* Reflection is a phenomenon of bouncing back of light when a beam of light falls on a surface. * Refraction is the bending of light when a ray of light travels from one medium to another. *Due to change of medium, the phase velocity of the wave is changed but its frequency remains constant *When a scale is immersed in a glass of water, it seems to be bended due to - refraction. *Star appears to be twinkling due to -Refraction *Optical illusion which is observed usually in deserts and highways on hot summerdays -Mirage *The phenomenon of mirage in deserts is due to - Refraction *Fata Morgana is a term associated with -Mirage *Snell’s law is related with Refraction. *The tank appears shallow than its actual depth due to- Refraction *Device which works by the principle of reflection and refraction Ans : Periscope *The measure of optical density of the medium is Refractive index Refractive index of a medium = Speedof light in vacuum/ Speed of light in medium
*The total internal reflection principle finds its ( application in the construction of optical fibres, endoscopy, vehicle reflectors, binoculars etc. *A diamond sparkles due to total internal reflection because it has a high refractive index. *Working principle of Optical fibre Ans : Total Internal reflection *Indian physicist who invented optical fibre Ans : Narinder Singh Kapany *Working principle of automotive rain sensors Ans : Total Internal Reflection *Optical fibres are light pipes which carries optical energy from one part to another without any loss in energy.
*The splitting of composite, beam of light into its constituent colours is called Ans : dispersion of light. *It was discovered by Ans : Sir Isaac Newton. *Device used for the splitting of composite beam of white light into its constituent colours Ans : Prism *Rainbow is caused by Total Internal reflection, refraction and dispersion of light by the water particles present in the atmosphere. *The red colour in rainbow is seen at an angle of 42.8° and that of violet is at 40.8°. *Colour at the centre of rainbow - Green *When we look from the outer space rainbow is seen as a circle. But when we look from the earth, rainbow is seen as semicircle.
* The distribution of light energy when two or more lightwaves superimpose to each other is called interference. *The different colours in soap bubbles is due to Interference of light. *Colours that appear on the upper layer of oil spread on road is due to Ans : Interference. * Holography is a technique of recording and reproducing three dimensional images based on the principle, interference of light. The 3D images thus produced are called holograms. * Interference pattern using light waves was first observed by a British Physicist, Thomas Young.
*When light passes through a very small object (ie, sharp edge, slit, wire etc), it spreads out into the geometrical shadow of the obstacle. This process is known as diffraction of light. *The projector in a film theatre works on the principle Ans : Diffraction. * Rings around the sun is due to Ans : Diffraction *The optical phenomenon which causes fringe pattern of CD is Ans : diffraction
Scattering of light
*The blue colour of the sky is due to -Scattering *Reddening of sun at sunrise and sunset occurs due to the scattering of light. *Light of shorter wavelength is scattered more than the light of longer wavelength. *The colour which scatters most Ans : Violet *The colour which scatters least Ans : Red *More reflection and less scattering of light occurs from most objects, leads to brighter appearance of coloured bodies. *The colour used in fog lamp of vehicles Ans : yellow light *In winter or rainy season light rays are scattered most. So we use yellow coloured fog lamp as the yellow colour scatters least. *For an astronaut on moon sky appears in black colour due to the absence of scattering of light as there is no atmosphere in moon. *Blue colour of the sky and yellow tone of the sun are due to Ans : Rayleigh Scattering
*The phenomenon of confining the vibrations of a transverse wave to a particular direction is called Ans : Polarisation. *A natural polarising material is Tourmaline *Nicol prism is a polaroid. *Polaroids are used in windows of aeroplanes and cars, sun glasses, three dimensional motion pictures, oil paintings to improve the colour contrast.
*Apparent change in frequency of a light or a sound wave when the source or the observer moves with respect to one another is called Ans : Doppler Effect *Red shift and blue shift occur due to - Doppler effect of light. *Increase in frequency (decrease in wave length) of the visible light when it moves towards the observer is called Ans : Blue shift *Decrease in frquency (increase in wave length) of the visible light when it moves away from the observer is called Ans : Red shift *High pitch of the siren of an approaching ambulance which passes an observer is due to Ans : Doppler effect *Law associated with polarisation of light Ans : Brewster's Law
*Scattering of light by the particles in a colloid is known as Ans : Tyndal effect (Tyndal Scattering) *Sunlight passing through a mist is an example of Tyndal effect. *A blue colour is sometimes seen In the smoke emitted by motor cycles is due to Ans : Tyndal effect
*A lens is a transparent medium bounded by two surfaces atleast one of which is a curved surface. *Convex lens (Converging lens) is thicker at the centre and narrower at the edges. *It is used in optical instruments, such as microscope, telescope etc for magnifying images. *The lens in human eye Ans : convex lens. *Image formed in convex lens Ans : Real and inverted *Concave lens (diverging lens) is narrower at the centre and thicker at the edges. *Image formed in concave lens Ans : Virtual and erect * Type of image formed by diverging lens -small, virtual image *Lens is not used in pinhole camera. *The ability of an optical instrument to produce separate images of two objects clearly is called Ans : Resolving Power *Focal length and power of a concave lens is always negative. *Focal length and power of a convex lens is always positive. *When a convex lens is placed in water its focal length Ans : Increases *Power of a lens increases as its focal length decreases. *Power is the reciprocal of focal length P = 1/f *Persistence of vision of human eye is 1/16 seconds. *Speed of Modem movies is 24 frames per seconds. *Short sight can be rectified by using Ans : Concave lens *Long sight can be rectified by using Ans : Convex lens
*A concave mirror form a virtual or real image depending on the position of object. *Concave mirror is also used by dentists and ENT doctors. *The image obtained from a light ray that do not actually come from the point of source is called virtual image *A real image is formed by the actual intersection of rays. *The reflector behind a spot lamp or car head lamp is parabolic. *In plane mirror the size of the object and image are same. *The shortest height of a plane mirror required to view the full size image of a person of height ‘L’ cm is L/2 cm. * Ratio of the height of the image to the height of the real object is known as Ans : Magnification *Mirror equation 1/u 1/V = 1/f *If a person is reflected in a plane mirror, his right hand side appears to be the left hand side of the image. This phenomenon is known as - lateral inversion. The image is known as mirror image.
Nobel prizesi in Physics
*1901- Whilhelm Rontgen *1903 - Henri Becquerel, Pierre Curie, Marry Curie *1904 - Lord Rayleigh *1906 - JJ.Thomson *1909 - Marconi, Karl Braun *1913 - Kamerlingh Onnes *1915 - William Henry Bragg and William Lawrence Bragg *1918 - Max Planck *1922 - Niels Bohr *1930 - C.V. Raman *1967 - Hans Bethe *1969 - Murray Gell-Man *1983 - Subrahmanyan Chandrasekhar, William Fowler *2001 - Eric Cornell, Carl Wieman,Wolfgang Ketterle *2013 - Francois Englert, Peter Higgs *2014 - Isamu Akasaki, Hiroshi Amano, Shuji Nakamura *2015 - Arthur B. Me Donald, Takkaki Kajita *2016 - J. Mochael Kosterlitz,Duncan Haldane,David J. Thouless
*Convex lens is also known as Ans : Converging lens *Concave lens is also known as Ans : Diverging lens *The lens in Human Eye Ans : Convex Lens *Image formed in Convex lens Ans : Real and inverted *Image formed in Concave lens Ans : Virtual and erect *Lens used as magnifying glass Ans : Convex Lens *Lens used in Microscope and Telescope Ans : Convex Lens *Power of a lens is measured in Ans : Dioptre *Mirror used in solar cooker Ans : Concave Mirror *Mirror used as rearview mirrors in vehicles Ans : Convex Mirror *Lens used in car head light Ans : Concave Lens * Mirror used by the doctors for examining teeth, eyes, ear, nose etc Ans : Concave Mirror *Mirrors used as shaving mirrors Ans : Concave mirror *Short sight and long sight can be corrected together by Ans : Bifocal Lens *Bifocal Lens was invented by Ans : Benjamin Franklin
*Lowest atmospheric layer Ans : Troposphere *Most clouds and weather are found in Troposphere *Weather change occurs in Ans : Troposphere *Troposphere is thicker at the equator and thinner at the poles *In troposphere the temperature decreases with altitude. *The line which separate Troposphere and Stratosphere Ans : Tropopause *The layer which is known as lower atmosphere Ans : Troposphere * The densest part of the atmosphere which contains 85% of atmosphere’s mass Ans : Troposphere
*The second lowest layer of Earth’s atmosphere Ans : Stratosphere *Ozone layer is found in Ans : Stratosphere *In stratosphere temperature increases with altitude. *Layer in which jet airplanes fly Ans : Stratosphere *The line which separates stratosphere and Mesosphere Ans : Stratopause
*Layer above the stratosphere Ans : Mesosphere *In stratosphere temperature decreases with increasing altitude. *The coldest part of atmosphere are located in Ans : Mesosphere *The line which separates Mesosphere and Thermosphere Ans : Mesopause
*Fourth layer from Earth surface Ans : Thermosphere *Temperature in this layer is very high. *International Space Station Orbit is found in Thermosphere *In Thermosphere temperature increases with height *Gravitational force is very less in Ans : Thermosphere *The layer which is located above Thermosphere Ans : Exosphere *Ionosphere is the part of Ans : Thermosphere *In Ionosphere air is ionized by the sun’s ultraviolet light *Radio waves are found in Ans : Ionosphere
*Ozone layer is found within the Stratosphere *Ozone layer absorbs most of the Ultraviolet (UV) radiation. *Colour of Ozone layer - Light blue *Ozone layer was discovered by Charles Fabry and Henri Busisson in 1913 *Ozone depletion is mainly due to -Chlorofluoro Carbon (CFC) *International Ozone day Ans : 16th September
*C.V. Raman discovered Raman effect in 1928 (February 28) *February 28 is observed as National Science day every year. *In 1930 C.V. Raman got Nobel prize for Physics for the discovery of Raman effect. *Raman effect is used in the study of Ans : Molecular Energy *Raman effect is associated with Ans : Scattering of Light *Collaborate of C.V. Raman who helped in the discovery of Raman effect Ans : K.S. Krishnan
* Study of Sound Ans: Acoustics *Sound waves can’t travel through Ans : Vacuum *Sound is a longitudinal wave *A medium is necessary for sound to travel Sound travels faster in Ans : Solids *Sound travels slower in Ans : Gases *Solid medium in which speed of sound is greater Ans : Steel *Hearing capacity of human-20 to 20,000 Hz Speed of sound in air Ans : 340 m/s *Speed of sound in water Ans : 1453 m/s *As the density of medium increases speed of sound Ans : Increases *As the temperature of the medium increases speed of sound Ans : Increases *Properties of sound Ans : Pitch, Loudness, Timbre (Quality) *Shrillness of sound is called as Ans : Pitch *Intensity of sound is identified by Ans : Loudness *Unit of frequency of sound Ans : Hertz (Hz) *Unit of intensity of Sound Ans : Decibel (db) *The unit which is usually used to denote the intensity of pollution Ans : Parts Per Million *Unit of measuring sound pollution Ans : Decibel *Normal sound level in decibel Ans : 60 -120db *Intensity of human sound Ans : 60-65 db *Sound causing damage to hearing Ans : above 120 db *Sound allowed in hospital areas in night Ans : about 40 db *Sound allowed in residential areas Ans : 50 db (day), 40db (night) *Organ in human beings which helps to produce sound Ans : Larynx *Sound is produced due to Ans : Vibration * When sound waves are obstructed by a hard surface it is sent back to the sound source. This phenomenon is called Ans : Reflection of Sound *Echo and Reverberation are due to Ans : Reflection of sound *The phenomenon that occurs where a vibrating system or external force drives another system to oscillate with greater amplitude at a specific preferential frequency Ans : Resonance
*Term used to denote the speed lower than the speed of sound Ans : Subsonic * Term used to denote 2 times the speed of Sound Ans : Supersonic *Term used to denote 5 times the speed of Sound Ans : Hypersonic *Sound waves produced by Elephants and Whales for Communication Ans : Infrasonic *Sound waves produced by Bat, Dolphin etc Ans : Ultrasonic *Sound waves used in Ultrasound Scanning Ans : Ultrasonic sound *Audible Sound (20 Hertz to 20,000 Hertz) Ans : Sonic sound *Sound lower than 20 Hz Ans : Infrasonic sound *Sound higher than 20,000 Hz Ans : Ultrasonic sound *Persistence of sound as a result of multiple reflection Ans : Reverberation *The phenomenon of hearing a sound by reflection from a surface or obstacle after hearing the original sound Ans : Echo *Phenomenon of sound 'which is used in stethoscope Ans : Reflection of sound *Minimum distance required for the production of Echo Ans : 17 meters *Phenomenon of sound which is applied in SONAR Ans : Echolocation *Sound waves used in SONAR Ans : Ultrasonic Sound *SONAR - Sound Navigation and Ranging *Sound phenomenon which helps Bats to detect prey and obstacles in their path in night Ans : Echolocation *Devices used to measure the depth of the sea Ans : Echo Sounder (SONAR), Fathometer *Unit of measuring the depth of the sea- Ans : Fathom * 1 Fathom = 6 feet = 1.82 metre Device used to get the picture of the objects at the bottom of the sea Ans : SONAR
Intensity of sound
*Threshold of hearing - 0 db *Breathing - 10 db *whispering - 20 db *Ticking clock - 30 db *Polite Alarm clock - 30 - 40 db *Television,Alarm clock - 75db *Vacuum cleaner - 80 db *Traffic noise - 60 - 120 db *Aircraft noise - 90 - 120 db *Thunder storm - 110 db *Shot gun - 120 db *Rocket taking off - 130 db *Jet take off - 140 db *Space Vechicle launched - 140 -170 db *Above 125 db cause damage to hearing. *Normal sound level in decibel is 60 - 120 db *About 40 db is allowed in hospital areas at night
waves & Rays
*Waves used in point to point fixed telecommunication Ans : Microwaves *Waves used in Radio and Television broadcasting Ans : Radio Waves *Electro magnetic wave which is having lowest frequency Ans : Radio Waves *Electro magnetic waves having highest wavelength Ans : Radio Waves *Rays which cause sunburn Ans : UltravioletRays *Electromagnetic rays used for detecting the adulterations in ghee Ans : Ultraviolet Rays *Rays used for identifying the counterfeit currency Ans : Ultraviolet Rays *Light rays in tube light Ans : Ultraviolet Rays *Rays used in TV remotes Ans : Infrared *Rays used in distant photography Ans : Infrared *The heat of the sunlight is due to Ans : Infrared rays *Whistle used for calling dog Ans : Galton whistle *Device used in the studies of sound Ans : Sonometer *Device used for recording sound under water Ans : Hydrophone * Father of long distance radio transmission Ans : G-Marconi
*A disturbance which propagates energy from one place to another without transport of matter Ans : Wave *A wave in which the particles of the medium vibrate in a direction perpendicular to the direction of propagation of wave Ans : Transverse *A wave in which the particles of the medium vibrate in a direction parallel to the direction of propagation of wave Ans : Longitudinal wave *The propagation of disturbances produced on one part of a medium by the vibration of its particles to all other parts Ans : Wave motion *The distance between two consecutive particles which are at the same'phase of vibration Ans : Wave length *Number of vibrations in one second Ans : Frequency *Maximum displacement of a particle from its mean position Ans : Amptitude *Waves travelling through layers of earth due to big explosions, earthquakes and volcanic explosions Ans : Seismic waves *Scientist dealing with the study of seismic waves Ans : Seismologist
*LASER- Light Amplifications by Stimulated Emission of Radiation. *LASER is a source of intense monochromatic light (only one wavelength or colour). *LASER was discovered by Theodore Maiman. *The name LASER was suggested by Gorden Gould. *LASER beams are used in the medical field to perform minute operations
* MASER - Microwave Amplification by Stimulated Emission of Radiation. * MASER was discovered by Charles H.Towns.
*RADAR is Radio Detection And Ranging. *RADAR is a device that uses radio waves to detect the position of objects such as aeroplanes, missile etc. *Radar was invented by Albert H. Taylor and Leo C. Young. *Radio signals travel at a speed of 3x10^2 m/s
*The electromagnetic spectrum has electro magnetic waves ranging from - l0^3m - 10^12m *It includes radio waves, microwaves, infrared, visible region, uv, x-rays and gamma rays. *Electromagnetic wave with 'maximum wavelength Ans : Radio waves *Waves used for communication through satellites Ans : Microwave
*Electro magnetic waves with shorter wave length Ans : X-rays *X rays were discovered by Rontgen. *It is used to study the internal atomic structure of crystals; *Hard X-rays are of higher frequencies with more penetrating power than soft x-rays. *Hard X-rays are used in radiations and the treatment of cancer as it penetrates into the body tissues. *Soft X-rays are used in the photography of internal parts such as chest and bone.
*The rays which appears to be originated from outside of the earth is called cosmic rays . *Cosmic rays were discovered by Victor Hess.
*Infrared ray was discovered by William Herschel. *Waves used in TV remotes Ans : Infrared * Waves used in distant photography Ans : infrared Rays *The heat of the sunlight is due to Ans : Infrared Rays
*Rays used for detecting the adulterations in ghee and is also used for identifying the counterfeit currency Ans : UV Rays *Ray used to disinfect equipments used for operation Ans : UV Rays *The ray that causes sunburn Ans : Ultraviolet rays
*Transfer of kinetic energy from one medium or object to another or from an energy source to a medium or object Ans : Heat *The study of materials and phenomena at low temperature Ans : Cryogenics *Heat is a form of energy that gives us the sensation of hotness or coldness. *The degree of hotness or coldness of a body is defined as temperature. *Heat is measured in the unit of Joule (J). *Calorie was the unit, formerly used to measure heat. *One calorie = 4. 2 Joules *One calorie is the amount of heat required to raise the temperature of 1 gm of water by 1°C. *As we go up the atmosphere, the temperature decreases. *A black surface absorbs more heat than any other colours. *Device used to detect heat radiation is called Ans : Thermocouple *The amount of heat required to raise the temperature of unit mass of a substance by 1°C is known as specific heat .capacity *Water has the highest specific heat. *Specific heat of water is 4185 J/KgK. *Specific heat of water at 15°C is 1 calorie per gram Celsius. *Specific heat of water is minimum at 37°C. *Element with the highest specific heat is Hydrogen. *Critical temperature is the temperature above which a gas cannot be liquified even when more pressure is exerted. *Temperature at which Ice melts (Icepoint) =0°C = 273 K = 32°F *Temperature at which water boils (Steam point) = 100°C - 373 K - 212°F *Absolute Zero =' OK =-273.15°C *Temperature which shows same measurement in Celsius and Fahrenheit scale - -40 *Temperature which shows same measurement in Farenheit and Kelvin scale = 574.25 *Fraction of volume of ice seen outside when it is immersed in water - 10.5%. *The various temperature.scales commonly used are Celsius (C ), Kelvin (K), Fahrenheit (F) and Rankine (Ra). *In Centigrade Scale, the intervals between ice point and steam point is divided into 100 equal parts. *Absolute Scale or Kelvin Scale: The pressure of a gas is reduced to zero at -273.15°C when keeping the volume constant and vice versa. *In Fahrenheit Scale, the intervals between ice point and steam point is divided into 180 equal parts. *To convert celsius into Fahrenheit Scale, F = (C*9/5)32 *To convert Fahrenheit into Celsius Scale C=(F-32)*5/9 *To convert Celcius into Kelvin Scale, K=C273.15 *To convert Kelvin into Celsius Scale C = K - 273.15
*Thermometer was invented by Ans : Galelio *Mercury thermometer was invented by Ans : Fahrenheit *Clinical Thermometer was invented by Ans : Thomas Albutt *The clinical thermometer (Medical Thermometer) is a special liquid glass thermometer used to measure human body temperature and is measured on Celsius scale in degree centigrade or degree Fahrenheit. *Range of clinical thermometer is - 35°C to 42^0C. *Normal body temperature is 36.9°C (98.4°F or 310K) *Magnetic thermometer is used to measure temperature very near to absolute zero. *Magnetic thermometer works on the basis of Curies law. *Resistance thermometer is a thermometer in which temperature is calculated from the resistance of a coil. eg: Platinum resistance thermometer *Pyrometer or Radiation thermometer is an instrument used for measuring high temperatures. *Cryometer is used to measure very low temperature.
*There are three ways of heat transmission. *Heat can be transmitted in 3 ways (i) Conduction (ii) Convection (iii) Radiation *Process of exchange of hotter particles to the neighbouring colder particles is known as Ans : Conduction *Transfer of heat in a fluid with the help of heated particles from a hotter region to a colder region is called Ans : Convection *Sea and land breezes can be explained on the basis of convection. *Ocean currents, Monsoons and Trade winds are based on the principle of convection. *Transmission of heat from one point to another without heating the medium is called radiation. *The Change of vapour into liquid state is known as Ans : Condensation *Solar energy reaches earth through radiation. *The main source of our energy Ans : Sun
Thermos flask (vacuum flask)
*Thermos flask was invented by - Sir James Dewar *Vacuum flask works with the help of a vacuum between “2- glass containers which will prevent the heat loss. *Vacuum prevents heat loss by conduction and convection. *The polished shining surface inside and outside of vaccum prevents heat loss by radiation. *Thermosflask usually holds the contents below the boiling-point Of water. *Glass used to make thermos flask -Borosilicate glass. *Almost every liquid expands with the increase in temperature. But when the temperature of water is increased from 0°C to 4°C the volume decreases. If the temperature is increased above 4°C the volume starts increasing. This is called anomalous expansion of water. *The temperature at which water has least volume and high density = 4^0C Density = Mass/Volume *When water is heated from CPC to 10°C its volume decreases first and then increases. *Water expands on freezing. During the winter season water pipes, break in cold regions due to this reason. *When water filled in a bottle is allowed to freeze, the bottle breaks.
*Tendency of matter to change in volume in response to change in temperature is called as Ans : Thermal Expansion *Mercury Thermometer works on' the principle of Ans : Thermal Expansion *All substances expand on heating. *Gases expand most when heated. *Solids have the least expansion on heating. *Liquid expand more than solid on heating *Rail Road tracks are constructed in such a way that they can safely expand on a hot day without derailing when the train is travelling over them. * When the temperature increases the length of the electric lin e between 2 towers increases and line sags.
*The property of a material to conduct heat is called as - Thermal Conductivity. *Thermal conductivity of a material depends on temperature. *Unit (SI) of thermal conductivity. - watts per ... meter kelvin (W/mk) *The law of heat conduction is called -Fourier’s law. *Coefficient of thermal conductivity is. also known as - K factor or thermal admittance. *Newton’s Law of Cooling : This law states that the rate at which a hot body loses heat is directly proportional to the difference between its temperature and the ‘Surrounding temperature. *If hot water and fresh tap water are kept in a refrigerator, the rate of cooling of hot water will be faster than the tap water. * In a refrigerator cooling is produced by the evaporation of a volatile liquid, Freon inside a copper coil which surrounds the freezer. *The amount of water vapour present in air is called humidity. *Perspiration is maximum, when temperature is high and air is humid. *The exerted pressure reduces the melting point of ice. This phenomenon is known as regelation. *Skating on ice is possible due to the phenomenon of regelation. *Joule’s law is related to the heat. *Joule’s law of heating states that the heat produced in a conductor is directly proportional to the square of current (I) flowing through the conductor; resistance ® of the conductor and time (t) for which the current is passed. H = I^2 Rt *Mica is a good conductor of heat even though it is a bad conductor of electricity. *The density of a body decreases with rise in temperature. *According to the Principle of Calorimetry, heat lost by the hot body is equal to the heat gained by the cold body at thermal equilibrium.
Melting point and Boiling point
*The fixed temperature at which solid becomes a liquid at standard atmospheric pressure is called Ans : Melting Point. *Melting point of ice can be raised by the decrease of pressure: *The fixed temperature at which a liquid boils and changes itself into vapour at standard atmospheric pressure is called Ans : boiling point. *The boiling point of water increases with increase in pressure. *Water inside a Pressure Cooker boils at a temperature of 120° C as the boiling point of water increases with increase in pressure. *Melting point of Mercury is - 39^0C *Melting point of Alcohol is - 114^0C
Evaporation and Sublimation
*The process of conversion of a liquid into vapour at any temperature is known as Ans : Evaporation. *Rate of evaporation increases with increase in temperature, surface area and decrease in pressure. *Evaporation produces cooling of liquid. This is why we feel cool under fan while sweating. *The process of conversion of a solid directly into vapour when heated is called Ans : sublimation, eg: Camphor *The quantity of heat required to convert unit mass of solid at its melting point into liquid is called Ans : Latent Heat of Fusion . *For ice at CPC, the latent heat of fusion is 80K cal/kg(kilo calorie / kilogram) *The quantity of heat required to convert unit mass of a liquid at its boiling point to vapour is called Ans : Latent Heat of Vapourisation. *For water at 100°C, the latent heat of vapourisation is 540kcal/kg. *Scalding with steam is more severe than that caused by boiling water because of latent heat of vapourisation. *Heat engine is a device which converts heat energy into mechanical energy.
*A body is said to be a perfectly blackbody if its absorption power is *A Surface which absorbs all the heat radiations (ie radiations of all the wave length) incident on it is known as a - perfectly black body. *A black body is a good absorber and a good emitter of heat. *The radiation received from the sun is similar to that of a perfectly black body. *The device used to measure the temperature of sun - Pyroheliometer *Radiations emitted from a black body is called black body radiation. *Heat radiation emitted from sunlight is mainly - due to infrared rays. *The value of solar constant is - 1.34 *10^3 W/m^2 * The estimated value of surface temperature of sun is 5778K. *Black surface is good radiator as well as a good absorber of heat. So black cloths are preferred in winter. *White cloths are preferred in summer, as these absorb less heiat from the surroundings. *Study of high temperature is known as Pyrology.
*Study of motion of objects - Mechanics *The study of causes and changes in motion - Dynamics. *Motion, is the change in position of an object with respect to time and its surroundings. *A body is said to be in a state of rest if its position does not change with respect to its surroundings. This motionless state is said to be stationary. *Distance covered by a body is the actual length of path travelled by a body. *The distance travelled by a body in unit time is Speed. Speed = Distance/Time Velocity = Displacement / Time Acceleration = Change in Velocity / Time *The change in position of an object in a particular direction is called Displacement. *The distance travelled by an object in a definite direction in unit time Velocity *The rate of change of velocity of a moving body is called Ans : Acceleration *Slope of velocity time graph gives Ans : Acceleration *The shape of acceleration versus mass graph for constant force is Ans : Hyperbola *At terminal velocity the acceleration of body is zero *If the velocity of a moving body decreases, then the change in velocity in unit time is called retardation or deceleration *The motion restricted to a straight line is called one dimensional (Id) motion, eg: car moving on a straight road, throwing a stone straight up. *The motion restricted to a plane is called two dimensional (2d) motion, eg: Projectile motion, a satellite revolving uniformly around the earth, a boat moving on a lake etc *The motion in space is called three dimensional (3d) motion, eg: Motion of a charged particle, a kite flying in the air etc. *If a body is moving in a circular path, then its motion is said to be in Circular motion. Eg: The motion of earth around the sun *To-and-fro motion of an object is called Oscillatory motion. eg: Pendulum of a clock *The motion of a body in a straight line is known as Translational motion or Linear motion. eg: The motion of a car on a road. *The translational motion in a straight line - Rectilinear motion eg:- The up and down movement of lifts.
Theory of Relativity
*Theory of relativity (1905) was introduced by Ans : Albert Einstein *Theory of relativity have two separate theories (i)Special theory of relativity (a)Speed of light is constant for all observers (b)Observer moving at constant speeds should be subject to the same physical laws. (ii)General theory of Relativity (1915) *The translational motion along the curved path - Curvilinear motion eg:- The motion of a rocket in space. *The motion which repeats after regular intervals of time - Periodic motion eg:- The rotation of the earth around the sun.
Rotation and Revolution
* If the axis of the rotating body is within the body, its motion is said to be Spin motion or Rotational motion. eg: The earth spins on its own axis in 24 hrs.This will make a day. *When an object travels around another object it is known as Revolution eg: Earth revolves around the sun in 365 days.This will make an year.
*The motion of an object in a vertical plane under the influence of gravitational force is known as projectile motion. eg: Rocket fired into space, a golf ball in flight etc. *The projectile path is known as trajectory. *The path of the projectile is always a parabola. *A projectile reaches its maximum range, when the angle of projection is at 45°.
*The tendency of a body to continue its state of rest or uniform motion along a straight line is called Ans : Inertia *Law of inertia was discovered by Ans : Galileo *There are 3 types of Inertia Ans : Inertia of Rest, Inertia of Motion,
Inertia of Direction.
*As the bus starts moving, a man sitting inside leans backwards because of inertia of rest. *When a train stops suddenly, passengers in the running train feel an instant bend in the forward direction because of inertia of motion. *An athlete runs some distance before taking a long jump, by running the athlete gives himself larger inertia of motion. *The rotating wheels of an automobile throw out mud tangentially outward because of inertia of direction. *Force required to stop a moving body depends on its mass and velocity.
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