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G485
| Question | Answer |
|---|---|
| Define Electric field strength | The electric Field strength at a point is the force per unit charge exerted on a positive charge placed at that point |
| State Coulombs law (From centre to centre) | Any two point charges exert an electrical force on each other that is proportional to the product of their charges and inversely proportional to the square of the distance between them |
| Equation of coulombs law | F=Qq/4piEor^2 =kQq/r^2 (less precise) If F is negative - the force is an attraction |
| A point charge Q gives rise to a radial field. Electrical field strength = | Q/4piEor^2 |
| Horizontal velocity of electron in electric field | Unaffected because its perpendicular to the force (Fcos90=0) However it may begin to accelerate down. The force of gravity is negligable |
| properties of x rays | Short Wavelength high frequencies produced by high velocity electrons rapidly deccelerating |
| Intensity= | P/A or (E/T)/A |
| Compton scattering | An x ray photon loses only a fraction of its energies to an atomic electron in the absorbing material. The interaction between photon and electron is inelastic |
| Pair production | High x ray photon passing through electric field of a nucleus produces a electron-positron pair. |
| PhotoEE | Electron absobs low energy x ray with enough energy to escape the atom |
| Fleming left hand | Thumb - direction of motion First finger- Direction ofexternal magnetic field Second finger - Direction of conventional current |
| Define tesla | The magnetic flux density if 1T when a wire carrying a current of 1A placed at right angles to the magnetic field experiences a force of 1N per metre of its lenght |
| Define the Weber | = to 1 Tesla metre squared For magnetic flux linkage |
| The magnetic flux through Area A is defined as | 0/=BA Where B is the component of magnetic flux density perpindicular to the area |
| The magnitude of induced Emf (Faradays law) | Is proportional/equal to the rate of change of magnetic fluz linkage |
| Magnetic flux linkage | Defined as the product of number of turns and magnetic flux |
| Lenz's law | Any induced current or EMF willl be established in a direction so as to produce effects which oppose the change that is producing it |
| Capacitance define | The capacitance of a capacitor is the charge stored per unit potential difference across it. |
| QV graph | Area = work done = 1/2 QV = 1/2 CV^2 =1/2 *(Q^2/2) |
| Define the time constant (Capacitors) | The time constant is the time taken for the curretnt, charge stored, or pd, to fall 1/e (Apprx 37%) of its initial value |
| Define Isotopes | Isotopes are nuclei of the same element with a different number of neutrons but the same number of protons, |
| What are hadrons on Leoptons | Hadrons - consist of quarks (Up down strange) protons and neutrons, affected by the strong nuclear force Leptons - Sich as electrons - unaffected |
| The nucleon number is... | The number of protons and neutrons in the nucleus |
| What is conserved in hadron collisions | Charge, baryon number, strnageness, bottomness, topness, charm |
| Differnece between fission and fusion | Fission is the separation of a neleii, fusion is the joining of nuclei |
| Define the mass defect | The mass defect of a nucleus is equal to the difference between the total mass of the individual seperate nucleons, and the mass of the nucleus |
| What is the min energy needed to pull apart a nucleus. | The min energy needed to pull a nucleus APART into its seperate nucleons is known as the binding energy of the nucleus. |
| Define the decay constant | The probability that an individual nucleus will decay per unit time is called the decay constant |
| Define activity of a source | The activity of a radioactive sample is the rate at which nuclei decay or disintegrate |
| Define the half life of an element | The half life t1/2 of a radioisotipe is the mean time taken for half of the active nuclei in a sample to decay |
| Beta minus decay | Electron emmitted aswell as Anto neutrneo, down quark becomes up quark |
| Beta plus | Positron and neutreno, up quark becomnes down |
| uds, charge and baryon number and strnageness | Charge; +2/3, -1/3, -1/3 Naryon all 1/3 Strangeness 0,0,-1 |
| Define intensity | Power per unit corss sectional area |
| MRI | Spinning processing protons forced to resonate using RF pulses. When absorbed, using resonance, flip into high energy. protons relacx and emit RF, obtain diagnositc information by looking at relaxtion times, cancerous tissues have lower relax tinme |
| Advantages of MRI | Does not use harmful ionising radiation No moving mechanisms Patient feels nothing, no side effetcs Better soft tissue contrast then CAT Can be made 3D |
| Why can it MRI be dangerous | Metallic objects in human become heated, pacemakers can be effetced. |
| The acoustic independce changes | The fraction of the incident intensity of ultrasound that is reflected at the boundary. Z=pc (density, epeed of sound) |
| Formation of stars | Gas clouds, Where material is dence, gravity pulls material inwards, becoming dencer. "Collaps" gas heats up (As gpe -- Ke) Particles collide, share energy and heat up Temps reach enough to fuse - Hydrogen burning (to helium) Radiation pressure andG= |
| Ageing sttars <3 solar masses | Temperature and prssure in starts increases, more complex fusion, as fusion slows, star collapses under gravity prssure. Stuff fuses, increased power, expands dueto radiation pressure. Then RED GIANT. Very high temps and fuse. Area surrounding core ejecte |
| Ageing starts Pt 2 | Area surrounding core ejected as planetary nebula. Remains is white dwahrf, cooling, very dense, no hydrogen fusing. Glows due to photons still leaking. Prevented from further collapse by Fermi pressure |
| More mssive stars | SUPER RED GIANT, then as white dwahrf its gravity still causes collapse. Neutrenos espcape, left with neutrons (Neutron star). Outershells collapse rebound on neutron core, shock wave, explodes as supernove. Light-neutron star, if not Black hole (G coll |
| 1 Au | The average distance from earth to sun ( 1.5 10^11) |
| 1ly | The distance travelled by light in a vacum in one year (9.5 10^10) |
| 1 arc second | There are 60 arc seconds in a minute of arc, and 60 arc minutes in a degree 1 arc second = 1/3600 degress |
| 1 pc | The parssec is defined as the distance that gives a paralax angle of 1 arc second 3.1 10^16) |
| Hubbles law | Speed of recession of galaxy proportional to distance of galaxy v=HoX 1/Ho = age of ubniverse |
| Olbers paradox | For an infinite, uniform and static universe, the night sky should be birhgt because light recieved from all directions from stars (Its not static or infinite) |
| How to improve contast in X ray imaging | A substance is swollowed (Barium) or have it injected to area of interest, Tissue becomes a better absorber and edges show up clearer Atoms have more electrons fro xrays to interact eith. |
| Why use a CAT scan How do they work | produce 3D images Distinguish between similar density tissue Patient lies in ring of detectors, with x ray tube rotating round. Send to computer |
| Hadrons Leptons | Prtons neutrons Electrons |
| Induced fission | Neuton collides with large unstable nucleus, becomes unstable and splits |
| Funciton of moderator in fission reacotr | To slow the fast neutrons, hence greater chnace they will undergo fission (neutron strikes uranium, becomnes unstable and splits), neutrons released |
| Define magnetic flux density | B = F/IL |
| Pizoelectric crystal | When a voltage is applied in one direction, it shrinks, reveresed, expands. contrasts and shrinks at same frequency, induces starain. Vibrating source of ultrasound waves . It then rrecieves relected waves |
| Echo sounding | Interested in the fraction of the incident intensity of ultrasound reflected at boundary, depends on acoustic independence. z=pc, determines boundary. oscilloscop, V against T (A scan)). |
| Doppler effect useful for... | Determining speed of bloos, varying wavelenghts and frequencies of reflected waves |
Created by:
Ben Bailey