definitions 4 Flashcards
Generator?
An electromagnetic machine that uses rotation, often produced by a turbine, to produce the flux changes needed to produce an emf.
Gluon?
The exchange particle that mediates the strong nuclear force.
Grain boundary?
The lines along which grains meet in a crystalline structure.
Gravitational field?
The region surrounding a mass in which another mass would experience a force.
Gravitational field strength?
The magnitude and direction of the force on a mass of one kilogram at a given point in a gravitational field. Symbol g, units NKg^-1
Gravitational potential?
The gravitational energy per kilo of a material at a position, being the work done to move 1Kg from infinity to the place in question, JKg^-1.
Gravitational potential energy, Egrav?
Potential energy of a mass due to its position in a gravitational field. GPE diff between to places in a uniform field is mgh, where h is the vertical separation between 2 points.
Hadron?
A particle composed of 2 or 3 quarks. Protons and neutrons are hadrons.
Half-life?
The time taken for the number of radioactive isotopes in a radioactive source to half from its original value. Alternatively it is the time taken for the activity of a radioactive source to half from its original value. Symbol is T 1/2.
Half-thickness
The thickness of an absorber needed to half the number of photons that can pass through it on average.
Hard?
A material whose surface is hard to scratch or dent. For example, ceramics.
Heavy damping?
Reduction of simple harmonic motion in which the oscillator returns to the equilibrium position much more slowly than a lightly damped or critically damped oscillator.
Hertzprung-Russel diagram?
A logarithmic plot of luminosity of stars against their surface temperature.
Hubble’s law?
In a plot of the speed of recession of galaxies against their distance, distant galaxies seem to be moving away from us, and their speed is proportional to their distance.
Hydrogen bond?
A weak bond between molecules bearing separated charges. e.g. the negative part of one water molecule and the positive part of a neighbouring one.
Ideal gas?
A gas in which the molecules don’t interact at all and are so small that they occupy negligible volume.
Impulse?
The product FΔt summed over the whole action of a force on an object resulting in a momentum change. Δp= impulse.
In parallel?
Components of an electrical circuit joined alongside each other which share a current and have the same pd.
In series?
Components in an electrical circuit joined end to end which share the pd and have the same current.
Induction?
The creation of an emf across a circuit when the magnetic flux in the circuit is changed.
Inertia?
The tendency for a stationary object to stay stationary or a moving object to continue with the same momentum.
Input voltage,Vin?
The pd applied to a sensor circuit (frequently a potential divider).
Insulator (electrical)
A material that conducts electricity poorly on account of having very few charges which are free to move.
Intensity?
Intensity of a wave is the energy per unit of time carried by the wave and incident normally per unit area of surface.
Interference?
From the superposition of a waves on top of one another. When waves overlap the resultant displacement will be equal to the sum of the displacements at that point and at that instance. Produced if waves from two coherent sources overlap or if waves from a single source are divided and then reunited.
Internal energy?
The energy, U, stored within a system allowing it to do work or transfer energy thermally.
Internal resistance?
Resistance within a source of emf causing a drop of terminal pd when a current is drawn from the source.
Ionic bond?
A strong bond between ions due to electrostatic attraction.
Ionisation?
Removal or addition of an electron to an uncharged atom or molecule resulting in the formation of an ion.
ionisation energy?
The energy that must be supplied to a neutral atom or molecule to ionise it.
Isotope?
Forms of the same chemical element that have the same proton number but a different neutron number.
Iteration?
A repeat of a mathematical operation, often used in modelling-for example iterative models are used to model exponential decay.
Iterative model?
A mathematical treatment, often using a computer, whereby small step wise changes to variables such as displacement and velocity are made in regular time intervals, Δt with the assumption that the variables change only at the end of each time interval.
