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 1 : Nature Of The Physical World And Measurement
 2 : Forces of Nature Sir Issac Newton, “Force is the external agency applied on a body to change its state of rest and motion” Gravitational force Electromagnetic force Strong nuclear force Weak nuclear force
 3 : t
 4 : Expressing Larger And Smaller Physical Quantities
 5 : Light Year It is the distance travelled by light in one year in vaccum. 1 Light Year = 9.467 x 1015m Astronomical unit It is the mean distance of the centre of the sun from the centre of the Earth. 1 Astronomical Unit (AU) = 1.496 X 1011m LIGHT YEAR AND ASTRONOMICAL UNIT
 6 : Determination of Distance Laser pulse method Determination of mass Determination of time Atomic clocks – 1013 sec Quartz clocks – 109 sec
 7 : Significant figures The number of meaning digits in a number is called the number of significant figures. RULES All the non- zero digits in a number are significant. All the zeros between two non-zeros digits are significant, irrespective of the decimal point. The zeros at the end without a decimal point are not significant. The trailing zeros in a number with a decimal point are significant
 8 : Significant Figures Examples 0.0631 – Three Significant Figures. 56700 - Three Significant Figures. 0.00123 – Three Significant Figures. 30.00 – Four Significant Figures. 6.320 – Four Significant Figures. 600900 – Four Significant Figures. 346.56 – Five Significant Figures 5212.0 – Five Significant Figures.
 9 : Rounding Off If the insignificant digit is more than 5, The preceding digit is raised by 1. If the insignificant digit is not more than 5, There is no change. If the insignificant digit is 5 Even there is no change. Odd The preceding digit is raised by 1.
 10 : Rounding Off Examples 53.473 kg – 53.6 kg 0.575 m – 0.58 m 0.495 – 0.50
 11 : Errors in Measurement Constant Errors It is due to faulty calibration of the scale in the measuring instrument. Systematic Errors These are errors which occur due to a certain pattern or system. Gross Errors Improper setting of the instrument. Wrong recording of the observation. Not taking into account sources of error and precautions. Usage of wrong values I the calculation. Random Errors It is very common that repeated measurement of a quantitative values which are slightly different from each other.
 12 : Dimensional Analysis Dimensions of a physical quantity are the powers to which the fundamental quantities must be raised.
 13 : Dimensional Quantities Dimensional variables are those physical quantities which possess dimensions but do not have a fixed value. Ex. Velocity, force, etc., Dimensionless Quantities There are certain quantities which do not possess dimension . Ex. Strain, angle, specific gravity, etc., Principle of homogeneity of dimensions An equation is dimensionally correct if the dimensions of the various terms on either side of the equation are the same. Ex. A+ B = C is valid only if the dimensions of A, B & C are the same.
 14 : Uses of Dimensional Analysis Convert a physical quantity from one system of units to another. Check the dimensional correctness of a given equation. Establish a relationship between different physical quantities in an equation.
 15 : Limitations of Dimensional Analysis The value of dimensionless constants cannot be determined by this method. This method cannot be applied to equations involving exponential and trigonometric functions. It cannot be applied to an equation involving more than three physical quantities. It can check only whether a physical relation is dimensionally correct or not. It cannot tell whether the relation is absolutely correct or not.
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