Definitions U1 Flashcards
Hookes law
The extension of a spring is directly proportional to the force acting on it up to the limit of proportionality
Stress
Applied force per unit area of cross section
Ultimate tensile stress
Max stretching force per unit area without material breaking
Strain
Ratio of change in length to original length of specimen
Young’s modulus
Measure of stiffness of material, got by ratio of stress divided by strain
Microscopic
Small scale
Macroscopic
Large scale
Isothermal
Constant T
Boyles law
For fixed mass of gas at constant T the V is inversely proportional to the p
Charles law
For fixed mass of gas at constant pressure V is directly proportional to the T in Kelvin
Pressure law
For fixed mass of gas at cons V the p is directly proportional to the T in kelvin
Mole
Amount of substance which has as many particles as there are in 12g of C-12
Specific heat capacity
Thermal energy required to raise the T of a body of mass 1kg by 1K
STP standard temperature and pressure
0 degrees Celsius
1x10 ^5 Pa
Centripetal
Centre seeking
Angular velocity
Rate of change of angular displacement
Simple harmonic motion
Acc is directly proportional to the displacement
Acts towards fixed position
Damping
Resistive force which opposes motion and so causes the amplitude to decrease
Resonance
External force drives another to oscillate with greater amplitude at specific frequencies
Free vibrations
No energy transferred to or from system, amplitude is fixed
Forced vibrations
Forced to oscillate at frequency of external oscillator
Isotope
Atoms of element with same number of protons but different number of neutrons
Ionisation
Converts atom, molecule or substance into ion(s) by removing 1 or more electrons
Background radiation
Ionising radiation present in the environment
Exponential decay
Decay that falls by fixed fraction per unit time
Activity
Number of degradations per second in sample, measured in Bq
Decay constant
The fraction of total number of nuclei present to decay per unit time
Half life
Time for number of radioactive nuclei to decay to half its original value
Unified atomic mass
1/12 mass of one atom of C-12
u = 1.66x10^-27
Electron volt
Unit of energy equal to work done by electron accelerating it through a pd of 1V
Binding energy
Energy required to split up a nucleus into its nucleon parts
Binding energy per nucleon
Av energy required to remove a single nucleon from its nucleus
Mass defect
Difference between mass of separated nucleus and combined mass of nucleus
Nuclear fission
Splitting of large nucleus into lighter nuclei with release of energy
Nuclear fusion
Joining of 2 light nuclei to form one heavier more stable nucleus which releases energy
Conditions required for fusion
Nuclei must be confined within a finite Volume at sufficient temperature to increase chances of collision with enough energy to overcome the electrostatic repulsion
D-T reaction
2,1 H + 3,1 H -> 4,2 He + 1,0 n + 17.6MeV
Internal energy
Sum of ke and pe in a molecule
Kinetic theory ideal gas assumptions
F e v V t
No intermolecular forces
V and t are negligible
v is constant
Energy is conserved as collisions are elastic
Critical size, what should be greater than the critical size? What should be less than the critical size?
Minimum size of nuclear fuel to sustain a chain reaction
Total amount of fuel
Amount of fuel in each rod
Moderation
Slows fission neutrons (doesn’t absorb them) so that U-235 absorbs them
Control rods
Material
Inserted to control number of neutrons that are able to cause further fission
Boron/Cadmium
Cooling system (substance)
Water or CO2 is circulated around the fuel rods to cool them. Energy is passed to a heat exchanger where it is used to power a steam turbine
Reactor shielding (material)
Thick steel and several metres of concrete surround reactor, preventing harmful radiation from escaping
