665014
Description
Flashcards by nicola.bowen, updated more than 1 year ago
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Created by nicola.bowen
over 10 years ago
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| Question | Answer |
| Capacitor | A pair of conducting plates separated by an insulator. If a p.d. is placed across the plates they acquire equal and opposite charges. |
| Capacitance, C, of a capacitor | (Charge on either plate)/(p.d. between plates) units F(farad) |
| Dielectric | Insulator between plates of a capacitor, also serving to make the capacitance larger than if there were just empty space |
| Magnetic field strength B | A vector quantity.. Direction is that in which the North pole of a freely pivoted magnet points. Magnitude defined by F=BIL where F is the force on a length L of wire carrying a current I placed perpendicular to the direction of the field. Units T(tesla) |
| Hall voltage | When a magnetic field B is applied to a conductor carrying a current I at right angles to the field direction a so called hall voltage appears across the specimen at right angles to the B and I directions |
| Ampere | The ampere is that current which, when flowing through two infinite parallel wires, one metre apart in vacuum, produces a force between the wires of exactly 2x10^(-7) N per methre of length. Units A |
| Magnetic flux | If a single turn coil of wire encloses an area A and a magnetic field B makes an angle o with the normal to the plane of the coil, the magnetic flux through the coil is given by ABcos(o). Unit Wb(weber) |
| Flux linkage | If the above coil consists of N turns the flux linkage is given by N*magnetic flux. Unit Wb or Wbturn |
| Faraday's Law | When the flux linking an electrical circuit is changing an emf is induced in the circuit of magnitude equal to the rate of change of flux linkage. |
| Lenz's Law | The direction of any current resulting from an induced emf is such as to oppose the change in flux linkage that is causing the current. |
| Root mean square (RMS) value | If an alternating voltage is read at regular intervals throughout a cycle, giving the values V1,V2..VN the rms p.d. is defined as Vrms =root(1/n V1^2 + V2^2....+Vn^2) |
| Alpha radiation | Fast moving particles, helium nuclei, ejected from certain radioactive nuclei |
| Beta radiation | Electrons with speeds just less than the speed of light, ejected from certain radioactive nuclei |
| Gamma radiation | Photons of high energy (high frequency, short wavelength) ejected from radioactive nuclei |
| A/Z X notation | X is the chemical symbol of the element, A is the mass number and Z the atomic number |
| Half life of a nuclide | The time taken for the number of radioactive nuclei N to reduce to one half of the initial value. Unit s |
| Activity A | The rate of decay (number of disintegrations per second) of a sample of radioactive nuclei. Unit Becquerel (Bq) |
| Decay constant | The constant which appears in the exponential decay law N=Noe^(-lamdat) and determines the rate of decay (the greater lamda the more rapid the rate of decay) lamda is related to half-life by (ln2)/half life =lamda. Units /s |
| Radio-isotopes | Isotopes of an element have the same atomic number Z but a different mass number A; radio isotopes are simply isotopes which are radioactive. |
| Unified atomic mass unit u | The unified atomic mass unit is defined as exactly 1/12 of the mass of one atom of carbon -12. Thus one atom of carbon 12 has a mass of exactly 12u |
| Electron-volt | This is the energy transferred when an electron moves between two points with a potential difference of 1 volt between them. 1eV = 1.6*10^(-19)J. So for an electron being accelerated it is the KE acquired when accelerated though a p.d of 1V |
| Binding energy of a nucleus | The energy that has to be supplied in order to dissociate a nucleus into its constituent nucleons. (Not energy the nucleus possesses) unit J |
| Conservation of mass-energy | Energy cannot be created or destroyed, only transferred from one form to another. We can measure the energy in a body by multiplying its mass by c^2 |
| Nuclear Fission | Certain nuclei of large mass number can absorb a neutron and will then split into two smaller, beta radioactive, nuclei. Two or more neutrons are also released. The fragments have larger kinetic energies. This is called nuclear fission. |
| Chain reaction | A chain reaction is repeated events of nuclear fission in a sample of fissile material, initiated by neutrons released in previous fissions |
| X-rays | High energy e-m radiation with photon energies between 100eV and 100keV |
| A-scan | Scan in which the strength of reflections of an ultrasound pulse from interfaces in the body is shown by the amplitude of a trace. |
| B-scan | Scan in which the strength of reflection of an ultrasound pulse from interfaces in the body is shown by the brightness of a trace. An array of transducers can produce a 2D image. |
| Acoustic impedance | The property of materials which determines the fraction reflected. |
| Coupling medium | Gel or oil used to exclude air between the skin and the ultrasound transducer. It reduces the mismatch in Z and enables more ultrasound to enter the body instead of being reflected off the skin. |
| Precession | The spin direction of protons rotate around the magnetic field direction, like a child's top. |
| Relaxation time | The time taken for the protons to flip back to their lower energy state. |
| ECG | Produced due to the nervous impulses associated with the heart beat being detected outside the body, a voltage time chart. |
| Atrium/atria | The top chambers of the heart |
| Ventricle | The lower chambers of the heart |
| Sino-atrial node | Sends a signal which triggers the muscles of the heart to contract. Located at the top right of the heart. |
| Surface potential | Voltage measured on the skin due to nerve signal within the body. |
| Contraction | Shortening of muscles in response to nerve stimulus. |
| Absorbed dose | The radiation energy absorbed per kilogram of tissue. |
| Dose equivalent | Q * absorbed dose in which Q is a factor which depends on the type of radiation and takes account of the biological effect of the radiation. |
| Quality factor (Q) | 20 for alpha radiation and 1 for beta and gamma in equation: dose equivalent = Q *absorbed dose |
| Radioactive tracer | Chemical compounds with an atom replaced by a radioactive isotope - used to track the uptake of the compound by the body. |
| Tracer | Used to investigate function of particular organs |
| Electron capture | A method of decay where an element reacts with an electron to produce an isotope in an excited state which gives off gamma radiation. |
| Collimator | Device for producing a parallel beam |
| Scintillation crystal | Flashes of light are given out by certain crystals when high energy particles strike them. |
| Photomultiplier | An arrangement of electrodes with different voltages applied to them, so that electrons emitted from one electrode by the photoelectric effect are effectively multiplied in number to make a much larger current. |
| Positron | The antiparticle of an electron, the particle emitted in B+ decay. |
| Annihilation | When a particle and its antiparticle meet at low speed their mass energies are converted into photons |
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