diagram that shows this?
18What is the celestial sphere? what do we use it for?When you look at the night sky, imagine an invisible dome stretching over you. The light from every astronomical object is projected onto this dome. Together with the skies of the southern hemisphere, this form the celestial sphere. The celestial sphere has a north pole directly over the Earth's North Pole and an equator one the earth equator.
We use the celestial sphere as a reference for the coordinate system.
19How is the declination and ascension measured in the celestial sphere?The declination is measured from the celestial equator, in degrees, minutes and seconds. One minute (1') is equal to 1/60 of a degree. One second (1'') is equal to 1/60 of a minute.
Although it is an angle the right ascension is measured in units of time: hours, minutes and seconds. The celestial sphere rotates with the earth once every 24 hours, so 24 hours is equivalent to 360 degrees. Therefore one hour = 15 degrees.
20What is the ecliptic in a celestial sphere and what does it show?The plane of the earths orbit, the ecliptic, and is shown on the diagram on the next card. Viewed from the earth, the ecliptic shows the path of the sun during the year. The right ascension is measured from the point where the sun moves to the northern hemisphere. This is the spring or vernal equinox and it happens around march every year.
21Explain this in terms of a diagram?
22What is refraction and what does this mean for waves?When light or any other wave comes into a more dense material it travels slower. The sped of a wave depends of the medium in which it is traveling. As waves slow down they get closer together, in other words the wave length decreases. This is called refraction. However refraction does not change the frequency of a wave.
23In terms of refraction what happens at the boundary between two materials when a wave hits at an angle?Refraction cause the wave to change direction. When travelling into a medium where the speed is lower, it is like a car driving into mud. The wheel that hits the mud first slows down first and the car changes direction. If light passes from air through a glass block, it will change direction as it enters the block and again when it leaves. This because light travels faster in air.
24Give a diagram that shows the light and glass block example?
25In the diagram what does the line represent? and what is the line drawn at right angles to the block called? and which direction does refraction cause light to deviate towards?Line represents one ray, Line drawn at right angle - normal, Refraction causes a ray of light to deviate towards the normal as it enters the glass, and away from the normal as it leaves the block.
26Explain bringing light to a focus?By shaping a glass block we can use refraction to bring light to a focus. A glass convex lens, which is thicker in the middle than at the edges, can refract light rays so that they come together or converge. Rays of light that strike the lens parallel to its axis will meet at the focal point or focus.
27Explain this in terms of an image?
28Explain focal length and the power of a lens? and what is lens power measured in?Focal length is the distance from the lens to the focal point. A lens is more powerful if it has a shorter focal length (it can converge light in a shorter distance)
Dioptres (D)
29What makes a lens more powerful?Making the face of a lens more curved.
30What is the principal axis?The line through the centre of the lens.
31Why does a star look like just a point/ dot and what happens as objects get closer to us?The rays from a star are so far away from us the rays reaching our eyes become almost parallel. If the object is closer to us though the angle of light reaching the eye will be bigger.
32Explain this using a diagram?
33What happens if the light coming in is not parallel with the principal axis?The focus will be away from the axis.
34Explain this using a diagram?
35What are objects that look larger than a point called (they may include moons, suns, or galaxies)?Extended objects
36On a ray diagram how do we represent an object? and where do rays leave the object from? how do we represent the lens?An arrow from the principal axis. The tip of the arrow. The lens is a vertical line though the principal axis.
37Although rays leave the object in every direction which three directions can we plot accurately?1) the ray that hits the lens parallel to the principal axis will be refracted through the focal point
2) a ray that travels through the through the focal point will be refracted parallel to the axis (the reverse of ray 1)
2) A ray that hits the centre of the lens will be undeviated.
3) a ray that travels through the through the focal point will be refracted parallel to the axis (the reverse of ray 1)
38Show this in tens of an image?
39Where wil the focused image be formed?where the rays meet again.
40Explain the simple telescope? (in terms of order of components) rest is on next card.A simple telescope can be made from two convex lenses: the objective lens and the eye piece. The objective lens has a long focal length (low power) and the eyepiece has a short focal length (high power). The lenses are placed so that the length of the telescope is the sum of their focal lengths.
41Explain the objective and eyepiece in more detail?The objective lens has a larger diameter that the eyepiece. The objective needs to have a large area to collect more light and make a brighter image. The objective forms an image of the object at its focal point.
The eyepiece is smaller than the objective, but has a greater power. The eyepiece is ted ilk a magnifying glass to look at the image formed by the objective. Your eyes see a magnified image.
42Explain what happens when we look at an object far away, in terms of our eye?When we look at a distant object such as a star, your eye refracts the parallel rays of light to form an image on your retina at the back of your eye. We can say your eye is focused in infinity, as the source of the parallel rays is effectively at an infinite distance from your eye.
43What happens to the image of a distant object when we look through a telescope? and explain magnification?When you look at a star the same star you looked at with the naked eye, with a telescope, parallel rays enter your eye so your eyes is still focused on infinity.
The effect of the telescope is to increase the angle between the light rays and the axis of the the telescope. If you look at the diagram a few cards back the angle b is bigger than the angle a. This increases the apparent separation between stars and makes extended objects seems bigger.
If the object is made to look twice as big we say the telescope has magnification of 2. The magnification is equal to the ratio of the angles (b/a in the earlier diagram)
44Explain this in terms of an image?
45If you had a telescope made using a lens of power 2D as the objective and one of power 10 d as the eye piece what would the magnification be?The focal lengths of these lenses would be: objective lens, f= 1/power = 1/2 = 0.5
eye piece, f= 1/power = 1/10 = 0.1m
so magnification would be M= f(o)/ f(e) = 0.5/0.1= 5x.
46Why are telescopes described as light buckets and why do they need these features?Reflecting telescopes are open - topped cylinders with a highly polished mirror at the bottom.
The reason for this is, is if you want to see a faint star you need a larger aperture (hole in the top of the cylinder).
Light from distant stars had been spreading out for billions of kilometres in all directions so by the time it reaches earth it is very faint. A large aperture telescope collects more light, thus enough light to create an image.
47Describe the reflecting telescope?A reflecting telscope has a concave mirror to receive the light, rather than refracting it. The concave mirror is the opposite shape to the convex lens - though it caves in it has the same effect on the light as a convex. A concave mirror converges parallel light towards a focal point. A secondary mirror reflects the light through the eyepiece.
48Describe this in terms of an image?
49What are the problems with a refracting telescope?A refracting telescope (lens) needs to have a large objective lens if it is to form a detailed image or show giant objects, but it is difficult to manufacture such large lenses. The two curved faces have to be perfectly shaped. Such a lens will be heavy and can only be supported around the edge.
Also glass refracts light of different wavelengths different amounts, a refracting telescope produces an image with coloured edges. This is called chromatic aberration.
50Explain chromatic aberration in terms of an image?
51Why else do telescopes need to be large?Diffraction
52What is diffraction? and discuss the diffraction of light?When waves pass through a gap or round an obstacle they tend to spread out (diffract). Diffraction is greater when the gap, or the obstacle, is about the same size of the wavelength of the wave.
We don't normally notice diffraction of light as wavelength of light is smaller than everyday objects - but if we shine light through a very small gap the effect can be seen.
53Discuss an experiment that shows the diffraction of light?If you shine a narrow laser beam through a very narrow slit. The laser beam spreads out to form a central bright area (central maximum) which bright fringes on either side. I fate slit was narrower, the central maximum would get wider.
54Which factors affect diffraction?The wavelength of the wave (for a given gap or obstacle waves with a longer wavelength diffract more) , the diameter of the gap or obstacle (the diffraction is greater if the gap size approaches the wavelength)
55Explain diffraction in therms of the affect on an image from a telescope? talk about resolution.Light diffracts as it goes through a gap like the aperture of a telescope. The aperture is the objective lens or the mirror. If you are looking at a point of light, such as a star, diffraction will spread the light and you will see a bright central disc surrounded by circular fringes.
If two stars are close together it can become an issue as diffraction can cause them to smear making it difficult to decide if it is one or two stars. If we can't tell we say the image is not resolved. To improve resolution a bigger aperture is needed to overcome diffraction.
Also the larger the wavelength the worse the diffraction.
56How do we form a spectrum of visible radiation and why is this possible?Passing light through a glass problem. This is as the shorter wavelengths of light are refracted more than the longer wavelengths, the different colours that are present in the light become visible.
57What affects this? and what can this tell you?The colours that can be seen in a spectrum depend on the temperature and chemical composition of the light source. A star's spectrum can tell you how hot is is and what it is made of.
58What are diffraction gratings? why are they better than a prism?Astronomers use diffraction grating to produce spectra. A diffraction grating is made by drawing thousands of very closely spread lines on a reflecting plate. Light then reflects from the plate and the different wavelengths are diffracted by different amounts. The result is that specific wavelengths are visible from certain angles, thus producing a spectrum. Diffraction gratings produce a more evenly spread spectrum than a prism does and a reflective grating wastes very little light.
59What was the quasar problem and debate?A 'quasi- stellar-object' (quasar) was found but due to its spectrum baffled scientists who had no idea what it was. This is as compared to a star in our galaxy the light was highly redshifted. The redshift was moving faster than anything seen before (40 000 km/s).
This was a problem as according to current theories the speed of recession could only be seen if it was a very far from the earth. However the the object appeared to be 2.5 billion light - years away (too far to be observed from earth).
It seemed the object would have to be giving of huge amounts of energy, several times more powerful than a galaxy but the side of a solar system. Some scientists refused to accept this and suggested that the redshift was due to some other effect.
60What is are quasars now thought to be?Quasars are now believed to be the most distant objects in the universe. They are among the brightest, emitting enormous amounts of power despite being relatively small. The power is thought to come from matter as it falls into a supermassive black hole at the centre of a galaxy.
61What is parallax on a basic level?Using the apparent motion of the star as the earth moves around the sun to measure the distance to the star/ object. As the earth moves round the Sun, the nearby stars seem to move, compared to the background of distant star - which appear to be fixed. The closer the star, the larger is apparent movement.
62Describe the method to measure the distance to a star?To find the distance to a nearby star, you need two measurements. The position of the star compared to a distant star is measured twice; the reading are taken six months apart. The angle labelled p is called the parallax angle. The bigger the parallax angle, the closer the star is to earth. In practice the angle is measured by comparing two photos taken 6 months apart.
63What is parallax measured in?Measured in seconds of an arc (") 1 second is 1/60 of a minute, which is 1/60 of a degree. Angular seconds are often referred to as arc seconds.
64What is the parsec?The parsec is a unit of length defined using the parallax shift of a star. When the parallax is 1 second of arc, the distance to the star is 1 parsec.
Distance (parsecs) = 1/ parallax angle (seconds)
Parallax angles can get to small to measure however. The smallest angle one can measure is from the ground is about 0.02"
65What is the distance from the earth to the sun?1 astronomical unit (1 AU)
66What are light - years, parsecs and mega parsecs?Light travels at a constant speed in space, so we can use the time taken for light to travel between two objects as a measure of the distance between them. 1 light year is the distance travelled in one year.
Parsecs are 3.26 light years calculated using parallax. The distance to stars is measured is parsecs but the distance between galaxies is measured in mega parsecs (Mpc), that is millions of parsecs.
67What is luminosity and what does it depend on?The total power emitted by a star is its luminosity . This is the total energy emitted by the star in one second across all wavelengths and in all directions.
The luminosity depends on:
radius - larger stars have a greater emitting area (surface area) and therefore emit more radiation, surface temperature - the hotter the star, the more radiation it emits. The surface temperature also affects the colour of the star. Hotter stars burn blue white, cooler red.
68Explain apparent brightness?Light spreads out through space so a star further away will appear dimmer than a star that is closer even if it is actually brighter. The further the further the radiation spreads out - the dimmer it looks.
As the distance doubles the brightness goes to a 1/4 of its original levels.
Apparent brightness = 1 / distance squared.
69Describe this in terms of an image?
70Describe this in terms of an image?
71What is a variable star and what is a period?A variable star is a star that varies its brightness. Sine variable stars flash like a light house. The time taken to go through a complete period is called the period of the star.
72What was the previous and current explanation for variable stars?The previous was that, like the sun, have dark spots and when the star rotated it showed the darker or brighter side to the earth.
Current model a smaller star orbits a bigger star and once in its orbit eclipses the star changing the brightness. A binary star relates to this - when a bright star is orbited by a dimmer partner.
73What did Henrietta Leavitt find and what was her method?She was studying photographs of the Magellenic clouds, which are known to be nearby galaxies. She made a study of 177 variable stars. 45 of these were Cepheid variable stars which are large pulsating stars with brightness that changes in a predictable.
All the stars in her study came from the Mangellic cloud so Leavitt assumed they were the same distance away. Their brightness could then be compared fairly. Leavitt noticed that the brighter stars, the longer it took to go through its brightness cycle. By plotting a graph, she found a correlation between the brightness and the period of a Cepheid variable star.
74What are standard candles?If we know how much light an object emits, and how it bright is seems from Earth, it is possible to work out how far away it is. An object of known brightness is called a standard candle. A Cepheid variable star is a standard candle. If we measure its period, we can find its luminosity from Leavitt's graph. Then we measure the light that we receive on Earth. Comparing the two values allow us to calculate how far way it is.
75Describe the graph of luminosity against time and luminosity against period that Leavitt plotted?
76How did astronomers go about working out the shape and size of her galaxy?It is difficult to tell what the shape and size of our galaxy is from inside of it. Astronomers realised our sun was one of millions - it is spiral galaxy but 100 years ago there was no agreement on this or the size.
One method of measuring the galaxy was developed by Harlow Shapely. He used Cephied variable stars to measure the distances to groups of stars called globular clusters. He then made the assumption that all globular clusters were the same brightness and size, so he could measure distances further away, where no Cepheid stars were visible. Shapley suggested the milky way was bigger than people thought possible, and meat our galaxy would be the size of the universe.
77What are Nebulae? What do different astronomers think about them?Nebulae are patches of light in the sky that look fuzzy, bright clouds rather than points of light. By 1900 thousands had been discovered, some were spirals but there was a disagreement about what they were.
Some suggested that spiral nebulae were new solar systems being formed - each a spinning cloud of gas that would condos into a star and planets. Others thought - they were distant galaxies. Their nebulous appearance could be due to their enormous distance from earth. This was known as the 'island universe' hypothesis.
Others thought it was hard to believe their were other galaxies like ours as other evidence showed nebulae were quite small. Also when the Andromeda nebula got much brighter (we now know this was a supernova) it could not be explained by the 'island universe' idea.
78What was the Curtis, Shapely debate?When two astronomers debated the nature of nebulae. Heber Curtis argued for the 'island universe' hypothesis. He said spiral nebulae were galaxies like our own. He believed that our galaxy was only 30 000 ly across and that our Sun was near the centre of it.
Shapely thought our galaxy was much bigger, 300 000 ly across, and that it formed the universe. He believed that Sun was not at the centre of the galaxy and that the spiral nebulae were just clouds of gas, relatively small and nearby.
Neither had enough evidence to win.
79How did Hubble prove the Island universe hypothesis?Hubble discovered a Cepheid variable star in the Andromeda galaxy (by looking at photo's and realising a star in the nebulae varied in brightness). Over the next few weeks Hubble measured the brightness of the star, which varied with a period of 31 days. Such a long period meant a very luminous star, yet it appeared very faint here on Earth. Hubble realised that the star was very distant, at least one million light - years away. The star, and the nebula, were much too far way to be in our galaxy. The Andromeda nebula had to be a galaxy in its own right.
80Label globular clusters, galactic bulge, galactic disc and galactic centre?
81How do we know galaxies are moving away from us?The galactic spectra is almost always light is redshifted to the red end of the spectrum. This shows they are moving away.
82What was Hubble looking for and what did he find?He was looking for a link between a galaxy's distance and the speed at which it moves away from us (its recessional velocity). He looked for cepheid variables in other galaxies so that he could measure the distances. The further away the galaxy, the fainter the light that and the more difficult it was to find a cepheid variable that could be observed. However, after several years Hubble had enough results to publish. He found a correlation between a galaxy's distance and its recessional velocity. Hubble had discovered that the further away the galaxy, the faster it was moving away from us.
83What is Hubble's law? what does it show?Hubble's results lie close to a straight line through the origin. This means the recessional velocity, v, of a galaxy is proportional to its distance, d, from Earth. In other word, the speed of recession is equal to the distance multiplied by a number, called the Hubble constant.
It is measured in Mpc.
The fact the galaxies are moving away suggests, either: we are at the centre of the universe and the galaxies are repelled away or every galaxy is moving away from every other galaxy.
84Explain thermal radiation?If a piece of metal is heated it will first give off in fared. It will then glow and give off red then yellow then white light.
All objects emit electromagnetic radiation across a rang of wavelengths. The energy emitted at each wavelength depends on the temperature of the object. Hotter objects emit more energy at shorter wavelengths.
Stars behave like this -luminosity depends on its temperature. Hotter stars are more luminous and give off more shorter-wavelength radiation.
85On the next card explain the graph?this is an aid to next card
86—Shows emission emitted from three different stars. The curves show how much energy (vertical axis) is emitted at each wavelength (horizontal axis). The area below each curve shows the total energy emitted.
A relatively cool star (a), with temp 4200 not too luminous. Total energy emitted is low, as shown by the small area under the curve. The peak of the graph lies towards the red end of the spectrum, so tar glows orange red.
A hotter star © emits more energy, peak is in violet part. As star is emitting straggly all visible wavelengths, it will look blue white.
b - yellow.
87Explain energy transport in a star? and temperature? /structure?Nuclear fusion powers a star. This takes place within the core of the star. (where temp is around 16 million degrees C). The nuclear reactions release photons of gamma radiation that travel outward through the star. These photons of gamma radiation interact with atoms throughout the radiation zone.
Further from the core star gets cooler. The cooler gas us nice efficient in absorbing photons. The main energy transfer process in this region is convection. Regions of hot gas expand and rise towards the surface, where they lose energy, cool, contract and fall inwards again.
Surface of star is photosphere. This part we see. Energy emitted to space, mainly as electromagnetic (all wavelengths). Our suns surface (5500 degrees) means most radiation is visible part of spectrum.
88Describe the structure of the sun?
89Explain the emission and absorption spectrum? and how the two are linked?Emission line spectrum created when elements heated and light passed through a prism. Each element has unique spectrum.
Absorption - if a bright light shone through the vapour of an element, a spectrum forms with dark lines through it. Atoms of element had absorbed some of wavelengths of white light. The position of dark lines on absorption matches the position of coloured lines on emission.
90Explain both in terms of images?
91How can we analyse a stars spectrum, what does it tell us?A spectrum of the sun's light has hundreds of dark lines on it. These are caused by elements in the Sun's cooler, outer atmosphere, which can absorb different wavelengths of light. Every element has its own patter of absorption lines so, by analysing a star's spectrum, we can say which elements are present in the star.
Spectra can also reveal temperature. Some photos cause ionisation and create ions to form. The spectrum of an ion is different from the spectrum of the original atom, so astronomers can tell which atoms have been ionised. This gives a measure of temperature.
92—The sun's spectrum - careful analysis of lines can tell us which elements are present.
93How did Bohr explain the spectrums? and whats the background info?Light us emitted from an atom when an electrons lists energy. But spectrum shows only certain wavelengths emitted. Since colour depends of energy it shows electrons can only lose energy in certain amounts.
Bohr suggested electrons of an atom exist at certain energy levels. A photon of light is emitted when an electron drops from a higher to a lower energy level. Atoms of a particular element have unique energy levels, which lead to a unique set of energy jumps by electrons. Therefore only photons of particular energies are emitted. Higher energy of photon, higher frequency, thus shorter wavelength of light.
Absorption spectrum - dark lines arise as light has been absorbed by electrons in an atom. Only when light if of exactly right energy hits atoms can it be absorbed and electrons jump up to a higher energy level. That particular colour of light removed causing dark lines in spectrum.
94What is temperature, what causes pressure and what is absolute zero?Pressure caused by billions of gas molecules bumping and hitting against their surrounding/ walls - each exerts a small force on the wall and the total force = the pressure.
Temp not same as energy. Temp caused by average kinetic energy of molecules. If you heated air in room molecules would move faster. Kinetic energy of molecules increase - so would temp.
If we could find a way of continually cooling down a gas the kinetic energy would reduce. The molecules would move more slowly as temp dropped. Eventually stop moving all together. Temp could not get lower - absolute zero.
95Explain the relationship between temperature and volume?Imagine a piston pushing gown on gas in a container. It would be free to move but held in place by pressure from atmosphere. If though gas underneath piston heated the molecules would move faster and exert greater pressure and force on the piston pushing it up and increasing the volume of the gas. There is a linear relationship between the two. However not directly proportional as does not go through origin - volume of gas does not fall past freezing point.
96Why does using the unit Kelvin help to make this graph make sense and how do we find Kelvin?0 kelvin is absolute 0 so plotting a graph with it means the line now goes to the origin. In graph of volume against kelvin it is directly proportional. In the graph the horizontal line now shows absolute temperature. Thus V is directly proportional to T and v/t = a constant.
To find Kelvin add 273 to the temperature in degrees Celsius.
97Explain the relationship of pressure against temperature?If same experiment with piston carried out but piston was fixed, if volume could not increase pressure would. Thus a graph of pressure against temperate shows pressure is directly proportional to absolute temperate. Thus p/t = a constant.
98What is the symbol for direct proportionality?
99Explain the relationship between pressure and volume? describe and experiment?As volume decreases and the gas is compressed further and so hits the walls more often the pressure increases in a inversely proportional relationship. In an experiment with a pressure sensor and syringe it is important to keep factors like temp constant.
100What is Boyle's law? how can it be used?pressure x volume = constant
if pressure increases volume must decrease by the same factor and vice versa.
You can use Boyle's law to calculate new pressures/ volumes if old ones are known. E.g. if 20cm3 of air is trapped at pressure of 100kPa and syringe pushed to reduce to 5 cm3 you can use Boyle's law to find new pressure. If volume decreased by a 1/4 then pressure will have increased by factor of 4. So new pressure is 400kPa. Or you can use the constant itself (times the two together then divide the constant found by the changed number)
101What is pressure measured in?k/Pa - pascals
102What is an ideal gas?An ideal gas has molecules that take up a very small fraction of the gas's volume and which are too far apart to affect each other. A gas that is well above boiling point and not under high pressure will behave as an 'ideal gas'. All the laws only apply to 'ideal gas'.
103Re outline the three laws?pressure/ temp = constant (directly proportional)
volume/ temp = constant (directly proportional)
pressure x volume = constant (inversely proportional)
104Explain what giant molecular clouds are and what is going on inside of them (energy)?Where stars begin their lives. Mainly formed of hydrogen gas and interstellar dust, although there are small amounts of other particles such as helium, carbon and water.
Gravity is constantly acting to pull the molecules of dust together. As the cloud collapses, GPE becomes kinetic energy. Particles move faster and temp increases. Increase in temp --> increase in pressure. Eventually pressure of gas pushing outward is balanced by force of gravity pushing in. This cloud is now in equilibrium.
105What then happens to the giant molecular cloud and how does this form a protostar?Giant molecular clouds are not uniform; there are regions if higher density. These are less stable than rest of cloud. These clumps collapse into denser regions that will eventually become stars.
The dense regions of gas and dust are only stable while the gas pressure balances the gravitational force. The explosion of a nearby star (supernova), or a collision with another gas cloud can cause a gravitational collapse. Once again the gas becomes denser and hotter. The volume decreases and temperature increases, causing the outward pressure to increase until it balances gravity once more. By now the dense region has become so hot (2-3000 kelvin) it glows red - it is now a protostar.
106What then happens to the protostar?The protostar's gravity attracts more gas an dust onto its surface. OVer the course of a few million years the protostar becomes more massive. Eventually core becomes so hot and dense that nuclear fustian starts and a new star lights up.
107How are stars powered, what were previous explanations and what is the current one?Previous - early on scientist thought chemical reactions happening - sun made of carbon - burning like a fire. (meant sun could last 40 000 years)
Then thought powered by gravitation collapse - like protostar. (could last 25 million)
When realised mass can become energy helped scientists realise it was powered by nuclear fusion . Hydrogen nuclei are pushed together to form helium releases some of the binding energy.(could last 9.5 billion)
108Explain the core?The innermost 10% of the sun is the core. Conditions are extreme because of the enormous gravitational force. The density of the material in the core is 20 times that of iron, yet it still a gas due to the enormous temperature around 15 million kelvin. At this temperature there are no atoms just a plasma of electrons and nuclei. The sun is 78% hydrogen so most of the nuclei are just protons whizzing around at high speed.
109Explain fusion in a star in more detail (why its possible too) ?When two protons collide at such high sped they can fuse together, they undergo a nuclear reaction to form a deuterium nucleus: this is a heavy form of hydrogen. The high sped is important. Every proton carries a positive charge so two protons will repel each other. It is only when they collide at high sped that they get close enough for the attractive strong nuclear force to overcome the electromagnetic repulsion.
110What are the isotopes of hydrogen and how are the nuclei in fusion represented?Nuclei represented like atoms with mass (number of protons + neutrons ) and atomic number (number of protons).
Hydrogen isotopes: hydrogen 1 (ordinary hydrogen 1 proton) so ^1_1H, hydrogen 2 ( deuterium one proton one neutron) ^2_1H, hydrogen 3 (tritium one proton two neutrons)^3_1H
111What is the p-p cycle?A series of reactions that fuse hydrogen to helium, it starts with the fusion of two protons to make deuterium.
112Describe the reaction in terms of formula to form deuterium?
113Describe that reaction in terms of the mass and proton numbers? as well as charges?The has numbers on either side balance. The atomic numbers also balance which shows that the charge is the same before and after the reaction. Charge conservation is ensured by the production of a positron. The position is the anti matter equivalent of the electron. A positron has the same mass but opposite charge as an electron.
114What has happened to mass in the pp circle that seems to have disappeared?It has become energy.
115Describe the p-p chain in terms of an image?
116What did Fleischmann and Pons announce and what does this show about science?They had achieved fusion with simple apparatus. However announcement came before 'peer review'. Since though tried no scientist have replicated their results. This 'cold' fusion reminds scientists the importance of peer review.
117What is Einstein's equation?E=mc(2) where c = the speed of light. It explains what happens in a star and helps with calculations.
118What is the main sequence in a star?When a star is in equilibrium. The vast amount of energy released is fusion which heats the the core enormously causing enormous pressure as well as the pressure from the radiation released - pushing outwards on the rest of the star (which would otherwise cause the star to blast apart) is balanced by the the fact the mass of the star is great gravity holds it together.
This is the longest phase of a stars life, it will continue fusing hydrogen into helium for billions of years.
119What are massive stars? describe thenMassive stars have immense gravitational force at the centre. The temperature in the core is high enough to fuse larger nuclei together, despite the large repulsive forces. Helium nuclei are fused to make heavier nuclei such as beryllium, carbon and oxygen. This can continue until iron is formed.
The fusion of light nuclei releases energy but energy has to be supplied to form nuclei heavier than iron. Once the core stops releasing energy, the balanced forces keeping the star in equilibrium is lost and gravity will crush the star.
120What are, giant stars, supergiants and white dwarfs?Supergiants are huge emitting immense amounts of energy and are so hot they look blue.
Giant stars - Acrturus is slightly cooler than our sun but over 200 times more luminous they are also much much much larger
White dwarfs- sirius B has surface temp about 26 000 kelvin it emits mainly UV. It has about the same mass as the sun but size of earth
121Describe the Hertzsprung- Russell diagram?
122Describe in words the Herszprung Russell diagram?Shows the difference between stars. The luminosity of a star is plotted on the vertical axis, relative to the luminosity of the Sun. The surface temperature of a star is plotted on the horizontal axis, in Kelvin. Because the surface temperature determines its colour, the temperature axis also indicates the peak wavelength of light emitted by the star.
123Describe the three main groups of stars on the diagram?Main sequence - this diagonal line across the middle of the diagram contains stars in the stable part of their lives. All of these stars are fusing hydrogen into helium, but they cover a wide range go temperatures and luminosity's.
Supergiants/ giant stars - these groups contain stars that are much more massive than the sun. Some are coming to the end of their lives.
White dwarfs - theses are small hot stars where nuclear fusion has ceased. They will gradually cool and fade.
124What happens when the hydrogen runs out? what will happen to our sun?When a star runs short of hydrogen in its core, fusion is reduced. Less energy is released and the pressure drops. Gravitational attraction is now larger than the outward pressure so the stat contracts.
At this stage the core is mainly helium. Its surrounded by a shell of hydrogen. The gradational collapse raises the temperature and hydrogen fusion begins in the shell. The energy released by this causes the over layer of the star, the photosphere, to expand enormously. As the photosphere expands, its temperature drops and it shines red. When the Sun reaches this stage it will expand to a hundred times its current size swallowing up Mercury and Venus and become a red giant star. A red giant star has a cool photosphere and a hot, dense helium core. Its tremendously bright due to size. This phase is relatively short. The hydrogen in the shell will then begin to run out. What happens next depends on the stars mass.
125What is the formula for the formation of beryllium and carbon?
126Describe this in terms of an image?
127What is the final fate of stars around the size of our sun?The hydrogen fusion in the shell of the red giant produces more helium. This accumulates in the core, making it hotter and denser. When the temp = 100 million k, helium fusion begins. First beryllium then carbon are formed - further reactions then forms larger nuclei such as nitrogen and and oxygen. Stars with mass up to 8x the sun can't create the necessary temp for further fusion. When fusion stops the core collapses and the outer layers are ejected into space in a shell of material known as planetary nebula.
The exposed core is a hot spheres of carbon and oxygen knowns as a white dwarf. Its density is enormous - this then cools over millions of years which will form a black dwarf - the cold remnant of a star.
128Describe an HR diagram for the path of a star like our sun?
129What about giant stars?Stars with mass more than 8x of the sun are different. Extra gravitational force allows these supergiants to fuse heaver nuclei in their cores. Shells of carbon, oxygen and even heavier elements are formed. Eventually a core of iron and nickel is created.
Nuclear fusion of elements heavier that iron absorbs energy, rather than releasing it. The star can generate anymore energy. There is nothing to oppose gravity and the star undergoes a catastrophic collapse called a supernova. During a supernova the heavier elements are made. A massive shock wave rips apart, spreading the elements across space and leaving behind a dense core.
130What happens to the dense core?When the mass of the core is between 1.4 and 4 solar masses, gravity is so strong that protons and electrons combine to form neutrons. The core has become a neutron star. A neutron star is typically 20km across.
If the mass os created that 4 solar masses gravity is so strong no force can resist it. The core collapses further, its density increases and gravity gets even stronger. Eventually gravity is so strong that not even light can escape. A black hole has been formed. At the centre of the black hole, density and gravitational strength approach infinity. Nothing that enters the black hole can escape.
131How do we search for extrasolar planets?Too small to see directly - astronomers have to study the star they orbit. As a planet orbits its gravity makes the star wobble. Astronomers look for tiny changes in the stars position, or small changes in the colour of the star's light caused by the Doppler effect. Another way is to look for the small dip in light from a star as the planet moves between us and the star. So far no one has detected a planet like the earth.
132What is the Goldilocks zone?Many of the planets discovered so far away are unlikely to be homes for life as we know it. Massive planet's that orbit close to stars would be too hot and bathed in damaging radiation. A planet that is distance from the star will be too cold. The Goldilocks zone or habitable zone is a region where temperature is just right. Here water exists as liquid, something vital to life on earth.
133Why is it hard to find out about planets whats being done and why are scientists hopeful life does exist?NASA has proposed a project called terrestrial planet fining, which would look for signs of oxygen in the atmosphere of planets. To do this scientists would need to study the dim light reflected from the planet. However this would require a very expensive telescope 4x the size of Hubble's.
they are hopeful as so many billions of planets so must be some with life.
134What is SETI and what has been found out about Mars and europa?SETI - is listening for radio signals from advance civilisations but, so far, has found nothing.
Mars has some evidence of having liquid water in the past and some at NASA say they found fossils of bacteria (this is questioned)
Europa a moon of jupiter has ice (but maybe water below)
135Whats the argument for and against space based telescopes?For - Earth atmosphere absorbs some of light it reaches telescopes on the ground. It also causes unwanted refraction effects. Other wavelengths, such as X- rays, uv and in fared are absorbed by the atmosphere. Telescopes that observe the universe at other wavelengths have to into space. A telescope like JWST will be able to detect in fared radiation that would be blocked by the Earth's atmosphere.
Against - Some agains telescope like JWST. Some as ground based telescoped will be huge soon. Also space telescopes are expensive to launch and maintenance requires space walking astronauts.
136What are issues with telescopes on the ground and how are they overcome?Observing stars from the surface of the Earth involves peering through the atmosphere. Refraction distorts the image so the star appears to twinkle. Light pollution from streetlights or nearby towns reduces visibility and light pollution or bad weather can prevent observations all together.
Thus telescopes are put in remote places, as high above sea level as possible. The air has to be dry and free of pollution as water/ other particles will scatter the light. They are put where there are very few clouds.
137What is the advantages of compute control?Despite the remote locations of telescopes professional astronomers often work from offices. Telescopes far away can be controlled by a computer. The telescope will be steered and locked onto the object, tracking it as the earth rotates. The images re captured digitally by a charge coupled device. The digitised images can be studied in real time or enhanced and analysed by a digital computer. This can be shared between astronomers.
Remote access means astronomers can book time in different time zones and look at northern or southern skies. This is cost efficient.
Also ammeter astronomers can pay to have access - they have access to better telecopies than they could buy.
138What is the european planned ELT telescope?A very large telescope built in chile so its remote without pollution and will have little social impact. However workforce will have to be brought to site and road links will have to be made. Will be expensive and will need lots of energy.
139What are gamma - ray bursters and how are they going to be observed?There are busts of gamma ray radiation that no once can explain. They are random and last from fractions of a second to minutes. They sometimes have x-ray, uv or visible light afterglow.
One telescope made called swift will detect it then quickly swivel to see source. Then send co ordinates round world. Some may be put at right angle to examine after glow.
140How is the web being used?Telscopes produce millions of images a second - too much for astronomers to look at - being put online - public encouraged to examine.
One project called the milky way project looking for bubbles. THe bubbles indicate areas of active star formation. By putting tools and images online members of the public are encouraged to analyse and help us understand origin of stars.