Monday, 28 March 2011
Wednesday, 16 March 2011
Monday, 7 March 2011
Astrophysics: The Future of the Universe
E4.8
There are three different, proposed futures to the universe; Open, Closed and Flat.
All of these different futures rely on the benchmark density called the critical density which defines how much density would be required in order to have a flat universe (non-expanding universe.)
(You don't have to state the density, but it is 4.5E-27 or 4.5E-26)
An Open Universe represents an ever-expanding universe, with less mass than the critical density so that the overall mass of the universe is less than the critical density and the universe's gravitational pull isn't strong enough to pull it back on itself, therefore it keeps expanding.
A Closed Universe represents a universe containing more mass than the critical density and thus it has a greater gravitational pull than the others which can pull the universe back to the starting position. This is called the 'big crunch.' It has been theorized that after this 'big crunch' occurs another 'big bang' will occur as all the mass has come together in one small area forming another singularity.
There are three different, proposed futures to the universe; Open, Closed and Flat.
All of these different futures rely on the benchmark density called the critical density which defines how much density would be required in order to have a flat universe (non-expanding universe.)
(You don't have to state the density, but it is 4.5E-27 or 4.5E-26)
This graph shows the different futures for the universe.
(Chris Hamper, Physics Higher Level Book.)An Open Universe represents an ever-expanding universe, with less mass than the critical density so that the overall mass of the universe is less than the critical density and the universe's gravitational pull isn't strong enough to pull it back on itself, therefore it keeps expanding.
A Closed Universe represents a universe containing more mass than the critical density and thus it has a greater gravitational pull than the others which can pull the universe back to the starting position. This is called the 'big crunch.' It has been theorized that after this 'big crunch' occurs another 'big bang' will occur as all the mass has come together in one small area forming another singularity.
Monday, 21 February 2011
Astro
E1.1
Outlining the structure of the solar system, these graphs represent the distance from the sun, plotted on the x-axis against the time taken for one orbit, on the y-axis. This represents the increase in orbital time for bodies that are further away from the sun.
The second graph supports Kepler's Third Law, using a squared value for the orbital time and cubed for the distance from the sun.
E1.2
A stellar cluster (a.k.a. globular cluster) are physically close to each other and this phenomena is linked to gravity. Constellations on the other hand do not necessarily have to have stars which are closer together, as they are merely patterns formed in the sky using stars to connect the dots. It is purely imagination based.
Asteroids are celestial bodies that orbit the sun, made of rock and metal, usually around the inner solar system. A comet also orbits in an elliptical pattern around the sun, however it is composed of rock and ice.
Meteorites are the remnants of those two which has reached the surface of Earth.
E1.3
Light year. The distance that light travels in one year 9.46E15
E1.4
Comparing the relative distances:
Visible Universe: 1.5E26
Local Group of Galaxies: 5E22
Our Galaxy: 1E21
Solar System: 1E13
During a twelve hour cycle above Bangkok, Orion will look like this:
Monday, 31 January 2011
13.2.3 - 13.2.4
13.2.3
The nucleus, as a quantum system contains discrete energy levels. Alpha particles have discrete energies along with the gamma ray spectra. Quantum energy being emitted from both are quantized and discrete, only having certain values, and showing that the nucleus itself has discrete nuclear energy levels.
13.2.4
The beta energy spectra is continuous and was not understood before the postulation of the neutrino. As scientists were investigating they discovered that the beta particles had three times less emissions than what was predicted, undermining the basic principles of physics (conservation of energy.) This led to the postulation of the Neutrino. A particle that was almost undetectable and that carried away the missing kinetic energy and momentum present in the reaction. It is neutral with a minute mass, travelling at the speed of light.
During positron decay a proton contained within the nucleus decays into both a neutron and a positron, which are then emitted. Due to neutrinos and anti-neutrinos, the beta emissions form a continuous spectra.
The nucleus, as a quantum system contains discrete energy levels. Alpha particles have discrete energies along with the gamma ray spectra. Quantum energy being emitted from both are quantized and discrete, only having certain values, and showing that the nucleus itself has discrete nuclear energy levels.
13.2.4
The beta energy spectra is continuous and was not understood before the postulation of the neutrino. As scientists were investigating they discovered that the beta particles had three times less emissions than what was predicted, undermining the basic principles of physics (conservation of energy.) This led to the postulation of the Neutrino. A particle that was almost undetectable and that carried away the missing kinetic energy and momentum present in the reaction. It is neutral with a minute mass, travelling at the speed of light.
During positron decay a proton contained within the nucleus decays into both a neutron and a positron, which are then emitted. Due to neutrinos and anti-neutrinos, the beta emissions form a continuous spectra.
Monday, 24 January 2011
Sunday, 9 January 2011
Induced Electro-Motive Force.
12.1.1:
Emf is the amount of mechanical energy converted into electrical energy per unit charge. The unit of an induced emf is the volt. This happens when the free charges moving in a magnetic field are contained within a conductor. This is affected by the rate of flux cutting (Also just v for the velocity the conductor moves through the field), B - field of flux density and L, the length of the conductor itself. The optimal angle for a conductor to flux cut is perpendicular to the magnetic field lines.
12.1.2:
FB= FE
FB= BeV
E = -dV/dx = V/L
FE = Ee = Ve/L
Ve/L = BeV
V=BLV
12.1.3:
Faraday's law shows that the induced emf is equal to the rate of change of flux. This is due to the fact that the different variables, flux density, speed of movement and length of the conductor change at the rate which the conductor cuts through the magnetic field lines. This applies to all examples of induced emfs.
12.1.4:
This happens mainly during AC power production, where the power is sent primarily to the coil causing a change in the magnetic field in the transformer. Transformer-induced emf is induced by a time-changing magnetic flux, namely a wire in a magnetic field that changes with time.
12.1.5:
Faraday's: Total flux linkage is given by NФ. The rule governing induced emf can be stated as the magnitude of an induced emf being proportional to the rate of change of flux linkage. emf = N(ΔФ/Δt)
Lenz's: The direction of an induced emf opposes the change which caused it. For example if a current was induced downwards the force would be upwards. The original motion would be opposed.
Questions:
39.
a)
Emf = BLV
50x10^-6 x 0.2 x 20
= 2x10^-4 v
b)
R = 2
I=V/R
=2x10^-4/2
=1x10^-4 a
c)
I^2R
=2x10^-8 w
d)
2x10^-8 w
e)
20 meters in one second.
f)
w=fxd
f = w/d
f=2x10^-8 / 20 = 1x10^-9 N
40.
a)
AxB
2x10^-4 x 100 x 10^-6
=2x10^-8
=50x2x10^-8
=1x10^-6
b)
Since flux changed density to 50 then flux enclosed is 0.5x10^-6
ΔB/Δt = 1.0 – 0.5 / 2
=0.25 MTm^-2s^-1
c)
Induced emf = rate of change of flux = 0.25 MV
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