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# Nature of the physical world and measurement

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MEASUREMENT, PHYSICAL MEASUREMENT, CONVERSION OF FOUND OFF, FLOATING POINT MEASUREMENT, DIMENSIONS, UNITS, BASIC FORMULAE

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### Nature of the physical world and measurement

1. 1. Nature Of The Physical WorldAnd Measurement
2. 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. 3. Length t Mass Time Electric current Fundamental Quantity Temperature Luminous IntensityPhysical Quantity Amount of substance Plane angle Solid angle Derived Quantity Area, Volume, Density
4. 4. S.NO POWER PREFIX ABBREVIATION OF TEN 1 10-15 Femto f 2 10-12 Pico pExpressin 3 4 10-9 10-6 Nano Micro n μg Larger 5 10-3 Milli mAnd 6 7 10-2 10-1 Centi Deci c dSmaller 8 101 Deca daPhysical 9 10 102 103 Hecto Kilo h kQuantities 11 106 Mege M 12 109 Giga G 13 1012 Tera T 14 1015 peta P
5. 5. LIGHT YEAR AND ASTRONOMICAL UNIT 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
6. 6.  Determinationof Distance Laser pulse method Determination of mass Determinationof time Atomic clocks – 1013 sec Quartz clocks – 109 sec
7. 7. Significant figures The number of meaning digits in a number is called the number of significant figures. RULES1. All the non- zero digits in a number are significant.2. All the zeros between two non-zeros digits are significant, irrespective of the decimal point.3. The zeros at the end without a decimal point are not significant.4. The trailing zeros in a number with a decimal point are significant
8. 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. 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. 10. Rounding Off Examples 53.473 kg – 53.6 kg 0.575 m – 0.58 m 0.495 – 0.50
11. 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 a. Improper setting of the instrument. b. Wrong recording of the observation. c. Not taking into account sources of error and precautions. d. 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. 12. Dimensional AnalysisDimensions of a physical quantity are the powers to which thefundamental quantities must be raised. Fundamental Quantity Dimension Length L Mass M Time T Temperature K Electric current A Luminous intensity cd Amount of substance mol
13. 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. 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. 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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