Combo Flashcards
Astronomical unit (AU)
The average distance between the Earth and the Sun.
Parsec (pc)
The distance that gives a parallax angle of 1 arc second
Light year (ly)
The distance light travels in a vacuum in 1 year
Olber’s paradox
For an infinite, uniform and static universe the night sky should be bright not dark because of light received in all directions from stars
Hubble’s Law
The recession speed of distant galaxies is directly proportional to their distance from the observer
Cosmological principle
The universe is homogenous, isotropic and the laws of Physics are the same at all points within it
Critical density
The density of the universe which would cause it to be flat – i.e. the expansion rate would tend towards zero in infinite time.
(Stellar) parallax
The apparent shifting in position of a star relative to the background of distant stars when observed from different positions in the Earth’s orbit round the Sun.
Capacitance
The stored charge in a capacitor per unit potential difference across the plates.
Farad
The capacitance of a capacitor which stored a charge of 1C when a voltage of 1V is across the plates.
Capacitors in series
Same as resistors in parallel
Capacitors in parallel
Same as resistors in series
Capacitors in parallel
Same as resistors in series
Capacitive time constant
The time taken for the current, charge and p.d. for a capacitor to fall to 1/e (37%) of its original value when discharging through a resistor.τ = RC
Proton number (or atomic number)
The number of protons in the nucleus of an atom
Neutron number
The number of neutrons in the nucleus of an atom
Nucleon number (or mass number)
The number of protons and neutrons in the nucleus of an atom
Plum Pudding model
A model of the atom in which negative charges are distributed throughout a sphere of positive charge
Isotope
An atom with the same number of protons in the nucleus but a different number of neutrons
Conservation of ___
The total ___ before a nuclear change will equal the total ___ after.
Quantities conserved in nuclear decay
Nucleon number, mass-energy, lepton number, baryon number, charge
Atomic mass unit
A 1/12th the mass of a C-12 nucleus
Thermal neutron
These are slow-moving neutrons
Control rods
Rods of a neutron-absorbing material used to reduce the rate of a nuclear chain reaction
Coolant
A substance used to transfer thermal energy from the core of a nuclear reactor
Induced nuclear fission
A fission reaction started when a neutron is absorbed by a nucleus
Mass defect
The difference between the total mass of the individual, separate nucleons and the mass of the nucleus
Moderator
A material used in a nuclear reactor to slow down fast-moving neutrons so that they have a greater change of interacting with the fissile nuclei
Activity
The rate of decay or disintegration of nuclei in a radioactive sample
Decay constant
The probability of a nucleus decaying per unit time
N as in A = λN
The number of undecayed nuclei in a sample
Half-life
The mean time taken for half the number of active nuclei in a radioactive sample to decay
Chain reaction
An exponential growth of a fission reaction caused by the increasing flux of neutrons causing fission
Spontaneous
Occurs without external influence
Random
Cannot be predicted
Binding energy
The minimum external energy required (per nucleon) to separate all the protons and neutrons in a nucleus
Binding energy per nucleon
The minimum external energy required (per nucleon) to separate all the protons and neutrons in a nucleus
Antimatter
Particles with the same mass but opposite charge and properties
Annihilation
When matter and antimatter collide to produce gamma ray photons only
Electro-magnetic intensity
Electromagnetic power per unit cross-sectional area
Photon
A quantum of electromagnetic energy
Electric field strength
The electric force per unit positive charge
Torque of a couple
One of the forces multiplied by perpendicular distance between the two forces
Coulomb’s Law
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.
Fleming’s left-hand rule
The rule used to predict the direction of the force experienced by a current-carrying conductor placed in an external magnetic field.
Solenoid
A long current-carrying coil used to generate a uniform magnetic field within its core
Magnetic flux density
The strength of a magnetic field, given by the magnetic flux lines per unit area perpendicular to the flux lines
Tesla
The strength of a magnetic field that will produce a force of 1N on a current of 1A in a wire of length 1m at right angles to a magnetic field.
Fleming’s right-hand rule
The rule used to predict the direction of the induced current on a moving conductor in an external magnetic field
Electromotive force
The energy transferred to electrical per unit charge
Magnetic flux
The product of magnetic flux density normal to a circuit and the cross-sectional area of the circuit.
Weber
The number of flux lines through a 1m2 area in a field of strength 1T.
Magnetic flux linkage
The product of the magnetic flux and the number of turns on a coil.
Faraday’s law
The induced emf in a circuit loop equals the rate of change of magnetic flux linkage.
Lenz’s law
The induced emf is in a direction that opposes the change producing it.
Thermal equilibrium
No net heat flow between objects
Pressure
Force per unit area
Internal energy
The sum of the random distribution of kinetic energy and potential energies associated with the molecules of a system.
Specific heat capacity
The energy required per unit mass of a substance to raise its temperature by 1 degree
Absolute zero
The temperature at which the internal energy of a system is a minimum
1 mole.
The amount of a substance such that there are 6.02x10^23 basic particles present.
Avagadro’s Constant (NA)
6.02x10^23 – the number of particles in a system when there is 1 mole present.
Specific Latent Heat (L)
The energy supplied to change phase of 1Kg of substance at constant temperature.
Latent heat of fusion
The energy absorbed by a substance to change its state from solid to liquid with no change in temperature
Latent heat of vaporisation
The energy absorbed by a substance to change its state from liquid to gas with no change in temperature.
Boyle’s Law
For a system at constant temperature with constant mass, the product of pressure and volume is a constant.PV = NkT providing N and T are constant.
Assumptions of an Ideal Gas
•Collisions between molecules and the container walls are elastic•Force between molecules is negligible except during collisions•Volume of the molecules is negligible compared to the volume of the container•Time within a collision is negligible compared to the time between collisions
Brownian motion
Molecules have random motion due to many collisions with very fast, tiny (unseen) molecules which are moving in random directions.
Temperature
Shows which way heat will flow.
Heat
Thermal energy
Displacement (for oscillations)
The distance and direction of an oscillating object from its rest position.
Amplitude
The maximum displacement of an oscillating object from its rest position
Period
The time taken for an object to make one complete oscillation
Frequency
The number of oscillations of a particle per unit time
Angular frequency
The rate of change of angle expressed in radians per second
Phase difference
The fraction of an oscillation between two oscillating particles expressed in degrees or radians
Path difference
The amount by which two waves are out of step with each other
Simple harmonic motion
Motion of an oscillator whose acceleration is directly proportional to displacement and directed towards the equilibrium position
Newton’s 1st Law
An object will remain at rest or continue to travel at constant velocity unless acted on by an external force
Newton’s 2nd Law
The resultant force on an object is directly proportional to and in the same direction as its rate of change of linear momentum
Newton’s 3rd Law
If body A acts on body B with a force F then body B acts on body A with a force equal in magnitude but opposite in direction to F
Newton’s Law of gravitation
Force is directly proportional to the product of their masses and inversely proportional to the square of their separation.
Newton
The force which gives a mass of 1 kg an acceleration of 1ms^-2
Linear momentum
Mass x velocity = linear momentum
Net force on a body
Rate of change of momentum
Impulse of a force
The product of a force and the time for which it acts OR the change in momentum of an object
Principle of conservation of momentum
In a closed system the total momentum in any direction is conserved.
Perfectly elastic collision
A collision in which both kinetic energy and momentum are conserved
Inelastic collision
A collision in which momentum is conserved but kinetic energy is not
Completely inelastic collision
A collision in which all of the kinetic energy is converted to other forms
Radian
The angle subtended by an arc equal in length to the radius of the circle
Centripetal acceleration
The total acceleration of an object which is undergoing circular motion OR the acceleration towards the centre of the circle.
Centripetal force
The total force acting on an object which is undergoing circular motion OR the resultant force on an object which is travelling in a circle.
Gravitational field strength
The gravitational force per unit mass
Gravitational field
A region in space, which any mass will experience a force of attraction. All masses have a gravitational field around them.
Gravitational Potential
The energy needed to bring a unit point mass from infinity to a given location.
Period (circular motion)
The time to make one complete revolution
Geostationary orbit
The orbit of an artificial satellite with a period of one day that remains above the same point on the Earth’s equator.
Acoustic Impedance
Z = ρc where ρ is the density of the material and c is the speed of ultrasound in the material
Piezoelectric effect
The application of a p.d. across a material / crystal causes an expansion / vibration / contraction
Acoustic impedance matching
The impedances of the media are similar
