Definitions Flashcards
Isotope
Isotopes are atoms with the same number of protons but difference numbers of neutrons
Pair Production
When a photon decays and creates a particle and its corresponding anti-particle near to a nucleus
Leptons
Leptons interact through the weak nuclear force and the electromagnetic force if they are charged these are fundamental
Hadrons
Hadrons interact through the strong nuclear force and the electromagnetic force if they are charged. Apart from the proton, Hadrons decay through the weak interaction
Baryons
Are particles that contain 3 quarks. Protons are hadrons and all other hadrons decay into protons
Mesons
Are Hadrons that contain a quark and an anti-quark and do not include protons in their decay products.
Strangeness
Always conserved in a Strong interaction, particles that contain Strange or anti-strange quarks
Energy, Momentum, Charge, Baryon number and Lepton number
Are always conserved
Work Function
The minimum energy required by an electron to escape from a metal surface
Threshold Frequency
The minimum frequency of radiation of a photon required to release an electron from a metal surface
Ionisation
The energy required to remove an electron from an atom from the ground state.
Electron-volt
The work done on an electron accelerating it through a potential difference of one volt.
Fluorescence
Materials that absorb UV radiation and when the electrons de-excite they release photons of visible frequencies
Potential Difference
The work done per unit charge
Electro-motive force
The electrical energy produced per unit charge passing through the source
Ohm’s Law
The potential difference across a metallic conductor is proportional to the current through it provided the physical conditions do not change
Resistivity
The resistance of a material of length l and cross sectional area A
Critical Temperature
A material that has zero resistivity below the critical temperature is a superconductor
Kirchoff’s first law
The sum of the currents going into a junction equals the sum of the currents coming out of the junction
Kirchoff’s second law
The sum of the emfs equals the sum of the pds in any closed loop
Power
Rate at which energy is transferred
Internal resistance
The internal resistance of a source is the loss of potential difference per unit current in the source when the current passes through the source
Vector
Any physical quantity that has a direction as well as a magnitude
Moment
The moment of a force about any point is defined as the force x the perpendicular distance from the line of action of the force to the point
Principle of moments
The sum of the anticlockwise moments equals the sum of the clockwise moments about any pivot
Centre of mass
The centre of mass of a body is the point through which a single force on the body has no turning effect
Equilibrium
A body is in equilibrium when the resultant force acting on the body is zero and the sum of all the turning moments are zero
Acceleration
Defined as the change in velocity per unit time
Displacement
The distance in a given direction from a certain point
Newton’s first law of motion
Objects either stay at rest or remain in uniform motion unless acted on by a force
Newton’s second law of motion
The rate of change of linear momentum is directly proportional to the resultant force applied
Newton’s third law of motion
For every force there is another force which is equal in size, opposite in direction, acts on the same line of action and is the same type of force. The two forces act on different bodies
Resultant force
The sum of all the forces acting on a body
Principle of energy conservation
Energy cannot be created or destroyed
Work done
The energy transferred to an object equal to the product of the force and the distance moved in the direction of the force
Efficiency
The useful energy out/total energy in
Density
The mass per unit volume
Hooke’s Law
The force needed to stretch a spring is directly proportional to the extension of the spring from its natural length
Limit of proportionality
The point up to which the stress on an object is directly proportional to the strain
Elastic limit
The point past which a spring will not return to its original length
Tensile Stress
The force per unit area on a material
Tensile Strain
The extension of a material divided by its original length
Ductile
A material that extends with little stress
Young’s Modulus
The tensile stress divided by the tensile strain
Brittle
A material that undergoes very little strain
Transverse waves
A wave whose oscillations are perpendicular to the direction of motion
Longitudinal waves
A wave whose oscillations are parallel to the direction of motion
Amplitude
The maximum displacement from equilibrium
Wavelength
The distance between two particles with the same displacement and same velocity
Frequency
The number of cycles or number of waves to pass a point per second
Time period
Time taken to complete one cycle
Principle of superposition
When two waves meet the total displacement at a point is equal to the vector sum of the individual displacements at that point
Coherent
Two waves with the same frequency/wavelength and constant phase difference
Stationary wave
Usually formed from a wave and its reflection, superposing and forming areas of maximum (Antinode) and no displacement (Node)
Refraction
When a wave passes from one medium to another, changing direction and speed
Bright fringe
Formed when two waves overlap and reinforce
Dark fringe
Formed when two waves meet and cancel out because one wave is 180° out of phase
