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# Physics G485

TermDefinition
Define Electric Field Strength, E Electric field strength at a point in space is the force per unit (positive) charge. E=F/Q. E=V/d
Define Magnetic Flux Density, B F=BILsinӨ, where F is the force on a wire of length L carrying a current I at an angle Ө to the field. F=BQv(sinӨ). F=BIL(sinӨ)
Define Tesla, T One Tesla is the uniform magnetic flux density when a wire of length 1m and carrying a current of 1A at a right angle to the field experiences a force of 1N.
Define Magnetic flux, Φ Φ = BAcosӨ where B is the magnetic flux density, A is the area the flux passes through at right angles, and Ө is the angle between the plane of the area and the projection surface.
Define The Weber, Wb The magnetic flux when a magnetic field of flux density 1T passes at right angles through an area of 1m2 1Wb = 1Tm-2
Define Magnetic Flux Linkage The magnetic flux through the coil x the number of turns on the coil. Flux linkage = N Φ
Define Capacitance, C Capacitance = charge stored per unit potential difference. Ratio of charge to potential for a conductor (C=Q/V) Energy stored by a capacitor(W) = 1/2QV = 1/2CV2 = Q2/2C
Define The Farad, F One coulomb per volt. 1F = 1CV-1
Define The Time Constant of a Circuit Time for the charge to have decreased to of its initial charge. Time constant = CR
Define Proton Number, Z The number of protons found in the nucleus of an atom
Define Nucleon Number, A The mass number, the sum of the number of neutrons and protons in an atomic nucleus
Define Isotopes Define Isotopes Different forms of the same element (two nuclides) which have the same number of protons but different numbers of neutrons in their nuclei
Define Activity (Radioactivity) Spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay
Define The Decay Constant, λ The probability of decay of a nucleus per unit time Reciprocal of decay time. A = λN
Define Half Life (of a radioactive nuclide) Time taken for the number of un-decayed nuclei to be reduced to half its original number
Define Binding Energy The energy required to separate all the nucleons of a nucleus. The energy equivalent of the mass defect of a nucleus.
Define Binding Energy Per Nucleon The total minimum energy needed to completely separate all the nucleons in a nucleus, divided by the number of nucleons in the nucleus
Define Intensity Power per unit cross sectional area(W/m²)
Define The Distance Measured In Astronomical Units (AU) The mean distance from the centre of the Earth to the centre of the Sun.
Define The Distance Measured In Parsecs (pc) Distance from a base length of 1 AU that subtends an angle of 1 (arc) second
Define The Distance Measured In Light-Years (ly) The distance travelled by light in one year
Define Critical Density The density above which it is believed the expansion of the universe will slow down and reverse
State and use Faradays Law of electromagnetic induction Induced e.m.f is proportional to the rate of change of (magnetic) flux
State and use Lenz’s law Direction of any induced current is in a direction that opposes the flux change that causes it. Lenz + Faraday: E= - Δ Φ / t
State and use the equation for the total capacitance of two or more capacitors in parallel C = C1 + C2 + C3...
State and use the equation for the total capacitance of two or more capacitors in series 1/Ct = 1/C1 + 1/C2 + 1/C3...
State the quantities conserved in a nuclear decay The charge, the total number of neutrons and protons, total energy, the total momentum of the system and the total lepton number.
Beta minus decay Neutron -> proton + electron + anti-neutrino
Beta plus decay Proton -> neutron + positron + neutrino
State that electrons and neutrinos are members of a group of particles known as..? Leptons
State the approximate magnitudes in meters of the parsec 3.1 x 10^16 metres.
State the approximate value in meters of the light-year 10 x 10^15 metres.
State Olbers’ paradox With an infinite number of stars in an infinite universe, it does not matter which direction you look in - you will always see a star along the line of sight. therefore, the night will be as bright as the day sky.
State and interpret Hubble’s law The speed of recession of a galaxy is proportional to its distance from the Earth
State the cosmological principle Universe is isotropic /same in all directions Homogeneous / evenly distributed
Explain that the area under a potential difference against charge graph is equal to the..? energy stored by a capacitor. W=1/2QV = 1/2CV2 = Q2/2C
Explain exponential decays as having a constant ratio property
Explain how soft tissues like the intestines can be images using barium meal The patient swallows a liquid rich in barium as it will readily absorb X-rays. The barium meal coats the wall of the tract enabling its outline to be seen in X-rays.
Explain what is meant by the Doppler effect Doppler effect is a change in frequency and wavelength of a wave. It is caused by the change in distance between the thing creating the wave and whatever is measuring, seeing or hearing the wave.
Explain qualitatively how the Doppler effect can be used to determine the speed of blood Doppler effect uses ultrasound waves. Sound waves are reflected by the moving blood cells. Change in frequency/wavelength enables the speed of blood flow or rate of flow of blood to be found
Explain how ultrasound transducers emit and receive high frequency sound In this case electrical energy is converted into ultrasound energy by means of a piezo-electric crystal such as a quartz
Explain that the universe can be ‘open’, ‘flat’ or ‘closed’, depending on its density Open: Universe expands for all time Flat: expands to a limit (but never reaches it) Closed: Universe contracts / collapses back
Describe the difference between A-scan and B-scan A-scan in one direction only / range or distance or depth finding B-scan uses a number of sensors or a sensor in different positions / angles (to build up a 2D/3D image)
Describe the importance of impedance matching The greater the mismatch, the more ultrasound is reflected
Describe the solar system in terms of the Sun, planets, planetary satellites and comets Solar system contains 9 well known planets and their satellites; it also contains a number of small or dwarf planets. These planets all orbit the sun. Comets have an elliptical orbit. They return regularly often close enough to the earth to be visible.
Describe the formation of a star, such as our Sun, from interstellar dust and gas. -Hydrogen protons drawn together by gravitational forces (Gravitational collapse) -GPE decrease, KE increase. -Causes temp increase till fusion of protons occurs. -stable when thermal pressure = gravitational pressure
Describe the sun's probable evolution into a red giant and white dwarf -Hydrogen runs out, core shrinks. -Pressure builds, causes core to expand. -Red giant formed. Eventually becomes white dwarf, which is: ->Very dense, high surface temp, no fusion takes place. ->Collapse prevented by Fermi pressure /mass < 1.4 Solar ma
Describe how a star much more massive than our Sun will evolve into a super red giant and then either a neutron star or a black hole -Hydrogen runs out, core shrinks, red giant. -Core of the star collapses, supernova formed -Depending on initial mass, supernova results in neutron star or black hole.
Describe and interpret Hubble's red shift observations Wavelength of identifiable spectral lines did not correspond to wavelengths measured on earth -Column of light shifted to red end of spectrum. -Interpreted as continuous expansion of the universe.
Describe and explain the significance of the 3K microwave background radiation Leftover radiation (strecthed over time) from events in the big bang.
Describe qualitatively the evolution of the universe 10-43s after the big bang until present -Very hot, all forces were unified. -Expansion led to cooling -Quarks / lepton soup -More matter than anti-matter -Quarks combine to form hadrons. -4:1 protons -Gravitational force responsible for forming stars / galaxies -Temp becomes 2.7K
Created by: Danletch

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