Definitions Flashcards
electric current
the rate of flow of electric charge
p.d.
the p.d. between two points is the energy converted from electrical potential energy into some other form per coulomb of charge
ohms law
the current flowing through a wire at a constant temperature is proportional to the p.d. across it
electrical resistance
the resistance of a conducted is the p.d. across it divided by the resulting current
resistivity, P
the resistance, R, of a metal wire of length, L, and cross sectional area, A, is given by R=PL÷A in which P, the resistivity is a constant (at a constant temperature) for the material of the wire
superconducting transition temperature
the temperature at which a material when cooled loses all its electrical resistance and becomes superconducting
law of conservation of charge
electric charge cannot be created or destroyed, though positive and negative charges can neutralise each other. charge cannot pile up anywhere
e.m.f
the e.m.f of a source is the energy converted from some other form (e.g. chemical) to electrical potential per coulomb of charge flowing through the source
progressive wave
a pattern of disturbances travelling through a medium and carrying energy with it, involving the particles of the medium oscillating about their equilibrium positions
transverse wave
a transverse wave is one where the particles oscillations are at right angles to the direction of travel of the wave
longitudinal wave
a longitudinal wave is one where the particles oscillations are parallel to the direction of travel of the wave
polarised wave
a polarised wave is a transverse wave in which the particle oscillations occur in only one of the directions at right angles to the direction of the movement of the wave
wavelength of a progressive wave
the minimum distance between two points on the wave oscillating in phase
frequency of a wave
the number of cycles of a wave that pass a given point in one second
the principle of superposition
the principle of superposition states that if waves from two sources occupy the same space then the total displacement at any one point is the vector sum of the individual displacements
in phase
waves arriving at a point are said to be in phase if they have the same frequency and are at the same point in their wave cycle.
phase difference
phase difference is the difference in position of 2 points within a cycle of oscillation. one cycle = 360 degrees or 2 pi
quantity
a quantity is represented by a number x a unit
Scalar
a scalar is a quantity with magnitude only
vector
a vector is a quantity with both direction and magnitude
force
a force on a body is a push or pull acting on the body from an external force
newton’s third law
if body A exerts a force on body B then body B will exert and equal and opposite force on body A
sigma F=MA (newton’s second law)
the mass of a body x it’s acceleration is equal to the vector sum of the forces acting on the body. this vector sum is called the resultant force
density of a material
density is an objects mass÷volume
moment of a force
the moment of a force about a point is defined as the force x the perpendicular distance from the point to the line of action of the force
the principle of moments
for a system to be in equilibrium the moment clockwise must be equal to the moment anticlockwise
centre of gravity
the centre of gravity is the point within a body at which we can consider all the weight is acting upon
displacement
the displacement of point B from point A is the shortest distance from A to B with the direction
work
the work done by a force is the product of the magnitude of the force and the distance moved in the direction of the force
energy
the energy of a body or system is the amount of work it can do
principle of conservation of energy
energy cannot be created or destroyed, only transferred from one form to another. energy is a scalar
potential energy
potential energy is energy possessed by virtue of position
kinetic energy
kinetic energy is energy possessed by virtue of its motion
power
power is the work done per second or energy transferred per second
isotope
isotopes are atoms with the same number of protons but different number of neutrons in the nuclei
momentum
the momentum of an object is its mass multiplied by its velocity
