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Physics Definitions

7 pages, 103 questions, 4 questions with responses, 12 total responses,    1    0
Yash Khasgiwala
Children's Academy, Bachani Nagar, Malad East, Mumbai
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1. Force is a physical cause which changes or tends to change the shape or size or state of rest or state of motion of a body. 2. Force (F = ma) (Vector) Contact force 3. Non-Contact force Forces experienced by bodies without being physically touched. 4. Gravitational force Each particle in the universe attracts each other by a force due to its mass which is called as Gravitational force. 5. Force of gravity or Weight of body The force on a body due to earth s attraction. 6. Electro static force The two like charges repel while 2 unlike charges attract each other. The force between the charges is called as Electro static force 7. Magnetic force 8. General character of non-contact force 9. Newton s 1st law of motion 2 like magnetic poles repel while 2 unlike magnetic poles attract each other. The force between magnetic poles is called as Magnetic force Gravitational force is always attractive in nature while electro static force and magnetic force can be either attractive or repulsive. The magnitude of non-contact force is inversely proportional to square of distance of separation between 2 bodies. A body continues to be in a state of rest or in a state of motion unless an external force is applied on it. 10. Newton s 2nd law of motion F= p/ t Rate of change of momentum is directly proportional to the force applied and this change in momentum takes place in the direction of applied force. 11. Newton s 3rd law of motion Every action has an equal and opposite reaction. 12. Inertia (directly proportional to mass) SI unit is kg m/s Linear momentum (p = mv) (vector qty) Inherent property of a body to resist the change in state of rest or state of motion of body. One dyne (1 dyne=1g x 1cm/sec sq) One Newton (1 newton = 1 kg x 1 m/sec sq) One Kilogram force (9.8 N) One dyne is the force applied on a body of mass one gram to produce an acceleration of 1 cm/sec. sq One Gram force (980 dyne) Force of gravity on a mass of 1 Gram. 13. 14. 15. 16. 17. Forces which are applied on body by making a physical contact. The momentum of body in linear motion is the product of its mass and velocity. One newton is the force applied on a body of mass one kilogram to produce an acceleration of 1 m/sec. sq Force of gravity on a mass of 1 Kg. 18. 19. Moment (vector quantity) (Newton metre) Couple Moment of a force is equal to the product of magnitude of force and perpendicular distance of line of action of force from the axis of rotation. Two equal and opposite parallel forces not acting along the same line form a couple. 20. Moment of couple 21. Equilibrium Moment of couple is equal to the product of either force and the perpendicular distance between the line of action of both the forces. (couple arm) When a number of forces acting on a body produce no change in its state of rest or motion then the body is said to be in Equilibrium. 22. Static Equilibrium When a number of forces acting on a body produce no change in its state of rest then the body is said to be in Static Equilibrium. 23. Dynamic Equilibrium When a number of forces acting on a body produce no change in its state of motion then the body is said to be in Equilibrium. 24. Centre of gravity (depends on the shape of the body) 24. Centrifugal force Centre of gravity of a body is the point about which the algebraic sum of moment of weight of all the particles constituting the body is zero. OR The point about which weight of all the particles of body acts. Force acting away from the centre 25. Centripetal force Force acting towards the centre of a circular path. 26. Work (Joule) (scalar quantity) Work is said to be done only when the force applied on the body makes the body move. 27. One Joule (1 J = 1 N x 1 m) One Joule of work is done when one Newton of force moves the body through a distance of 1 metre. 28. One Erg (1 erg = 1 dyne x 1 cm) Power (Watt) (scalar quantity) (1 HP = 746 W) Watt One Erg of work is done when one dyne of force moves the body through a distance of 1 centimetre. 31. Energy (scalar quantity) Capacity of a body to do work. 32. Watt hour (1 Wh = 3600 J) Energy spent is 1 Watt hour by a appliance of 1 watt in 1 hour. 33. One Kilowatt hour Energy spent is 1 Kilowatt hour by a appliance of 1 kilowatt in 1 (1 kWh = 3600000 J) hour. 34. Electron Volt (1 eV = 1.6/10000000000000 29. 30. Rate of doing work The power spent is 1 watt when 1 Joule of work is done in 1 second. One Electron Volt is the energy gained by an electron when it is accelerated through a potential difference of 1 volt. 000000 J) 35. Mechanical energy Energy possessed by a body due to its state of rest or state of motion. 36. Kinetic energy Energy possessed by a body due to its state of motion. 37. Potential energy Energy possessed by a body due to its changed position or configuration. 38. Work energy theorem Work done by a force on a moving body is equal to the increase in kinetic energy. 39. Translational kinetic energy The kinetic energy of a body due to its motion in straight line path. 40. Rotational kinetic energy The kinetic energy of a body due to its rotational motion. 41. Vibrational kinetic energy The kinetic energy of a body due to its vibrational motion. 42. Gravitational potential energy The potential energy of a body due to force of attraction of earth. 43. Energy degradation Gradual decrease of useful energy due to radiation loss or friction. 44. Refraction of light 45. Laws of refraction 46. No refraction The change in direction of the path of light, when it passes from one transparent medium to another transparent medium, is called refraction. The incident ray, the refracted ray and the normal at the point of incidence, all line in the same plane. The ratio of the sine of angle of incidence (i) to the sine of angle of refraction (r) is constant for the pair of given media. This constant is called the refractive index of the second medium with respect to first medium. Sin i = 1 2 or 2n1 Sin r Angle of incidence is 0 Refractive index of 2 mediums is equal. 47. Lateral displacement 48. Absolute refractive index 49. Refractive index The perpendicular distance between the path of emergent ray and the direction of incident ray is called lateral displacement. 1. directly proportional to the angle of incidence. 2. directly proportional to the thickness of the slab. 3. directly proportional the refractive index of the material of the slab. 4. inversely proportional to the wavelength of light. Refractive index of a medium defined with respect to air. The ratio of the sine of angle of incidence (i) to the sine of angle of refraction (r) is constant for the pair of given media. This constant is called the refractive index of the second medium with respect to first medium. 50. Prism A prism is a transparent refracting medium bounded by five plane surfaces inclined at some angles. 51. Angle of prism The angle between two refracting surfaces is called angle of prism. 52. Angle of deviation The angle between the direction of incident ray and the emergent ray is called the angle of deviation. 1. Angle of incidence: As the angle of incidence increases the angle of deviation decreases. However at a particular angle of incidence, the angle of deviation is minimum. In the minimum deviation position, angle of incidence = angle of emergence. Beyond this angle of incidence, the angle of deviation increases. 2. Refractive index of material: As the refractive index of material increase, the angle of deviation also increases. 3. Wavelength or colour of light: Angle of deviation in case of violet colour (least wavelength) is more than angle of deviation for red colour (large wavelength). 4. Angle of prism: As angle of prism increases, angle of deviation also increases. 53. 54. Shift Critical angle 1. directly proportional to the thickness of the denser medium. 2. directly proportional to the refractive index of the material of the slab. 3. inversely proportional to the wavelength of light. Critical angle is the angle of incidence in the denser medium corresponding to which the angle of refraction in the rarer medium is 900 . 1. inversely proportional to the refractive index. 2. directly proportional to temperature. A ray of light in a denser medium is incident at the surface of the rarer medium such that angle of incidence is greater than the critical angle for a given pair of media then the ray is totally reflected back in a denser medium. A total reflecting prism suffers total internal reflection inside the prism when the light is incident normally on any of its faces. 450 -900 450 prism is called a total reflecting prism. Lens is a transparent refracting medium bounded by two curved surfaces which are generally spherical. 55. Total Internal Reflection 56. Total reflecting prism 57. Lens 58. Second Focus of a convex lens It is a point on the principle axis such that the rays of light, incident parallel to the principle axis pass after refracting through the lens. 59. Second Focus of the concave lens It is a point on a principle axis from which, the rays of light incident parallel to the principle axis, appear to come from after refracting through the lens. 60. First Focus of a convex lens It is a point on a principle axis such that rays of light coming from it after refraction from the lens become parallel to the principle axis. 61. First Focus of the concave lens 62. Optical centre 63. Centre of curvature It is a point on a principle axis such that incident rays of light appearing to meet at it after refraction from the lens become parallel to the principle axis. It is a point on the principal axis of the lens such that a ray of light passing through this point emerges parallel to its direction of incidence or passes undeviated or undisplaced. Centre of the sphere of which the lens is a part of. 64. Radii of curvature Radius of the sphere of which the lens is a part of. 65. Focal length 66. Dispersion Distance between the focus and the optical centre. 1. Lens placed in water then the focal length increases. 2. Thick lens has less focal length than thin lens. The phenomenon of splitting of white light by a prism into its constituent colours. 67. Spectrum The band of 7 colours seen on passing white light through a prism. 68. Scattering Process of absorption and re emission of light energy. 69. Pure note Pure note is a sound of single frequency. 70. Amplitude Maximum displacement of a particle of a medium about its mean position. 71. Time period Time taken by a particle of a medium to complete one vibration. 72. Frequency (Objective) Number of vibrations made by a particle of a medium in one second. 73. Wavelength Distance travelled by a wave in one time period of vibration of particle of a medium. 74. Wave velocity Distance travelled by a wave in one second. 75. Longitudinal waves (Solid liquid gas) Vibration of particle of a medium along the direction of propagation of wave thus forming compression and rarefaction in the medium. 76. Vibration of particle of a medium normal to the direction of propagation of wave forming crest and troughs 77. Transverse waves (solid, surface of liquid) Echo 78. Free vibration Periodic vibration of a body of constant amplitude in the absence of any external force on it. The sound heard after reflection from a distant obstacle after the original sound has ceased. 79. Damped vibration Periodic vibration of a body of decreasing amplitude in the presence of a resistive force. 80. Forced vibration Vibration of a body which takes place under the influence of an external periodic force acting on it. 81. Resonance 82. Loudness (Subjective) Resonance is a special case of forced vibration. When frequency of an externally applied periodic force on a body is equal to its natural frequency then the body begins to vibrate with a increased amplitude. Loudness is the property by virtue of which a loud sound can be distinguished from a faint sound both having same pitch and quality. 83. Pitch (Subjective) Pitch is a characteristic of sound by which a acute note can be distinguished from a grave or a flat note. 84. Quality Quality of a sound is a characteristic which distinguishes two sounds of same loudness and pitch but emitted by two different instruments. 85. Decibel One dB is defined as the change in level of loudness when intensity of sound changes by 26%. 86. Intensity (Objective) (Watt per metre sq) Current (Ampere) Intensity of a wave at a point of the medium is measured as the amount of sound energy passing per second normally through unit area at that point. Amount of charge passing per second through a unit area of a conductor in one second. Electric potential Electrical state of a conductor which determines the direction of flow of charge when 2 conductors are either kept in contact or joined by a metallic wire. 87. 88. 89. 90. Potential (Scalar quantity) (Volt) Potential difference Depends on size, shape, concentration of charges on the conductor. Amount of work done in bringing a unit positive charge from infinity to that point. Amount of work done in moving a unit positive charge from one point to another. 91. Resistance (Ohm) Obstruction offered to the flow of current by a conductor. 92. Ohm s Law 93. Ohmic resistor Current flowing in a conductor is directly proportional to the potential difference applied across its ends provided that the physical conditions and temperature of the conductor remain constant. Conductor which obeys Ohm s Law. Eg. Dilute sulphuric acid, nichrome and copper sulphate solution with copper electrodes. 94. Non-Ohmic resistor Conductor which do not obey Ohm s Law. Eg. Diode valve, Triode valve, junction diode and filament of bulb. 95. Super conductor Substance of zero resistance at a very low temperature. Eg. Mercury below 4.2K. 96. Resistivity (Ohm metre) Resistivity of a material is the resistance offered by a wire of that material of unit length and unit area of cross section. 97. EMF 98. Terminal voltage 99. Voltage drop Energy spent or work done per unit charge in taking a positive charge around the complete circuit of the cell. Depends on material of electrode, electrolyte used. Does not depend on distance between electrode, amount of electrolyte and shape of electrode. Energy spent or work done per unit charge in taking a positive charge around the circuit connected across the terminal of the cell. Energy spent or work done per unit charge in taking a positive charge through the electrolyte of the cell. 100. Internal resistance Obstruction offered by the electrolyte to the flow of current. 101. Electric Fuse Safety device which is used to prevent flow of excessive current in the circuit. 102. Switch On off device for a current in a circuit.

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