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AS and A Level: Waves & Cosmology

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  1. 1 When a source of waves is moving relative to an observer (either towards or away) the received waves have a different wavelength to the wavelength transmitted. This is known as the Doppler Effect and we can use it to calculate the speed of a galaxy relative to Earth.
  2. 2 Almost all galaxies show redshift, meaning that the wavelength received on Earth is longer than it was when transmitted. It’s called redshift because the wavelength received has moved towards tor even beyond the red end of the spectrum . Redshift implies that the galaxy is moving away from Earth.
  3. 3 Blueshift can be observed from ‘nearby’ stars and galaxies.

Hubble's law

  1. 1 Using redshift data from a number of galaxies, Hubble plotted a graph of recession velocity, v, against distance to the galaxy, d. This graph continues to be updated and it shows that v = Hod which is known as Hubble’s law. This means that the speed of recession is directly proportional to the distance to the galaxy.
  2. 2 Ho is the Hubble constant and it has a value of about 70 km s-1 Mpc-1, which is equivalent to 2.3x10-18 s-1. 1/Ho= 4.4 x1017 s = 1.4 x 1010 years! This is the age of the universe, about 14 billion years.
  3. 3 We can also find an estimate for the size of the (visible) universe, assuming that the maximum expansion speed is the speed of light. Using Hubble law, c = Hod so d = c/Ho = 14 billion light years.
  4. 4 The uncertainty over the value of The Hubble constant is becoming smaller as measurements of distance to galaxies improve
  5. 5 Since redshift is seen in every direction, the conclusion is that the universe is expanding.

Fate of the universe

  1. 1 The fate of the universe is closely linked to CRITICAL DENSITY. This is a theoretical density that would have enough mass in the universe to keep the expansion of space slowing down forever. The critical density is given by o= 3H2/8 . The universe would be FLAT. An accurate value for H is important, if we want an accurate value for the critical density. Note: H2 means that the percentage uncertainty in H has to be doubled.
  2. 2 If the actual density is greater than the critical density, then the universe will stop expanding at some point and then collapse. The universe is then CLOSED. This outcome is known as the Big Crunch.
  3. 3 If the actual density is less than the critical density, there is not enough mass to stop the expansion and the universe will continue to expand forever. The universe is OPEN.
  4. 4 Determining the actual density is difficult because there seems to be dark matter which we cannot yet detect directly but which can be inferred by the gravitational effects it has. e.g the rotation of galaxies is not consistent with observable mass but with increased mass that may be explained by the presence of dark matter.

  • Marked by Teachers essays 2
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  1. Peer reviewed

    What affects the voltage output of a solar panel?

    3 star(s)

    measure the diameter of the light bulb and hence calculate the distance between the point source to the solar cell Wires Used to connect the ray box to the power pack and the voltmeter to the solar cell Ruler Used to measure the distance between the point source and the solar cell A ray box is chosen over a light bulb as the light bulb will emit light out of all directions, while the ray box's light can be controlled to be emitted out through one direction, to the solar cell.

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  2. Dark Matter

    He also moved the planets off the center. Although this was wrong, it was helpful in predicting the position of the planets. Copernicus and his Explanation Nicolaus Copernicus was a Polish astronomer, and his explanation about how the solar system moves around the sun became the groundwork of modern astronomy. Furthermore, he proposed that the sun is the center of the universe. He said that if one assumed that the sun is the center of the universe, it would be simpler to describe the positions of the other planets and their movements, too.

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  3. Study the interference of light using Helium - Neon Diode Laser.

    the sources A and B are assumed to have the same wavelength and to be always in phase with each other. iii) resultant fig. 2 Figure 2(i) and (ii) illustrate the vibrations at X due to A and B, which have the same amplitude. The resultant vibration at X is obtained by adding the two curves, and has an amplitude double that of either curve, Figure 2 (iii). Now the energy of a vibrating source is proportional to the square of its amplitude . Consequently the light energy at X is four times that due to A or B alone.

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  4. Earthquake Simulation Program.

    Despite the small amount of movement of these plates, about 2-12 centimetres per year, the results are devastating. There are three directions that the rocks can move when they fracture: apart, together or past each other (shearing). Although there are a few exceptions, most earthquakes occur along the fault line of the two different sections of rocks, or. Due to continental drift, which plumes of rising, magma from can cause as far down as outer core/mantle boundary, this has resulted in the globe being broken up and separated into different plates that literally float on molten rock beneath.

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  5. Determine the value of 'g', where 'g' is the acceleration due to gravity.

    The gradient of the graph above determines the value on the spring constant 'k'. This value can be used in the equation of the simple harmonic motion for mass spring system as show below:- As we know that the mass spring system also obeys Hooke's law and therefore a force extension graph can be drawn to determine the value of 'k' for that particular spring being used in the experiment. I will use Hooke's law to determine the amount of load the spring can hold without deforming. If the spring does not return to its original shape then it is gone past it's elastic limit and is permanently deformed.

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  6. An experiment to investigate and determine how rubber behaves when tension forces are applied to it.

    the tension for when all tensions applied up to a certain stage and when the sample of material starts behaving in a more complex. Also some materials behave in ways that their extension is not proportional o the tension. I wish to see whether extension will have an effect on the proportionality on the tension and extension. Hooke's Law states that, "for relatively small deformations of an object, the displacement or size of the deformation is directly proportional to the deforming force or load.

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  7. What factors affect the period of a Baby Bouncer?

    The spring used was composed of ductile material (a material which can be stretched). The likely impact of increasing the load on the period of oscillation is that the oscillation period will increase in duration. * The material which the spring support is composed of: Usually spring supports are made out of metal or rubber. There is an increasing trend, for safety reasons, for the spring support to be made out of rubber. Employing different materials in the construction of the spring support would have a direct effect on the duration period of the oscillation, for example rubber, has a Young Modulus 0.01 GPa, Lead 18 GPa, Aluminium 70 GPa, Brass 90 - 110 GPa, Copper 130 GPa and steel 210 GPa.

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  8. Damping of an mechanic oscillator.

    I noticed a small sound for this experiment too. 3. Metre ruler I forced a 100.0cm ruler to oscillate by placing one of its ends on edge of lab desk. I pushed the other end verticaly downwards and released it. Here again the displacement decreased but particularly in a faster way and got back to its original position after a few seconds. The sound is sharper this time. Interpretation All of this examples show the same pattern of movement. The mass of pendulum speeds up from 0 (accelerates)

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  9. Stretching Springs/Hookes Law.

    This graph shows the increase in length of an elastic wire as the stretching force on it increases. Over the straight-line part of the graph there is a 10-mm increase in length for every extra Newton (N) of applied force. The change in length (strain) is proportional to the force (stress), a relationship called Hooke's law. The wire begins to stretch disproportionately beyond an applied force of 8 N, which is the wire's elastic limit. When this force is removed, although the wire will decrease in length somewhat, it will not go back to its original length. What happens to a spring when forces are added to it?

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  10. The aim of this investigation is to examine the effect on the spring constant placing 2 identical springs in parallel and series combination has and how the resultant spring constants of the parallel and series spring sets compare.

    As the magnitude of extension of the string approaches this elastic limit, the extension will gradually cease to obey Hooke's law. At this elastic limit, several changes in the composition of the spring can be observed. Whereas any stretching of a material that occurs below up until this limit is referred to as elastic deformation, stretching the material beyond this limit will result in permanent deformation of the material. Stretching that occurs beyond the elastic limit is referred to as plastic deformation.

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  11. I am doing an investigation in to how much a metre rule bends when one end is clamped to a table and a varied load is attached to the other end that hangs off the table, thus bending the rule.

    If the rule did snap, we could say that it had gone passed the elastic limit, which means that if something is bent beyond this point, in the case of the metre rule, it would snap and not be able to return to its original shape. Hooke's law can only be applied up to the limit of proportionality as after this, permanent damage is done to the metre rule. It no longer obeys Hooke's Law as equal increases in stretching force produce larger increases in extension than expected.

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  12. The Stiffness Of Springs

    However, if I do not exceed the elastic limit the formula F = kx will be applicable. I predict that a system of springs in series will have a different spring constant to a system of springs in parallel. I can use F = kx to show the different spring constants of spring systems in parallel and series. Then I can examine these results to show a relationship between them. To achieve this I must plan an experiment that shows the stiffness of different numbers of springs in series and I parallel. To find the spring constant of a spring I can place different masses onto a spring and measure the length of the extension of the spring.

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  13. An investigation into the stretching of materials

    Variables There are many things I could change to alter the outcome of my experiment. A list of variables I could change which may affect the results of my experiment are; � Length of the elastic band, � Width of the band, � Elasticity of band, � Previous stress and strain the band has undergone, � Weight of band, * Weight added to band, � Colour of band, � Temperature of band and room at time of experiment. I have deemed these last two factors insignificant as I feel they will not have an actual effect on the outcome of my experiment.

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  14. An Experiment To Examine the Effect of Springs In Parallel

    apart so less extension. Less force acts on each molecule. In series 1 spring In parallel '2 springs' If there are double the amount of springs in parallel then I predict that the extension will be half. I predict that the extension is inversely proportional to the number of springs. If I applied 2N to one spring and the extension was 5cm then if I added on another spring (in parallel), I would say the extension of the springs would be 2.5cm.

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  15. Waves and Cosmology - AQA GCE Physics Revision Notes

    Accelerating electron radiates energy and as its energy is lost; the electron will spiral towards the nucleus (due to electrostatic attraction) and collide into the nucleus, as it doesn?t have enough energy to remain in orbit. So it is suggested that electrons can only have certain discrete values/ quantized energies so there is a stationary wave with whole number of loops in the orbit. When n=1, there?s one loop (half a wavelength) When n=2, there?d be two loops (one whole wavelength) Fundamental particles * The standard model suggests that there are 2 types of fundamental particles ? leptons and quarks.

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  16. I intend to investigate whether any correlation exists between the wavelength of light exerted upon a small solar cell impacts its rate of increase to response time

    meaning that the risk of shock is extremely low. Care should still be taken as the variable power supply I am using can ramp up to 40v and 5 amps. As a result, I will limit the output of the power supply by leaving the ?High-Low? switch on the latter setting; effectively limiting the power supply to 15 volts and low amperage. The switch will be taped over to avoid accidental changes. The wavelength of the LED?s I am using poses no risk at all. They all form part of the visible spectrum so do not carry enough energy to ionise any bodily cells.

    • Word count: 4341

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