Definitions of 250 Physics terms

PHYSICS DEFINITIONS

(The nature of the nature is same for all of us only those who contemplate became extraordinary in discovering Physics)

Dr. Sajid

Ali Talpur

Chapter 1

Physics Definitions: 1 Dr. Sajid Ali Talpur

The Scope of Physics

(You can neither stop nor save the time but can make every moment historical if you know the value of time…!)

1. Physics: - It is the branch of science that deals with the study of matter and energy and their mutual interactions between them. OR

“THE STUDY OF NATURE OF THE NATURE IS CALLED PHYSICS”

2. Energy: - the ability/capacity to do work is called energy.

3. Work: - work is said to be done on a body when, by applying force it attains some displacement.

4. Force: - it is the agency that changes or tries to change the state of rest or motion of the

body.

5. Mechanics: - mechanics is the branch of physics that deals with the bodies in rest or motion

under forces.

6. Fundamental quantity: - the quantity, which cannot be resolved into more fundamental quantities.

7. Derived quantity: - quantities, which are, expressed as some combination of fundamental quantities.

8. Proportional quantities: - such these quantities are dependent on each other; the change in one quantity causes the change in another quantity.

9. Directly proportional quantities: - the quantities in which increase in the amount of one quantity results in the increase of other quantity and the decrease in one quantity affects the reduction in another quantity.

10. Inversely proportional quantities: - in such a case the increase in the amount of one quantity leads to the decrease of the other quantity and vice versa.

11. Constant of proportionality: - when proportionality sign is removed, the “=”sign is applied only after putting a constant that is determined experimentally and is called constant of proportionality.

12. System of units: - a set of fundamental and derived units is called a system of units.13. Mean solar day: - a mean solar day is the time interval between two successive overhead

appearances of the sun.


14. Second: - it is the duration in which Cesium CS133 atom completes 9192631770 transitions

between two hyperfine levels.

15. Meter: - it is the path/distance covered by light or the object moving with the speed of light in 1/c seconds (c= 3*108).

16. Ampere: - one ampere is the amount of current, witch if maintained in two straight conductors of infinite length and negligible area of cross section and placed one meter apart in space would exert a force of 2*10-8 on each other.

17. Kelvin: - It is 1/273. 16 of the thermodynamic temperature of the triple point of water. (Triple point is the temperature where all the three states of water co-exist)

18. Mole: - the gram atomic mass, gram molecular mass or gram formula mass of any substance, which contains 6.02*1023 particles

19. Kilogram: - one kilogram is the mass of the platinium-irradium cylinder at 0 C kept at BIPM near Paris.

20. Dimension: - it is use to denote the nature of the physical quantities.

Chapter 2

Scalars and Vectors

(From e-mail to ship to sail the mediums of waves and water are to avail, for you not to fail with every alarming bell the mediums of maintenance of knowledge, confidence and tolerance are to avail)

21. Scalars: - physical quantities which don’t have direction but only magnitude and a suitable unit

22. Vectors: - the physical quantities, having both the direction and magnitude.

23. Particle: - an object of negligible size and constant mass is referred to as “particle” or “body”. This idea represents a simple model of a real physical situation.

24. Resultant vector: - it is the vector, obtained as a result of the combination of vectors.

25. Component vector: - when a vector acts on a body it may be splited into two or more vectors, called “component vectors”. Generally a vector is resolved into its rectangular components.

26. Rectangular components of a vector: - the components of a vector, which are inclined at the angle of 90.


27. Unit vector: a vector whose magnitude is one is called unit vector.

28. Null vector: - a null vector is that vector whose magnitude is zero.

29. Free vector: - a free vector is that vector which can be displaced parallel by itself and applied to any point.

30. Position vector: - a position vector is that vector which is used to specify position of a body or anything with respect to a fixed point, such as the origin of coordinate system (it means that it tells you that how far and in what direction is a point from the origin of a coordinate system)

31. Negative of a vector: - a vector whose magnitude is same but the direction is opposite.

32. Parallelogram law: - if sides of a parallelogram represents to vectors to be added, then diagonal of the parallelogram represents their resultant.

33. Resolution of vectors: - the process of splitting a vector into its two or more components.

34. Composition of vectors: - the process of joining two or more vectors to get a single resultant vector is called composition of vectors.

35. Scalar or dot product: - if multiplication of two vectors results in a scalar quantity then such type of multiplication of vectors is called scalar or dot product.

36. Vector or cross product: - if multiplication of two vectors results in a vector quantity, then such type of multiplication is called vector product. Since this type of product is represented by placing a cross between the vectors to the multiplied.

Chapter 3

Motion

(Every action has reaction! Yes exactly, if you can not please your books how you will be pleased…?)

37. Motion: - When an object changes its position with respect to its surrounding it is said to be in motion.

38. Rest: - When an object does not change its position with respect to its surrounding it is said to be at rest.

39. Translatory (or linear) motion: - A body is said to possess translatory motion when it follows straight path.


40. Rotatory (or circular/angular) motion: - When a body moves in a circle (i.e. may spin or rotate about a fixed point).

41. Oscillatory (or vibratory) motion: -when a body moves to and fro about its mean position

42. Kinematics: - It is the study of motion of objects without considering the forces acting on them

43. Statics: - The study of objects at rest

44. Dynamics: - It is the study of cause of motion.

45. Rate: - Anything divided by time.

46. Displacement: - the shortest straight distance between the two points, having a particular

direction. Or the change in position of the body.

47. Distance: - it is the length of the path (curved/line) described by an object moving in space.

48. Velocity: - the rate of change of displacement is called velocity

49. Uniform velocity: - The velocity which does not change in magnitude and direction. OR. It is the equal distance covered by a body in equal intervals of time in particular direction

50. Speed: - the magnitude of velocity is called speed. OR the rate of change of distance is called speed.

51. Acceleration: - the rate of change of velocity is called acceleration.

52. Uniform acceleration: - when the change in velocity is constant in equal intervals of time.

53. Gravity: - It is the force by virtue of which the earth attracts the bodies towards its centre.

54. Acceleration due to gravity: - It is the acceleration in free fall bodies by gravity.

55. Newton’s First Law of Motion: - it states that “A body continues its state of rest or uniform motion unless an external force acts on it”

56. Inertia: -It is the property of matter by virtue of which it opposes any change in its state of rest or that of motion.

57. Force: -It is the agency that causes or tries to change the state of rest or that of the motion of the body.

58. Newton’s second law of motion: - According to it


“When an unbalanced force acts on a body it produces acceleration in the body in the direction of force which is directly proportional to the force and indirectly proportional to mass of the body”

59. Newton’s third law of motion: - It states that “Every action has an equal and opposite reaction”60. Weight: - Weight of the body is the gravitational pull of the earth on the body.

61. Tension: -When an object is suspended by a string the force that acts along the string and is equal in magnitude and opposite in direction to the weight is called tension.

62. Thrust: -A forcefully pushing force.

63. Up thrust: - It is the force that pushes things up in water.

64. Reaction: -The opposing force of action (which is the application of force)

65. Friction: -The resistive or opposing force to the motion of the object generated when the two surfaces or in contact.

66. Static Friction: -The friction between the body and the surface when the body is at rest

67. Kinetic or dynamic Friction: -When the body is in motion relative to the surface then the force of friction between the object and surface is of dynamic type.

68. Sliding Friction: -When a body slides on a surface the corresponding force of friction is called sliding friction.

69. Rolling Friction: -When a body rolls on a surface the corresponding force of friction is called rolling friction.

70. Limiting Friction: -The maximum static friction when the object is on the verge of slipping is called limiting friction.

71. Fluid Friction: -When a solid object moves through a fluid (viscous medium), it experience an opposing force on it, called fluid friction.

72. Resistance: -the force that prevents the motion.

73. Frame of Reference: -A set of coordinate axes in terms of which the position or movement may be specified or with reference to which physical phenomenon may be stated mathematically.

74. Internal frame of reference: -A frame of reference which is at rest or moves with constant velocity and the acceleration in it is zero, also it allows the Newton’s law to be applicable it.

75. Non inertial frame of reference: - Such a frame of reference is accelerated.76. Momentum: - It is defined as the product of mass and velocity of the body.


77. Law of conservation of momentum: -The total momentum of an isolated system before and after collision remains conserved.

78. Impulse: -The change in momentum that takes place when a large force acts for a short interval of time.

79. Elastic collision: - The collision after which both the momentum and kinetic energies are conserved.

80. Inelastic collision: -In such a collision momentum is conserved but the kinetic energy is altered.

Chapter 4

Motion in two dimensions

(I am the great fan of the greats for their great thoughts of the greatness and the greatest of all these greats in the greatness of my knowledge is the Prophet Muhammad (s.a.w) who taught us the greatness of Almighty Allah by his great character of the greatness.)

81. Two dimensional motion: - If a body moves in two directions simultaneously (along x or y axis or it moves in a plane). Then its motion is called two dimensional motion.

82. Projectile: - Any object that is given any initial velocity and which subsequently follows a path determined by the gravitational force acting on it and by the frictional resistance of the atmosphere is called projectile.

83. Projectile Motion: - If a body moves with a constant velocity along horizontal direction and at the same time falls freely under the action of gravity (i.e. it has constant vertical acceleration “g”), then its motion is called projectile motion.

84. Trajectory: -The path followed by a projectile under gravity is called trajectory which is parabola.

85. Angle of projection: -It is the angle made by a projectile with horizontal plane.

86. Time of flight: -It is the total time taken by a projectile to remain in air i.e. the time elapsed between the launching and landing of a projectile.

87. Maximum horizontal distance: -It is the maximum horizontal distance covered by a projectile

88. Horizontal Range: -It is the distance covered by projectile from the point of launching to the point of landing.


89. Maximum horizontal Height: - The maximum height attained by a projectile where its vertical component of velocity becomes zero.

90. Maximum Range: -It is the maximum range attained by a projectile when it is launched at an angle of 45

91. Radian: -The angular displacement is said to be one radian if length S of the arc is equal to radius r of the circular path.

92. Angular velocity: -the rate of change of angular displacement is called angular displacement.

93. Angular acceleration: -the rate of change of angular velocity is called angular acceleration.

94. Tangential velocity: -the velocity directed tangent to the circle is called tangential or linear velocity.

95. Tangential acceleration: -the acceleration produced when there is change in magnitude of the velocity during circular motion.

96. Centripetal acceleration: -it is the acceleration directed towards the centre of the rotating body and is generated when there is change in direction of the velocity.

97. Centripetal force: -the force responsible for centripetal acceleration acts along the string or rope towards the centre

.98. Time period of revolution: -the time required by a body to complete one revolution is called

its time period of revolution.

Chapter 5

Torque, Angular momentum and Equilibrium.

(The difficult work of life is to maintain equilibrium in life by hard work in life)

99. Torque: - the turning effect of force is called torque OR the cross product of position vector and the force applied.

100. Moment of a couple: -couple is a pair of forces with equal magnitude and opposite direction, with lines of action that are parallel but don not coincides.

101. Centre of mass: -it is the point on object where the entire mass of the body is concentrated.


102. Centre of gravity: -it is the point where the net gravitational force acts. OR That point in a body or system around which its mass or weight is evenly distributed or balanced and through which the gravity acts.

103. Equilibrium: -a body at rest or with uniform motion is said to be in equilibrium.

104. Static equilibrium: -when a body is at rest it is said to be in static equilibrium.

105. Dynamic equilibrium: -a body moving with uniform motion constitutes dynamic equilibrium.

106. Translational equilibrium: -when a body moves constant linear velocity it results in translational equilibrium.

107. Rotational equilibrium: -a type of equilibrium in which body rotates in a circle with uniform angular velocity.

108. first condition of equilibrium: -according to it “a body will be in equilibrium if the sum of all the forces acting on it is zero”

109. second condition of equilibrium: - according to second condition of equilibrium “the body will be in equilibrium if the sum of all the torques acting on the system or body is zero”

110. Angular momentum: -angular momentum may be defined as the cross product of position vector and linear momentum. i.e. L = r ×p

Chapter 6GRAVITATION

(The planet earth is not perpetual to provide houses to keep alive to you it digs graves for you too because the same farmer who sows, reaps too; the same Almighty Allah who sprouts life determines death too not to perish you but to put perpetual life of heaven or hell in you)

111. Gravitation: - it is the natural force of attraction between the material bodies.

112. Gravitational field: - it is the around an object under which the effect of gravitation con be experienced.

113. Newton’s law of gravitation: it states that “ every body in the universe attracts every other body in the universe with a force of attraction (gravitation) that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them”

114. Density: -mass per unit volume is called density.


115. Weight: - it is a force through which the earth attracts the bodies towards its centre is called weight of the body. W=mg

116. Weightlessness: -a condition of free fall OR it is a condition in which body does not experience ( feel) the gravitational effect

.117. Artificial gravity: -a simulated gravity established in space by technological means such

as spinning of the satellite etc.

Chapter 7

WORK, POWER AND ENERGY

(If your small brain can dream big to understand Physics, then why can you big body not do small work to let it come true…?)

118. Work: -work is said to be done on a body if it attains some displacement with the application of force. OR it is the dot product of the applied force and the displacement covered.

119. Conservative field: -A field is said to be conservative if work done is independent of the path followed and the net work done in a closed path is zero.

120. Power: -the rate of doing work is called power. OR work done per unit time. 121. Energy: -the ability or capacity to do work is called energy.

122. Kinetic energy: -the energy possessed by a body when it is in motion is called kinetic energy

.123. Potential energy: - the energy possessed by a body when it is at rest or hanged or due its

position is called potential energy.

124. law of conservation of energy: it states that “ the energy can neither be created nor destroyed”

125. Wind: -the moving air is called wind.

126. Solar energy: -the energy of the sun light is called solar energy.

127. Fossils: - the remains of the organism of the past that owing to some devastations got buried.


Chapter 8

WAVE MOTION AND SOUND

(WAVES ALREADY EXISTED, WE ONLY DISCOVERED THEM AND SUBSEQUENTLY GOT MOBILES; THE GOODNESS IS ALREADY EXISTED IN PEOPLE WE ONLY NEED TO DISCOVER IT TO GET LOVING LIVES)

128. Vibrational motion: -when a body moves to and fro about its mean position it is said to be in vibrational or oscillatory motion

129. Periodic motion: -that motion that repeats by itself is called periodic motion.

130. Vibration: -one complete round trip of a body about its mean position is called vibration.

131. Frequency: -the number of vibrations (or revolutions) per unit time is called frequency. 132. Amplitude: -it is the maximum displacement of a vibrating body from the mean position.133. simple harmonic motion: it is characterized by;

I. its motion is vibratoryII. acceleration of the body is directly proportional to the displacement about a fixed point at

the middle(mean position)III. The motion of the body is always directed towards the mean position.

134. Simple pendulum: -a simple ideal pendulum consists of a point mass suspended with the help of a weightless, inextensible and flexible string whose other end is attached with the rigid body.

135. Time period: -time taken by a body to complete one vibration is called its time period of vibration.

136. Natural time period: -the time period with witch a body vibrates in the absence of external forces.

137. Natural frequency: -the frequency at which a system vibrates freely without being disturbed by an external force.

138. Second’s pendulum: -it is the pendulum whose time period is two seconds.

139. Resonance: - when natural frequency of a body capable of vibrating matches with the frequency of an external periodic force then the body starts vibrating with the increased amplitudes. The phenomenon is called resonance.

140. Wave: - A wave is a traveling disturbance. OR a wave is a mechanism through witch energy or disturbance travels from one place to the other.


141. Mechanical wave: - The wave that requires a material medium (solid, liquid or gas) for its propagation is called mechanical wave.

142. Electromagnetic wave: - the waves that don not require material medium for their propagation are called electromagnetic waves.

143. Transverse waves: - the waves whose vibrations are perpendicular to the direction of the propagation of the waves.

144. Longitudinal or compressional waves: - a wave in witch vibrations are parallel to the direction in which a wave is traveling, is called longitudinal (or compressional) wave.

145. Frequency of waves: -the number of waves passing through a point in one second is called frequency of waves.

146. Wave length: -it is the distance between two consecutive (side by side ) crests or troughs. But in case of longitudinal waves it is distance between two successive compressions or rarefactions.

147. Sound: - sound is a form of energy that produces the sense of hearing. OR sound is a form of energy that produces sense of hearing in our auditory system.

148. Audible sound: -the sound that can be heard and it is of the frequency ranging between 20 Hz to 20,000 Hz.

149. Infrasonic waves: -sound waves of frequency less than 20 Hz are called infrasonic waves.

150. Ultrasonic waves: -The sound waves whose frequency is greater than 20,000 Hz are called ultrasonic waves.

151. Music: -the sound that produces pleasant effect in our auditory system is called music.

152. Noise: - the sound that has a random, jarring or disagreeable impact on our auditory system.

153. Intensity of sound: -the amount of sound energy passing perpendicularly through the unit area of a surface in one second is called intensity of the sound.

154. Loudness: -the magnitude of sound produced in our auditory system is called loudness OR the attribute of sound that determines the magnitude of the auditory sensation produced and that primarily depends upon the amplitude of the sound waves involved.

155. Weber-fechner law: according to it: “the loudness of sound is directly proportional to the log of intensity of the sound.

156. Intensity level: -the difference in the loudness of a given sound and the faintest sound is called intensity level

.


157. Faintest sound: -the threshold sound before below it we can not hear.

158. Pitch of sound: -pith is that characteristics of sound with the help of witch a shrill sound can be distinguished from a grave one.

159. Quality: -quality of sound is characteristics of sound with helps distinguishing the sound having same pitch and frequency.

160. Beats: - To strike repeatedly. OR The pulsation resulting from a combination of two waves of slightly different frequency

161. Adiabatic process: - the thermodynamic process involving no loss or gain of energy in the system or particular region.

162. Isothermal process: -the thermodynamic process during which the temperature of the system remains constant is called isothermal process.

163. Doppler’s effect: -the apparent change in pitch of the sound due to the relative motion of the source and listener is called Doppler’s effect.

164. Sonic boom: -an explosive sound caused by the shock waves preceding an aircraft traveling at or above the speed of the sound.

165. principle of superposition of waves: - according to it: “when particles of a medium are disturbed simultaneously by two or more waves then their net displacement from their mean position will be equal to the algebraic sum of the individual displacements due to individual displacements”

166. Standing or stationary waves: - standing wave also called stationary wave is the combination of two waves moving in opposite direction, each with same amplitude and energy and is generated when the string is confined at both the sides and then vibrated.

167. Antinodes: -the points where the vibrating displacement is maximum from the centre.

168. Node: -the points of zero amplitude are called nodes.

169. fundamental frequency: - also called first harmonic is the lowest tone of harmonic series

170. overtone: -if the string tuned properly such that two loops are formed then the frequency f2

with which now it vibrates first overtone or second harmonic

171. Sonometer: - standing waves generating device.

172. Loop: -the more or less circular figure that curves back to cross itself.


Chapter 9

THE NATURE OF LIGHT

(Constructive interference i.e. the brightness results when the uniting waves are in phase but it leads it destructive interference when they are out of phase, so stay united to make happier life days by these ways)

173. LIGHT: - THE NATURAL AGENT THAT STIMULATES SIGHT AND MAKES THINGS VISIBLE.

174. Interference of waves: -if two exactly similar waves superpose each other (i.e. pass through the same region of space simultaneously) then at some points they reinforce (i.e. they help each other and their effect enhances) while at other points they cancel each other’s effect (i.e. their net effect decreases. This phenomenon is known as interference of light.

175. Phase coherence: -if the waves produced simultaneously are alike, they are said to be in phase coherence.

176. Constructive interference: -constructive interference takes place when the waves reinforce each other.

177. Destructive interference: - it is brought about when the waves cancel each other’s effect.

178. Path difference: -it is the distance covered by waves measured from source to the given point.

179. Fringe spacing: -it is the distance between two consecutive bright or dark fringes.

180. Phase reversal: - when a wave traveling in a rare medium (medium of lower refractive index) reflects from a denser medium of high refractive index, then its crest before reflection becomes trough after reflection.

181. Newton’s rings: - if a beam of monochromatic light is allowed to fall on a Plano-convex lens placed on a plane glass plate then alternate bright and dark rings are produced. These rings are known as Newton’s rings.

182. Diffraction:-the bending of light around the edges of an object. OR The breaking up of a ray of light bands or into the colors of the spectrum, caused by the interference of one part of beam with another, as when the ray is deflected at the edge of an opaque object or passes through a narrow slit.

183. Frensel diffraction: in Frensel diffraction the source and the screen are finite and the diffracted rays are not parallel.


184. Frawnhoffer diffraction: -in Frawnhoffer diffraction the point source of light and the screen on witch the diffraction is to be produced are at infinite distance so that the diffracted rays become parallel.

185. Diffraction grating: - a plate of glass or metal ruled with very close parallel lines, producing spectrum by interference or diffraction of light.

186. Grating element: -let a be the width of a slit and b be the width of an opaque then a + b is called grating element.

187. Path difference: -the difference in the optical paths of two light rays having common initial and final points. OR An X-ray beam is reflected from the upper plane and the second x-ray is reflected from the lower plane these two beams will cover different distances before entering the eye (second beam will cover longer distance) difference in distance covered is called path difference.

188. Wave fronts: - the geometrical pattern (or locus of all points), having same state of vibration is known as wave front.

189. Polarization of light: -the phenomenon of confining the vibrations of electric vectors in only one plane, ultimately leading to the proof of light waves as transverse.

Chapter 10

Geometrical Optics

(People are bad enough to tease you but I am sure you are good enough to forgive them)

190. Optics: -the scientific study of light and vision, chiefly the generation, propagation and detection of electromagnetic radiation, having wavelength greater than that of x-ray and smaller than that of microwaves.

191. Reflection: - the bouncing back of light into the same medium is called reflection.

192. laws of reflection: I. Angle of incidence is always equal to the angle of reflection.

II. Incident ray, refracted ray and the normal to the reflecting surface, all are in one plane.

193. regular reflection: - in such reflection the incident and the reflected rays both are parallel

194. Diffused or irregular reflection: -if the incident and the reflected both the rays are not parallel to each other they are said to form diffused or irregular reflection.


195. Mirror: - the reflecting surfaces are called mirrors.

196. Lens: -the refracting objects are known as lenses.

197. Real image: -an image that can be projected at screen, is inverted and formed by the actual intersection of the reflected or refracted rays.

198. Virtual image: -An image that can not be projected at screen, is erect and formed by the diverging reflected or refracted rays when they are produced backward.

199. Spherical mirrors: -spherical mirror is a part of a sphere.

200. Concave mirror: - if the reflecting surface is on the inner side of the spherical mirror then it is known as a concave mirror.

201. Convex mirror: -if the reflecting surface is on the outer side of the spherical mirror then it is known as convex mirror.

202. Pole: - the mid point of a spherical mirror or lens is called pole.

203. Curvature: -the state of being curved or the degree to which some thing is curved.

204. Centre of curvature: -centre of the sphere of which the spherical mirror or lens is a part is called centre of curvature.

205. Radius of curvature: -radius of sphere of which the mirror or lens is a part is called radius of curvature.

206. Principle axis: -an imaginary straight line passing through pole and centre of curvature of a mirror or lens is called principle axis.

207. Focus of a concave mirror: -if a beam of rays parallel to principle axis is incident upon a concave mirror then after reflection from the mirror all the rays converge to one point “F”. this is called focus.

208. Focus of a convex mirror: -if a beam of rays parallel to principle axis is incident upon convex mirror then after reflection from the mirror all the rays diverge and appear to come from a point behind the mirror. The point is called focus of the convex mirror.

209. Principle focus of the convex lens: -the converging point of refracted rays from the convex lens.

210. Focal length: -the distance between focus and pole of a mirror is called its focal length.

211. Mirror equation: -mirror equation is mathematical relation between object distance p, image distance q and the focal length f of a mirror.


212. Magnification: -the ratio of image height to object height. It may also be defined as the ratio of image distance to object distance.

213. Angular magnification: -angular magnification is the ratio of visual angle subtended by an image to the visual angle subtended by the object.

214. Refraction: -the passage of light, sound, heat etc from one medium to another with the oblique change in the direction.

215. Snell’s law: according it: “the ratio of sine of angle of incidence to sine of angle of refraction for a given pair of media is always constant”

216. refractive index: - it may be defined in the following ways:I. The ratio of speed of light in medium 1 to the speed of light in medium 2

II. The ratio of incident angle to that refracted angle.III. The ratio of real depth to apparent depth.IV. Reciprocal to the sine of critical angle

217. Critical angle: -the angle of incidence for which angle of refraction is equal to 90 is called critical angle.

218. Total internal reflection: -if the angle of incidence is increased beyond the critical angle then no refraction will take place, instead light will be totally reflected back. The phenomenon is called total internal reflection.

219. Convex lens: -the converging lenses thicker at the middle and thinner at the edges are called convex lenses.

220. Concave lens: the diverging lens thinner at the middle and thicker at the edges.

221. Aperture: -the diameter of boundary of a lens is called aperture.

222. Power of a lens: -the reciprocal of focal length expressed in diopters.

223. Spherical aberration: -the failure in of refracted rays in converging at the principle focus ultimately resulting in the blurring of the image.

224. Chromatic aberration: -color distortion in an image produced by a lens, caused by the inability of the lens to bring the various colors of light to focus at a single point.

225. Microscope: -an instrument with the help of which the minute objects can be seen magnified.

226. least distance of distinct vision: -the nearest position to which the object can be seen clearly without stressing the eyes

227. Compound microscope: -it is an optical instrument used to see near objects of very small dimensions clearly, primarily consist of objective lens and eye piece.


228. Objective lens in compound microscope: -the convex lens of short focal length, nearer to object is called objective lens.

229. Eye piece (ocular lens) of compound microscope: - the convex lens of relatively larger focal, near to eye to display the image.

230. Telescope: -telescope is an optical instrument used to make distinct objects appear magnified, so that they may be seen distinctly.

231. Astronomical telescope: -it is an optical instrument that is used to view heavenly bodies (i.e. planets, stars etc.)

232. Terrestrial telescope: -it is an optical instrument used to view distinct objects on earth clearly.

233. Galilean telescope: -also called opera glass is used to view objects on earth.

234. Spectrometer: -an apparatus used for the recording and measuring spectra, especially as a method of analysis.

235. The eye: -the light sensitive vision organ.

236. Sclera: -the tough white fibrous outer envelope of tissue, covering the entire eye ball except cornea.

237. Cornea: -the transparent convex shaped front tissue, covering iris and pupil.

238. Choroids: -the pigmented vascular layer of the eyeball, lying between sclera and retina.

239. Iris: -the contractile, circular diaphragm forming the colored portion of the eye and containing a circular opening, the pupil, in its center.

240. Pupil: -the opening in the center of the iris through which light enters the eye.

241. Retina: -a layer at the back of eyeball, containing cells that are sensitive to light and that trigger nerve impulses that pass via the optic nerve to the brain.

242. Crystalline lens: -the transparent elastic structure behind the iris by which light is focused onto the retina.

243. Aqueous humour: -the clear watery fluid, circulating in the chamber of the eye between the cornea and lens.

244. Vitreous humour: -the transparent gelatinous substance, filling the eye ball behind the crystalline lens.


245. Myopia: -it is the condition of short sightedness in which nearby objects can be seen clearly.

246. Hyperopia: - an abnormal condition in which the distinct objects can be seen clearly rather than near one.

Note: Chemistry and Biology Definitions also available!

e.g.

247. Chemistry: - The scientific study of inanimate matter is called Chemistry.

248. Biology: - The scientific study of life is called biology

249. Ornithology: -The scientific study of birds is called ornithology.

250. Gerontology: -The science of aging is called gerontology.

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Date post:	21-May-2015
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