# PHY (definitions)

yaranigu's version from 2017-03-12 07:17

## Section

displacement distance travelled along a specified direction
speedrate of change of distance
velocityrate of change of displacement
accelerationrate of change of velocity
newton's first lawa body remains in its state of rest or uniform motion in a straight line unless acted upon by a resultant force
newton's second lawthe rate of change of momentum of a body is proportional to the resultant force acting on it and the change takes place in the direction of the force
newton's third lawif body A exerts a force on body B, then body B exerts an equal and opposite force on body A
massproperty of a body that resists change in motion
weight the gravitational force acting on a mass
momentumproduct of mass and velocity (p=mv)
forcerate of change of momentum
impulseproduct of the force acting on a body and the time interval during which the force is exerted (impulse= ft)
principle of conservation of momentumstates that the total momentum of a system of objects remains constant provided no resultant external force acts on the system
hooke's lawstates that within the limit of proportionality, the extension x produced in a material is directly proportional to the load F applied
moment the moment of a force is defined as the product of the force and the perpendicular distance between the axis of rotation and the line of action of the force
torqueof a couple is the product of one of the forces and the perpendicular distance between their lines of action
workproduct of the force F and the displacement s made in the direction of the force
powerrate of doing work
work-energy theoremstates that the work done by the resultant external force acting on a particle is equal to the change in total mechanical energy of the particle
progressive wavea progressive wave travels from one point to another resulting in a transfer of energy
transverse waveswaves in which the displacement of the particles is perpendicular to the direction of energy transfer. all EM waves are transverse waves
longitudinal waveswaves in which the displacement of the particles is parallel to the direction of energy transfer. all sound waves are transverse waves
frequencyis the number of complete cycles per unit time
periodis the time taken for an particle in the wave to complete one oscillation
wavelengthis the distance travelled by the wave in one period
speed of a waveis the distance the wave moves per unit time.
phase differenceis the measure, in angular form, of the fraction of a cycle two particles in a wave or two waves are out of step by in their motion
wavefronta line or surface joining points of a wave that are in phase
intensity of a waveis the rate of energy flow per unit cross-sectional area perpendicular to the direction of wave propagation
principle of superpositionwhen two or more waves of the same kind exist simultaneously at a point in space, the resultant displacement of the waves at any point is the vector sum of the displacements due to each wave acting independently
standing waveswhen two progressive waves of equal frequency travelling with the same speed in opposite directions are superposed, a stationary or standing wave is formed
diffraction is the bending or spreading of waves when they pass an obstacle or an aperture
coherent wavesare waves that have constant phase difference between them
interferenceoccur when waves from 2 or more waves of the same kind meet at a point and superpose to produce a resultant wave
path differencethe difference in path lengths of two waves which result in constructive or destructive interference
magnetic flux densityat a point id defined as the force acting per unit current per unit length of the conductor when the conductor is placed at right angles to the field
teslaone tesla is the uniform magnetic flux density which, acting normally to a long straight wire carrying a current of 1 ampere, causes a force per unit length of 1N/m on the conductor
chargeproduct of the current flowing through a cross section of a circuit and the time taken
electric current is the rate of flow of charged particles
coulumb the amount of charge that passes a point when a current of one ampere flows for one second
voltis the p.d across a device in a circuit if one joule of electrical energy is converted to other forms of energy per coulumb of charge passing through it
resistanceacross a device is the ratio of the potential difference across it to the current flowing through it
ohmis the resistance of a device when the potential difference across it is one volt per ampere of current flowing through it
potential difference (energy)across an electrical device is the amount of electrical energy converted to other forms of energy per unit charge passing through it (V=W/Q)
potential difference (power)across an electrical device is defined as the power delivered to the device per unit current passing through it (V=P/I)
e.m.f (source)of a source is defined as the energy converted from other forms into electrical energy per unit charge passing through it (E=W/Q)
e.m.f (driving unit charge)the energy transferred by a source in driving unit charge round a complete circuit (E=P/I)
photoelectric effectis the emission of electrons from a metal surface when electromagnetic radiation of sufficiently high frequency is shone on it
threshold freqeuncyis the minimum frequency of the electromagnetic radiation below which no electrons are emitted from the metal surface regardless of the intensity of the radiation
work function of a metalis the minimum energy needed to remove an electron from the metal surface