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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
  • Peer Reviewed essays 20
  1. Marked by a teacher

    Wave Coursework

    3 star(s)

    This will also increase the reliabilty of my results. I will then be able to work out an average, removing any error results out of limit. Before taking any readings of the wave velocity I will measure the length and width of the tray and also see if the tray is flat on the bottom and along the sides. I will do this by placing 1cm depth of water into the tray, taking the measurements at either end and in the centre of the tray.

    • Word count: 1223
  2. Peer reviewed

    Annihilation Theory

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    Matter and antimatter is a collective term given to two identical particles that are of opposite charge. Therefore they are the same with the exception of charge. There opposite charges adhere to the Laws of Attraction, which state that two particles of opposing charge are attracted to each other. On their collision they, theoretically, annihilate each other resulting in a gamma ray (pure radiation). This can be shown by; e+ + e- � ? (A positron plus and electron results in a gamma ray) Equations like these show the fundamental properties of all interactions. Here, the resultant is a gamma ray, which indicates that (considering that gamma particles travel at the speed of light)

    • Word count: 1111
  3. Peer reviewed

    The Electro magnetic spectrum.

    3 star(s)

    Their wavelength is usually a couple of centimetres. Stars also give off microwaves. Microwaves cause water and fat molecules to vibrate, which makes the substances hot. Thus we can use microwaves to cook many types of food. Mobile phones use microwaves, as they can be generated by a small antenna, which means that the phone doesn't need to be very big. The drawback is that, being small, they can't put out much power, and they also need a line of sight to the transmitter.

    • Word count: 1860
  4. Peer reviewed

    Investigate the effect of mass on the extension of a spring.

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    * Boss Clamp Hypothesis Using scientific knowledge from that of Hooke's law, I am able to conduct a hypothesis. Hooke's law reveals that the extension is proportional to that of the load, and so if load increases, so does the extension and so stretching the distance. He discovered that extension is proportional to the downward force acting on the springs and so we can use this formula to predict the results. Extension= New length - Original Length Prediction: I predict that the greater the weight applied to the spring, the further the spring will stretch. This is because extension is proportional to load and so if load increases so does extension and so stretching distance To see if my prediction is correct I will experiment, and obtain results using Hookes Law.

    • Word count: 1225
  5. Peer reviewed

    The effects of the extension of a spring on the time it takes a weight to oscillate.

    3 star(s)

    So therefore: 1/2 mv2 = maX 1/2 mass x velocity2 = mass x acceleration x extension (distance) The velocity value is the velocity at the mid point which is where the mass final comes to rest after oscillating. The formula can be simplified to: v2 = 2aX Velocity is distance/time and acceleration is force/mass therefore with substituting the formula is: (distance/time)2 = 2 x (Force/Mass) x X Which is equal to: (time2 / distance2) = mass / 2 x force x X The values on the top half of the formula are the constants in this experiment.

    • Word count: 1518
  6. Peer reviewed

    A report concerning stars and constellations

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    Even the Bible makes reference to this famous group. God, while pointing out how all-powerful he was, is purported to have asked Job if he (Job) was able to "loose the bands of Orion" Leo (Lion) The first on the list of Heracles' labours was the task of killing the Nemean Lion, a giant beast that roamed the hills and the streets of the Peloponnesian villages, devouring whomever it met. The animal's skin was impervious to iron, bronze, and stone. Heracles' arrows harmlessly bounced off the lion; his sword bent in two; his wooden club smashed to pieces. So Heracles wrestled with the beast, finally choking it to death.

    • Word count: 1498
  7. Peer reviewed

    See how one factor affects the period of time a mass on the end of a spring takes to complete one whole oscillation.

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    I have chosen to make mass the variable, as this is the easiest variable to use in this experiment. Equipment Here is a diagram of the equipment I will use: Method This is how I will carry out the experiments: 1. Set up the equipment as shown in the diagram 2. Put the mass on the end of the spring (see below for range) 3. Measure the initial displacement (see below) 4. Time 10 oscillations, and divide this answer by 10.

    • Word count: 1520
  8. Peer reviewed

    Properties of Waves.

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    Reflection can be used to guide a laser past obstacles to a receiver. Shiny surfaces such as mirrors are smooth so reflect all light strongly as all the waves pass in one direction only. Rough surfaces look dull as they reflect light in many different directions causing it to scatter. This is called diffuse reflection. If light waves are reflected, the colour of the surface affects the colour of the reflected ray. Concave surfaces are used to focus waves at a point to increase their strength, for example satellites collect radio waves in a dish, then focus the waves on to a point.

    • Word count: 1031
  9. Peer reviewed

    Astronomy - the urge to explore space.

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    It was also found out that the building door and the main door were at an angle of 20�. Astonishingly, this is the exact angle that the same two stars of the constellation had on each other. Until the 11th century the truth about the stars was unknown and there were just a few theories of Ancient Greeks. In the 11th century an Arab astronomer presented the hypothesis of the stars being a lot bigger mass than they appear to the naked eye. This theory was a great new discovery for the astronomers from all over the world and it opened a new era for the astronomers of the future.

    • Word count: 1303

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