December 6, 2009

Important Scientific laws - for Competitive Exams

Archimedes' Principle: It states that a body, when immersed in a liquid, experiences an upward thrust equal to the weight of the liquid displaced by it.

Avogadro's Hypothesis: It is a modification of Berzelius' hypothesis. It states that equal volumes of all gases under similar conditions of temperature and pressure contain equal number of molecules. Avogadro's law is applicable only to gases.

Boyle's Law: states that the volume of certain gas is inversely proportional to the pressure at a constant temperature. In other words the product of pressure  and volume remains constant provided the temperature is kept constant i.e., P x V = a constant if T remains the same.

Charles's Law: It states that at constant pressure all gases expand by 1/273 of their volume at 0°C for a rise in temperature of 1°C  i.e., the volume of a given mass of gas at constant pressure is directly proportional to the absolute temperature.

Dulong and Petit's Law: states that the product of atomic weight and specific heat of solid elements is nearly equal to 6.4 i.e., At wt. x sp. heat = 6.4 approx.

Gay-Lussac's Law of combining volumes: Gases react together in volumes which bear simple whole number ratios to one another and also to the volumes of the products, if gaseous—all the volumes being measured under similar conditions of temperature and pressure.

Graham's Law of Diffusion: states that the rates of diffusion of gases are inversely proportional to the square roots of their densities under similar conditions of temperature and pressure.

Kepler's Law: According to this law, a line drawn from the sun to a planet, moving around it, sweeps over a fixed area in a given interval of time.

Law of definite proportions: A chemical compound is always found to be made up of the same elements combined together in the same ratio by weight.

Law of Floatation: for a body to float, the following conditions must be fulfilled: (1) The weight of the body should be equal to the weight of the water displaced. (2) The centre of gravity of the body and that of the liquid displaced should be in the same straight line.

Lenz's Law: When there is change in the magnetic flux linked with a circuit, the electric current induced in the circuit will have a magnetic field opposing the change producing it.

Newton's Law of Universal Gravitation: states that "Every portion of matter attracts or tends to approach every other portion of matter in the universe with a force proportional to the masses and inversely as the square of the distance."

Newton's First Law of Motion: "A body continues in its state of rest or of uniform motion in a straight line unless compelled by an external force to change that state."

Newton's Second Law of Motion: "The rate of change of momentum is proportional to the impressed force and takes place in the direction of the force."

Newton's Third Law of Motion: "To every action, there is an equal and opposite reaction."
Newton's Law of Cooling: states that the rate of loss of heat of a hot body is directly proportional to the difference of temperature between the body and the surroundings and is independent of the nature of the body.

Ohm's Law: states that the ratio of the potential difference between the ends of a conductor and the current flowing in the conductor is constant, e.g., for a potential difference of E volts and a current I amperes, the resistance R,  in ohms is equal to E/I.

Principle of conservation of energy: It states that, in any system, energy cannot be created or destroyed; the sum of mass and energy remains constant.

Snell's Law: It states that the ratio of the sine of angle of incidence to the sine of the angle of refraction remains constant for any two given media.

Specific heat of substance: The quantity of heat required to raise the temperature of 1 gram.  of a substance through 1°C.


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