Fields, Particles and Frontiers of Physics Flashcards
(135 cards)
Define capacitance
Charge stored per unit potential difference
What are the two assumptions of Olber’s paradox
- static/homogeneous
- infinite/infinite number of stars
Describe how the fate of the Universe depends on its average density. (3 marks)
- if average density of universe is less than critical then it will be too small to stop it expanding
- if the average density of the universe is greater than the critical value it will cause the contraction
- close to critical value and therefore expands at an ever decreasing rate asymptotic
Describe the evidence for the hot big bang model of the Universe
- galaxies moving apart
- if galaxies have always been moving apart at some stage they must have been closer together.
- evidence in red shift microwave
- further away the galaxy the faster the speed of recession
- the existence of a (2.7K) microwave
- there is more helium in the universe than expected.
Electric Field Strength (equation)
Voltage (p.d.)/ separation of plates
Define magnetic flux
a measure of the strength of the magnetic field
Explain why the magnitude of the magnetic flux through the coil varies as the coil rotates (generator)
The component of B perpendicular to the area changes.
Maximum when the field is perpendicular to B
Depends on cos(feta)
State Faraday’s Law of Electromagnetic Induction
The induced e.m.f is directly proportional to the rate of change of flux linkage.
(On a graph of MF against time) Describe and explain the variation with time of the induced e.m.f across the end of the coil.
- e.m.f. max when MF is zero…(give figure)
- e.m.f. zero when MF is a max…(give figure)
- e.m.f and MF have the same frequency
Explain why the activity of a radioactive material is a major factor when considering the safety precautions in the disposal of nuclear waste.
- material with small decay constant/ long half life activity will last for a long period period hence need long term disposal.
- material with large decay constant/ short half life have initial high activity hence precautions needed for initial period of disposal.
In beta-minus decay you also get an….
antineutrino
In beta-plus decay you also get a…
neutrino
Beta-plus decay in terms of quark model
uud -> udd
Beta-minus decay in terms of quark model
udd -> uud
Name the force responsible for beta decay
weak
Nuclear reaction: Explain how this reaction is able to produce energy
- binding energy of the products is greater than uranium
- energy available is the difference between the binding energies uranium and the sum of products
- E=mc^2
Nuclear Reaction: state what form the energy is released in such a reaction
KE
Explain why the neutron has no binding energy
the neutron is a single nucleon/ cannot be split further
(Two protons are accelerated at each other) The two protons fuse together. Explain how they are able to remain together.
Attractive strong force
(Proton accelerated towards other) Explain why the proton must have a very large velocity for the fusion to occur and the protons to remain together.
- as proton travels towards the stationary proton it experiences a repulsive force that slows it down
- therefore it needs a high velocity to get close to the proton.
Explain how image intensifiers are used to improve the quality of the X-ray image.
- Absorption of x-rays by photographic film.
- uses of fluorescent/scillinator
- photons release electrons
- no. of electrons increased/multiplied
Explain how contrast media are used to improve the quality of the X-ray image.
- different soft body tissue produce a little difference in contrast/attenuation
- high atomic number/ iodine or barium- gives greater contrast
- liquids injected or swallowed into soft tissue areas.
Collimator
gamma (ray photons) travel along the axis of lead
tubes or allows parallel gamma (ray photons travel to the
scintillator)
Electric Field Strength
force per unit charge