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AS and A Level: Waves & Cosmology

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Redshift

  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.

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  1. An investigation into the effects of a force applied to a spring and the time for it to complete a set number of oscillations

    The temperature for this investigation will be room temperature, approximately 23?C. The same spring will be used. The same displacement for the spring will be used. The same spring will be used because of differences in the spring constant. The number of oscillations the spring hast to complete will always be 10. Scientific knowledge When using springs in an investigation, it helps to revise/research a law called Hooke's Law. This is a formula that states that the force acting on a spring and the spring extension have a constant relationship. Which can be expressed by the simple equation: F=KX Force=constant x extension Using this formula, we can find the constant of

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  2. Finding the Spring Constant (k) and Gravity (g) using Hooke’s Law and the Laws of Simple Harmonic Motion

    Clamp and Stand 2. 10gram weights 3. Ruler - accurate ? 0.5mm 4. Stopwatch - accurate ? 0.005 seconds 5. Digital scientific scales - accurate ? 0.005g 6. Spring 7. Marker 8. Safety Glasses 9. Gloves Procedure 1. Set up the equipment as below: 2. Safety - Put on safety glasses and gloves as the spring could snap as we put more weight onto it. 3. Place first weight on scales and record mass in the table under mass. (mass must be in kilograms. All results should be recorded to 3 d.p.) 4. Place mass on end of spring 5.

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  3. Stretching Rubber Bands

    Therefore the load it can take will be 0g. I also predict that each time the rubber band is stretched it will be slightly longer then it was previously. This is because rubber is a polymer, which has a very tangled structure. It looks like this: - Every time it is stretched the structure becomes less tangled, thus making it longer. For this reason, I believe for each set of results the extension will increase slightly. Apparatus * Clamp and stand * Rubber band * 1g weights and holder * G clamp * Meter ruler * Mirror * Pin Safety I will ensure that the following things happen, to ensure the experiment is safe: - * Safety glasses are worn while the rubber band is being stretched.

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  4. Investigation to find a value of g using the oscillations of a spiral spring.

    I took 7 results for both experiments. The preliminary tests, were to test the spring, and see how far it could stretch before exceeding its elastic limit. I loaded the spring up, with slotted masses. One at a time, until the spring broke. I measured the extension for each load, and plotted a graph from my results. I could see on my graph, that where the line was straight, the spring hadn't exceeded its elastic limit. Where the graph began to curve was where it had exceeded its limit.

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  5. To find out if the motion of an elastic band changes the tension, by the rate of its extension

    The elastic band will be catapulted off the end of another meter stick, in front of the ones that are taped to the wall. The band will be flung off the end of a meter stick, because the extension of the band can be measured easily using the units along the side of the meter rule. The height reached at each extension of the band will be recorded in a table of results along with a row of predicted heights at which the band may reach with each extension.

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  6. To find out if Hooke’s Law can be proved with a steal spring and to see what would happen if the spring is stretched beyond the elastic limit.

    To make the tests fair I will use the same spring and set of weights each time. Also I will add the weight proportionally in 1 Newton (10kg) each time. Therefore the change in weight will remain the same. My prediction is that Hooke's Law can be proved through a steel spring, as if the weight on the spring will increase so will the extension. The apparatus needed to do this experiment are a steel spring, a metre ruler, a clamp and weights. Hooke's Law found that extension is proportional to the downward force acting on the spring.

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  7. To find the separation of a pair of double slits using youngs experiment.

    * D)/y EQUIPMENT: * Monochromatic light (red laser) * Measuring tape * Double slit * Piece of paper * Pen PROCEDURE: 1. Set up the apparutus as per the diagram below: 2. Turn on the Monochromatic light and put the double slit in place so that an image similar to the one below is visible on the paper 3. Mark with a pencil the centre of 10 of the lines projected on the paper 4. Measure the distane,D between the laser and the paper, and record as 'D' 5.

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  8. Investigating factors which affect the period of an oscillating spring

    Fair test I will keep this experiment fair by using the same spring each time to ensure the constant "k" stays the same. I will be pulling the spring down by the same amount each time and I will be using the same ruler to take all measurements. Range and Repeats I will be taking 10 readings ranging from 100g to 1000g I intend to repeat the experiment twice carrying it out 3 times in all. This way I can obtain more accurate and reliable results.

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  9. What effects displacement of a ray of light?

    of the displacement 5 readings will be taken; this is because a large range of results is required to draw an accurate graph. A ruler will be used to measure the displacement and thickness and a protractor will be used to measure the angle. The experiment will be repeated twice to give a range of measurements The test will be kept fair by making sure that the controlled variables are kept the same throughout all the experiments. The main controlled variables are: Colour of light- white light must be used in every experiment as the colour of light may affect the displacement.

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  10. 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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  11. 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.

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  12. The physics of white dwarf stars.

    No longer having the gravitational pull of the sun, the earth and other planets would wonder the galaxy. The Pauli exclusion principle is defined by Dr. Steven S. Zumdahl, "In a given atom no two electrons can have the same set of four quantum numbers." Due to this principle, only two electrons can inhabit a single energy level. The electrons that share the same energy level have opposite intrinsic angular momentums which is more commonly known as "spin". To determine the direction of the spin the angular momentum vector is analyzed.

    • Word count: 948

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