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# Laws

### Laws in Physics

Term | Definition | continued |
---|---|---|

Laws of reflection of light | 1.The incident ray the reflected ray and the normal at the point of incidence all lie in the same plane 2.The angle of incidence is equal to the angle of reflection | |

Concave mirror | 1.If the object is outside the focus it's real and located in front of the mirror 2.If the object is inside or at the focus, it's virtual and located behind the mirror | |

Convex mirror | 1.The image is always virtual and located behind the mirror 2.The image is always diminished. The nearer the object to the mirror, the bigger the image | |

Laws of Refraction of light | 1.The incident ray the refracted ray and the normal at the point of incidence all lie in the same plane 2.The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant sini/sinr=n | |

Convex lens | 1.If the object is outside the focus the image is real inverted and located at the opposite side to the object 2.If the object is inside the focus the image is virtual upright and located on the same side of the lens as the object | |

Newton's 1st Laws of Motion | every body will remain in a state of rest or travelling with a constant velocity unless an unbalanced external force acts on it | |

Newton's 2nd Laws of Motion | when an unbalanced force acts on a body the rate of change of a body's momentum is directly proportional to the force and takes place in the direction of the force | |

Newton's 3rd Laws of Motion | if a body A exerts a force on body B then body B exerts an equal but opposite force on body A | |

The principle of conservation of momentum | in any interaction between two or more bodies, the total momentum of the bodies before the interaction is equal to the total momentum after the interaction provided no external forces act on the system of bodies | |

Archimedes' Principle | when an object is partially or completely immersed in a fluid it experiences an upthrust equal in magnitude to the weight of the fluid displaced | |

The Laws of floatation | the weight of a floating body is equal to the weight of the fluid displaced | |

Boyle's Law | at a constant temperature the volume of a fixed mass of gas is inversely proportional to its pressure | |

Newton's Law of Universal Gravitation | any two point masses in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between | |

Laws of equilibrium | 1.The vector sum of the forces in any direction is zero 2.The sum of the moments about any point is zero | |

Principle of conservation of energy | states that energy cannot be created or destroyed but can only be converted from one from to another | |

Hooke's Law | when an object is bent, stretched or compressed by a displacement s, the restoring force F is directly proportional to the displacement provided the elastic limit is not exceeded | |

Simple Harmonic motion | 1.Its acceleration is directly proportional to its distance from a fixed point on its path 2.Its acceleration is always directed towards that point | |

Frequency and wavelength of a stationary wave | 1.The frequency of vibrating particles in a stationary wave is the same 2.The frequency of a stationary wave is the same as the frequency of the travelling wave producing it | 3.If λ is the wavelength of the travelling waves causing the stationary wave then: *distance between two consecutive nodes= λ/2 *distance between two consecutive antinodes=λ/2 *distance between an antinode and the next node= λ/4 |

Doppler effect | the apparent change in the frequency of waves due to the motion of the source or the observer *f'>f- towards *f'<f- away | |

Coulomb's Law | the force of attraction or repulsion between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them | |

Joule's Law | states that the rate at which heat is produced in a conductor is directly proportional to the square of the current provided its resistance is constant | |

The Right-hand grip rule | states that if the right-hand clasps a conductor with the thumb pointing in the direction of the current the the fingers give the direction of the magnetic field around the conductor | |

A current-carrying conductor in a magnetic field | will always experience a force unless the conductor is parallel to the magnetic field. The direction of the force is always: *perpendicular to the current and *perpendicular to magnetic field | |

Fleming's Left-hand rule | if the thumb first and second finger (left) are held at right angles with the first finger pointing in the direction of the magnetic field and the second finger pointing in the direction of the current, then the thumb points in the direction of the force | |

Lenz's Law | the direction of an induced current is always such as to oppose the charge producing it |