Sunday, 6 March 2016


SI unit of Force- Newton(CGS=dyne), 1 newton= 105 dyne.
Si unit of Work- Joule(CGS=erg), 1 joule= 107 erg.
Cream separator, centrifugal drier work on the principle of the Centrifugal force.
SI unit of Power- watt.
Value of g=9.8 m/s2 decreases with height or depth from earth’s surface.
Value of g is maximum at poles.
Value of g is minimum at equator.
Value of g deceases if the angular speed of earth increases and increases if the angular speed of earth decreases.
If the angular speed of earth becomes 17 times its present value, a body on the equator becomes weightless.
Sudden fall in barometric reading is the indication of storm.
Slow fall in barometric reading is the indication of rain.
Slow rise in the barometric reading is the indication of clear weather.
Atmospheric pressure decreases with altitude, this is why it is difficult to cook on the mountain, and the fountain pen of a passenger leaks in aeroplane at height.
Escape velocity for earth= 11.2km/s, for moon= 2.4 km/s.
Pressure at a point in a liquid is proportional to the depth of the point from the free surface.
Pressure at a point in a liquid is proportional to the density of the liquid.
Hydrolic lift,  Hydrolic Press, Hydrolic brake works on the Pascal law.
Archimedes Principle: when a body immersed partly or wholly in liquid, there is an apparent loss in the weight of the body which is equal to the weight of liquid displaced by the body.
Meta Centre: when a floating body is slightly tilted from equilibrium position, the centre of buoyancy shifts. The point at which the vertical lines passing through the new position of center of buoyancy meets with the initial line is known as meta center.
Relative density is measured by Hydrometer.
The density of sea water is more than that of normal water. This explains why it is easier to swim in sea water.
When ice floats in water, its 1/10th part remain outside the water.
If ice floating in water in a vessel melts, the level of water in the vessel does not change.
Purity of milk is measured by Lactometer.
The height by which liquid ascends or descends in a capillary tube depends upon the radius of the tube.
A piece of blotting paper soaks ink because the pores of the blotting paper serve as capillary tubes.
The oil in the wick of a lamp rises due to capillary action of the threads in the wick.
The root hairs of plants draws water from the soil through the capillary action.
To prevent loss of water due to capillary action, the soil is loosened and split into pieces by the farmers.
If a capillary tube is dipped in water in an artificial satellite, water rises up to the other end of the tube because of its zero apparent weight, how long the tube may be.
Action of towel soaking up water from the body is due to capillary action of cotton in towel.
Melted wax, in a candle rises up to wick by capillary action.
If a clean and dry needle is very slowly kept on the surface of water, it floats due to surface tension.
The addition of detergent or soap decrease the surface tension of water and thus increases the cleaning ability.
Bubbles of soap solution are big because addition of soap decreases the surface tension of water.
When kerosene oil is sprinkled on water, its surface tension decreases. As a result the larva of mosquitoes floating on the surface of water die due to sinking.
Warm soup is tasty because at high temperature its surface tension is low and consequently the soup spreads on all parts of the tongue.
Viscosity is the property of liquids and gases both.
The viscosity of a liquid is due to the cohesive force between the molecules.
The viscosity of a gas is due to the diffusion of its molecules from one layer to another layer.
Viscosity of gases is much less than that of liquids. There is no viscosity in solids.
With rise in temperature, viscosity of liquids decreases and that for solids increases.
Viscosity of a fluid is measured by its coefficient of viscosity. It SI unit is decapoise or pascal second.
Venturimeter, a device used to measure rate of flow of fluid, works on Bernoulli’s theorem.
Speed of sound is maximum in solids and minimum in gases.
Unit of loudness- bel, phon, decibel.
To hear echo, the minimum distance between the observer and the reflector should be 17m.
Persistence of ear (effect of sound on ear) is 1/10sec.
If Mach number>1, body is called supersonic.
If Mach number>5, body is called hypersonic.
Bow waves: when a motor boat in a sea travels faster than sound, then wanes just like shock waves(in air) are produced on the surface of water. These waves are called bow waves.
Electromagnetic waves are transverse, hence the light is transverse wanes.
Wave nature of light explains rectilinear propagation, reflection, refraction, interference, diffraction and polarization of light.
Speed of light was 1st measured by Roemer.
Light takes 8min 19sec to reach from sun to earth.
The light reflected from moon takes 1.28 second to reach earth.
Concave mirror uses—shaving glass/ reflector for the head lights of a vehicle, search light/ in ophthalmoscope to examine eye, ear, nose/ in solar cookers.
Convex mirror uses—in rear mirror of vehicles since it provides erect images/ in sodium reflector lamp.
 Examples of total internal reflection—sparkling of diamond/ mirage and looming/ shining of air bubble in water/ shining of a smoked ball or a metal ball on which lamp soot is deposited when dipped in water/ in optical fibres.
Myopia or short sightedness—elongation of eye ball along the axis/ shortening of focal length of the eye lens/ over stretching of ciliary muscles beyond the elastic limit. Cure—Diverging lens.
Hypermetropia or long sightedness—shortening of eye ball along the axis/ increase in the focal length of eye lens/ stiffening of the ciliary muscles. Cure—Converging lens.
Presbyopia—this defect is generally found in elderly person. Due to stiffening of ciliary muscles, eye loses much of its accommodating power. As a result distant as well as nearby objects cannot be seen. Cure—Bifocal lens.
Astigmatism—this defect arises due to difference in the radius of curvature of cornea in the different planes. As a result rays from an object in one plane are brought to focus by eye in another plane. Cure—Cylindrical lens.
Kilowatt hour—it is the unit of energy and is equal to the energy consumed in the circuit at the rate of 1 kilowatt (1000 J/s) for 1 hour.
1.672 x 10-27
1.6 x 10-19
1.675 x 10-27
9.108 x 10-31
-1.6 x 10-19
J.J. Thomson
9.108 x 10-31
1.6 x 10-19
274x9.108 x 10-31

Radioactivity was discovered by Henry Becquerel, Madame Curie and Pierre Curie for which they jointly won Noble Prize.
Nucleus having protons 83 or more are unstable. They emit alpha, beta and gamma particles and become stable.
Robert Pierre and Madame Curie discovered a new radioactive element—radium.
End product of all radioactive substances after emission is lead.
Radioactivity is detected by Geiger Muller Counter.
Cloud Chamber—is used to detect the presence and kinetic energy of radioactive particles. It was discovered by C.R.T. Wilson.
Fast Breeder Reactor- a nuclear reactor which can produce more missile fuel than it consumes.

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