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Units and Measunements Chapter al. @® units Measurement of any physical quantity involves compoxison with certain basic onbitrarily chosen internationally accepted references called units. Classification SS, @ MEASUREMENT OF LENGTH + 1° = 1.745 x 107 nod © A= 4.85 x 10 nad Measurement of very small distances like size of molecule uses, + Optical microscope Fundamental Units Derived Units Independent of Expressed as combinations each other. of fundamental units. + Electronic microscope + Tunneling microscope + A complete set of base and denived units is called a system of units * Old systems of units: CGS, FPS and MKS. + In CGS, fundamental units axe centimeten, gram and second. In FPS, fundamental units axe foot, pound and second. In MKS, fundamental units one meten, kilogram and second. + LAU = 1.496% t0''m shy = 9.46 x 10" m +L pansec = 3.08 x 10" m + Size of proton = 10° m + Radius of Earth = 407 m Distance to boundeny of obsenvable univesse = 107° m © MEASUREMENT OF TIME Atomic. standard of time : This is based on cesium clock. Uncertainty gained oven time (4) MEASUREMENT OF MASS © SL unit : kilogram (kg) * Unified atomic mass unit (u) is used to measure masses of Etre endl Sableealasl by cesium atomic clock is less than 4 pant in 10° (loss. of about 3 ps in one year) 4 dus zm of one: C-12 atom. + tus 166x107" kg particle Electron mass * 10°" kg + Travel time for light from = 10" kg 8 = 10's + Earth mass nearest stan Obsenvable univexse 55 10° ke 10K |e Age ef universe © 101s © Accuracy AND PRECISION + Every measurement contains some uncertainty called exon. + Accuracy is a measure of has cise the menswed value is to the fue value. * Precision tells us to what resolution the quantity is measured. + Th is not wecessany that more precise value fé mare accurate. @) ST SYSTEM OF UNITS (INTERNATIONAL SYSTEM OF UNTTS) + Presently accepted internationally for measurement is SE system of units, nevised in 2018. « It is a decimal System ; hence, conversion within system is easy and convenient. + Tt has # base units and 2 supplementary units. 0) ERRORS IN MEASUREMENT Errors ER Systematic Random i aor oe Instrumental Experimental Personal Base Units Supplementary Units + Every measurement is approximate due to errors. NN. tite t ml sh ii SN] Quantity | Unit [Symbol] [SN] Quantity | Unit [Symbol |. Random errors occur inregulanly. 1. | Length meter | m Plane angle | radian | rad F + Least count error is smallest value that can be measuned by 2. | Mass kilogram | kg 2. [Solid angle | stevadian| sr instrument (occuxs within both systematic and nandom exrors). 3. [Time second Ela f + Absolute error = = 11 ~ Smear 4, | Electric current | ampere | A n : r ds 5. | Thermodynamic | ue | y «+ Relative exror = A@mean temperature mean + Poreentage ervor = A2neen 400 6. | Amount of substance! mole | mol Omean 7. | Luminous indersity | candela | ed Combination of exrors Sum or Difference Product or Quotient Az = AA + AB Sl a Ate AX AA AB Ac tf xX = a. ae” AB ac K fx = TE then F a(S) +4($) +<(#) = eradian oe i Hering +o(e B)+e(* Z) 
