Definitions Flashcards
Young’s modulus
Young’s modulus is stress divided by strain
Work done
The force causing a motion multiplied by the distance travelled in the direction of the motion. (Equal to the energy transferred)
Stress
Stress is the force per unit cross-sectional area
Strain
The extension per unit length
Spring constant
The force per unit extension
Resistivity
The resistance of a wire of the material of unit length
Refraction
The change in direction of a wave at the boundary between materials, caused by the speed of the wave.
Power
The energy transferred per second
Diffraction
The spreading of a wave when it meets an obstacle into regions where it would not be seen if it only moved in straight lines
Potential difference (P.d.)
The potential difference between two points is the amount of electrical energy transferred to other forms of energy when 1 coulomb of charge flows between the two points
Polymeric solid
Made up of long chain-like molecules. No long range order between molecule’s but order within molecule’s
OHM’s law
The current flowing through a metal wire at constant temperature is directly proportional to the potential difference across it
Mean velocity
The average measured velocity over a significant amount of time.
V = x/t
Mean speed
The average measured speed over a significant amount of time.
s = d/t
Mean acceleration
The average measured acceleration over a significant amount of time. a = Δv/t
Hooke’s law
The tension in a spring or wire is directly proportional to its extension from its natural length, provided the extension is not too great
Electrical current
The rate of flow of charge
Crystal solid
Atoms are arranged in a regular array (lattice). There is no long range order
Brittle material
A material with no region of plastic deformation. Under tension, it breaks by brittle fracture, caused by crack propagation
Amorphous solid
Atoms are arranged quite randomly such that they have no long-range order but they may have short range-order
Transition temperature
The temperature at which a material when cooled, loses all its electrical resistance and becomes super-conducting
Electro motive force (EMF)
The electro motive force of a source is the energy converted from some other form to electrical potential energy per coulomb of charge flowing through the source
Snell’s law
At the boundary between any two given materials, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant
Scalar
A quantity that has only magnitude
Vector
A quantity that has magnitude and direction
Moment
The product of force and the perpendicular distance between the line of action of the force and the pivot.
Newtons 1st law
If the resultant force on an object is zero then the object will either remain stationary, or if it was already moving, then it will to continue to move with uniform velocity
Newtons 2nd law
The rate of change of momentum of a body is directly proportional to the force applied. Which takes place in the direction of the force.
Newtons 3rd law
If body A exerts a force on body B, then body B exerts and equal but opposite force on body A.
Density
The mass per unit volume
Progressive Wave
Is a pattern of disturbances travelling through a medium and carrying energy with it, involving the particles of the medium oscillating about their equilibrium position. It does not involver the transfer of matter.
Transvers Waves
The oscillations of the particles are at right angles to the direction of travel of the wave
Longitudinal waves
The oscillations of the particles are in line with or parallel to the direction of travel of the wave
Wavelength
Is the minimum distance between two points on the wave oscillating in phase
Frequency
Is the number of cycles of a wave that pass a given point in one second
Amplitude
Is the distance from the middle of the wave to the crest or the trough, the greater the amplitude the more energy the wave is carrying
Speed of a wave
Is the distance travelled by the wave in one second
Phase
Is a term used to describe the relationship between the pattern of vibration of two points on a wave
Polarised wave
Is a transverse wave in which particle oscillations occur in only one of the directions at right angles to the direction of wave propagation
Principle of superposition
States if the waves from two sources occupy the same region then the total displacement at a point is the vector sum of the displacements of the individual waves at that point
Coherent
Means that there is a constant phase difference
Stationary Waves …
Are produced from the superposition of two progressive waves of equal amplitude and frequency travelling in opposite directions
Monomode fibres
Is where the core diameter is so small that the path possible through the fibre is along its axis
Photon
Is a discrete packet of energy, showing both particle and wave properties
Electronvolt
Is the energy of an electron accelerated by a potential difference of one volt
Photoelectric effect
When light or ultraviolet radiation of short enough wavelength falls on a surface, electrons are emitted from the surface
Threshold frequency
Is the minimum frequency of a photon that will cause emission of an electron from a particular metal surface
Black Body
Is a body or surface which absorbs all electromagnetic radiation that falls upon it. Nothing is a better emitter of radiation at any wavelength than a black body at the same temperature
Conservation of Baryon Number
In any interaction between particles in a system the total baryon number in the system must not change
Conservation of Lepton Number
In any interaction between particles in a system the total lepton number in the system must not change
