AS level definitions Flashcards
Define specific charge
The charge in coulombs divided by the mass in kilograms or charge to mass ratio.
Define an isotope
An atom with a nucleus with the same number of protons but different number of neutrons.
Define the photo-electric effect
The emission of electrons from metal surfaces by incident light of an appropriate frequency.
Define the work function
The minimum energy required for an electron to escape from the surface of the metal.
Define the threshold frequency
The minimum frequency of a photon to produce photoelectrons.
Define “electron volt”
The energy given to an electron when it passes through a potential difference of 1 V.
Define the ionisation energy of an atom
The minimum energy required to remove an electron from an atom in its ground state.
Define the excitation energy
The energy required to move an electron from a lower energy level to a higher energy level.
Define “line spectra”
The characteristic wavelengths of light produced by individual excited atoms.
Define electric current
The number of coulombs of charge passing a point every second.
Define potential difference
The work done per unit charge in moving charges from one point in the circuit to another.
Define electrical resistance
The ratio of the potential difference across a component to the current through it.
Define an ohmic conductor or resistor
The ratio of potential difference to current remains constant.
What is Ohm’s Law?
The current through component is proportional to the potential difference across it.
Define the critical temperature
The temperature at or below which the resistivity of a superconductor becomes zero.
State Kirchoff’s first (current) law
The (vector) sum of currents into a junction equals zero.
State Kirchoff’s second (voltage) law
In any closed loop the sum of the EMF equals the sum of the potential difference.
Define EMF
The total energy supplied per coulomb given to charges as they pass through the battery or cell (before losing
energy to internal resistance).
Define internal resistance
The resistance inside a battery, cell or power supply.
Define useful volts
The potential difference across the terminals of the power supply.
Define lost volts
The potential difference across the internal resistance of the power supply.
Define a scalar quantity
A physical quantity which has magnitude only.
Define a vector quantity
A physical quantity which has magnitude and direction.
State when an object is in equilibrium
When the resultant force on it is zero and the resultant torque is zero.
Define a couple
Two equal and opposite forces separated by a distance D between the lines of action of the forces. (this produces rotational motion only).
Define torque / a moment
The force multiplied by the perpendicular distance from the pivot point to the line of action of the force.
State the principle of moments
For an object in equilibrium the sum of the clockwise moments equals the sum of the anticlockwise moments. This applies about any point which is on or outside the object.
Define “centre of mass”
The point at which the whole mass of the object appears to act.
Define displacement
The distance an object has moved in a particular direction.
What is speed?
The distance travelled by an object divided by the time taken.
What is velocity?
The change in displacement of the object divided by the time taken.
What is acceleration?
The change in velocity divided by the time taken.
Define parabolic path
The shape of the path of a particle moving with a component of motion at right angles to a constant resultant force (constant acceleration).
Give Newton’s First Law
An object remains at rest or moves with a constant velocity providing no resultant external force is applied.
Give Newton’s Second Law
For a constant mass the acceleration of the object is proportional to the resultant force
applied to it (and is inversely proportional to its mass -> a = F/m)
Give Newton’s Third Law
If object A applies a force F object on B, object B applies a force of –F (minus F, i.e. in the
opposite direction) on object A.
Define work
Work done equals force multiplied by the distance moved in the direction of the force.
(The force is being used to move an object)
What is power?
Power equals work done divided by time.
State the principle of conservation of energy
Energy cannot be created or destroyed it can only be changed from one form to another.
Define amplitude
The maximum displacement from the equilibrium position
Define frequency
The number of whole oscillations per second.
Define wavelength
The distance between two consecutive particles in a wave which are in phase.
Define wave speed
The speed of energy transfer through the medium.
Define path difference
The extra distance one of the waves coming from two sources has to travel to reach a point.
(The difference in distance travelled between the waves at a point)
Define electromagnetic wave
A transverse wave, consisting of a changing magnetic field at right angles to a changing electric field.
Define polarised waves
Electromagnetic waves with an electric field vector in one plane only.
Define unpolarised waves
Electromagnetic waves with an electric field vector in many directions.
What is refractive index?
The absolute refractive index of the substance is the speed of light in a vacuum divided by the speed of light in the substance.
Define critical angle
The angle of incidence on a boundary between two media when the angle of refraction is 90°.
(The first media must be denser than the second)
Define total internal reflection
When the angle of incidence is greater than critical angle and all the light is reflected within the substance.
Define “stationary wave”
A stationary wave is formed by two waves of the same frequency and similar amplitude travelling in opposite directions.
Define node
A point on stationary wave with zero amplitude.
Define antinode
A point on stationary wave with maximum amplitude.
Define the fundamental frequency
The lowest frequency of a wave which will produce a stationary wave.
(Produces the first harmonic)
Define coherence
Coherent waves have the same frequency and a constant phase relationship.
Define “fringe spacing”
The distance between two consecutive maxima or minima in an interference pattern.
What is impulse?
Force multiplied by time.
State the principle of conservation of momentum
Momentum in a collision is always conserved providing no resultant external forces are acting.
Define an elastic collision
Kinetic energy is conserved
Define an inelastic collision
Kinetic energy is not conserved
Define an explosion / explosive collision
Kinetic energy is increased due to transfer of energy from the explosion
State Hooke’s Law
The extension of a spring or material is proportional to the tensile force applied (this applies up to the limit of proportionality of the material).
Define “elastic limit”
The point beyond which a material or spring stretched when it will not return to its original length.
Define tensile stress
Tensile force divided by cross-sectional area of the material.
Define tensile strain
Extension divided by original length.
What is plastic behaviour?
A material undergoing plastic behaviour will not return to its original shape after deforming forces are removed.
Define fracture
This is when the material breaks. Materials are compared by their ultimate tensile stress, this is the tensile stress needed to break the material (strength of material).
Define brittleness
A brittle material will not undergo plastic deformation before fracture.
What is the Young Modulus?
Tensile stress divided by tensile strain.
