# PHY (definitions)

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

## Section

Question | Answer |
---|---|

displacement | distance travelled along a specified direction |

speed | rate of change of distance |

velocity | rate of change of displacement |

acceleration | rate of change of velocity |

newton's first law | a body remains in its state of rest or uniform motion in a straight line unless acted upon by a resultant force |

newton's second law | the 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 law | if body A exerts a force on body B, then body B exerts an equal and opposite force on body A |

mass | property of a body that resists change in motion |

weight | the gravitational force acting on a mass |

momentum | product of mass and velocity (p=mv) |

force | rate of change of momentum |

impulse | product of the force acting on a body and the time interval during which the force is exerted (impulse= ft) |

principle of conservation of momentum | states that the total momentum of a system of objects remains constant provided no resultant external force acts on the system |

hooke's law | states 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 |

torque | of a couple is the product of one of the forces and the perpendicular distance between their lines of action |

work | product of the force F and the displacement s made in the direction of the force |

power | rate of doing work |

work-energy theorem | states 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 wave | a progressive wave travels from one point to another resulting in a transfer of energy |

transverse waves | waves in which the displacement of the particles is perpendicular to the direction of energy transfer. all EM waves are transverse waves |

longitudinal waves | waves in which the displacement of the particles is parallel to the direction of energy transfer. all sound waves are transverse waves |

frequency | is the number of complete cycles per unit time |

period | is the time taken for an particle in the wave to complete one oscillation |

wavelength | is the distance travelled by the wave in one period |

speed of a wave | is the distance the wave moves per unit time. |

phase difference | is 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 |

wavefront | a line or surface joining points of a wave that are in phase |

intensity of a wave | is the rate of energy flow per unit cross-sectional area perpendicular to the direction of wave propagation |

principle of superposition | when 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 waves | when 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 waves | are waves that have constant phase difference between them |

interference | occur when waves from 2 or more waves of the same kind meet at a point and superpose to produce a resultant wave |

path difference | the difference in path lengths of two waves which result in constructive or destructive interference |

magnetic flux density | at 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 |

tesla | one 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 |

charge | product 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 |

volt | is 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 |

resistance | across a device is the ratio of the potential difference across it to the current flowing through it |

ohm | is 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 effect | is the emission of electrons from a metal surface when electromagnetic radiation of sufficiently high frequency is shone on it |

threshold freqeuncy | is 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 metal | is the minimum energy needed to remove an electron from the metal surface |

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