Chapter 1 slides na-12

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Chapter 1 slides na-12

  1. 1. 3NA Science (Physics) Chapter 1 Physical Quantities, Units and Measurement
  2. 2. By the end of the lesson, you should be able to <ul><li>Students should be able to: </li></ul><ul><li>show understanding that all physical quantities consist of a numerical magnitude and a unit </li></ul><ul><li>recall the following base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K) </li></ul><ul><li>use the following prefixes and their symbols to indicate decimal sub-multiples and multiples of the SI units: nano (n), micro (μ), milli (m), centi (c), deci (d), kilo (k), mega (M) </li></ul><ul><li>show an understanding of the orders of magnitude of the sizes of common objects ranging from a typical atom to the Earth </li></ul><ul><li>describe how to measure a variety of lengths with appropriate accuracy by means of tapes, rules, micrometers and calipers, using a vernier scale as necessary </li></ul><ul><li>describe how to measure a short interval of time including the period of a simple pendulum with appropriate accuracy using stopwatches or appropriate instruments </li></ul>
  3. 3. Physical Quantities <ul><li>A physical property is a quantity that can be measured </li></ul><ul><li>Can you name some physical quantities? </li></ul><ul><li>Length, speed, mass, weight, force, pressure, time, temperature etc. </li></ul>
  4. 4. Imagine you ask about the age of a person, and the number is a numerical value. The information conveyed during the conversation will not be very specific or useful. How old is your little sister, Jon? She is 12! 12? 12 months? 12 years old?                                                                                  
  5. 5. No NAKED numbers please!!! <ul><li>Do these numbers make sense to you? </li></ul><ul><li>What do they lack? </li></ul><ul><li>45 897.00 </li></ul><ul><li>67000 </li></ul><ul><li>0.325 3 x 10 8 </li></ul>
  6. 6. Quantities, Magnitude, Units <ul><li>The weight of a coin is 12 g . </li></ul>Physical quantity magnitude unit All physical quantities are presented with a magnitude and a unit .
  7. 7. Base Quantities and its Unit m metre length mol mole Amount of substance A ampere current s second time cd candela Luminous intensity K kelvin temperature kg kilogram mass Symbol Base unit Base quantity
  8. 8. Very small and very BIG quantities A more efficient way of expressing very big or very small number is to do so in scientific notation, using appropriate prefixes . Bacteria is very small…..it is about 0.000 001 m long… The sun is 149 342 000 000 m away from us…
  9. 9. Prefixes
  10. 10. How to convert unit?
  11. 11. Now you try! <ul><li>5500 mg = ……………… g </li></ul><ul><li>  5500 x 10 -3 = 5.5 g </li></ul><ul><li>0.45 kg = ……………....g </li></ul><ul><li>0.45 x 10 3 = 450 g </li></ul><ul><li>0.004 GB = …………… B </li></ul><ul><li>0.004 x 10 9 = 4 x 10 6 B </li></ul><ul><li>8900 nm = ……………….. m </li></ul><ul><li>8900 x 10 -9 = 8.9 x 10 -6 m </li></ul>
  12. 12. How to convert unit?
  13. 13. Your turn to try! <ul><li>250 g = ………………… kg </li></ul><ul><li>250  10 3 = 0.25 kg </li></ul><ul><li>0.000345 m = …………….  m </li></ul><ul><li>0.000345  10 -6 = 345  m </li></ul><ul><li>45 600 Hz = ……………..MHz </li></ul><ul><li>45 600  10 6 = 0.0456 MHz </li></ul><ul><li>0. 765 A = ……………. mA  </li></ul><ul><li>0.765  10 -3 = 765 A </li></ul>
  14. 14. How big? How small? <ul><li>Estimate the diameter of an atom. </li></ul><ul><li>10 -10 m </li></ul><ul><li>Estimate the diameter of the earth. </li></ul><ul><li>1.2 x 10 7 m </li></ul>
  15. 15. For accurate length measurement using ruler, the eye should be positioned in line, perpendicular to the point to be read to avoid parallax error . Measuring Length Accurately
  16. 16. Vernier Calipers <ul><li>http://members.shaw.ca/ron.blond/Vern.APPLET/index.html </li></ul><ul><li>The internal jaws can be used to measure the internal diameter of test tubes or beakers. </li></ul><ul><li>The outside jaws can be used to measure the thickness of a book or the diameter of a sphere. </li></ul><ul><li>The depth rod can be used to measure the depth of a test tube or cavity. </li></ul>
  17. 17. Main scale Vernier scale 2.1? cm 0.04 cm 2.14 cm Hence a vernier calipers can measure small length accurate to 2 decimal places in cm. How to read write down main scale reading Add vernier scale reading Using Vernier Calipers
  18. 18. Qn 1 2.15 cm
  19. 19. Qn 2 1.04 cm
  20. 20. Qn 3 3.19 cm
  21. 21. Qn 4 & 5 <ul><li>2.74 cm 4.04 cm </li></ul>
  22. 22. Micrometer Screw Gauge
  23. 23. http://www.upscale.utoronto.ca/PVB/Harrison/Micrometer/Flash/MicSimulation.html
  24. 24. How to read write down main scale (sleeve) reading Add thimble scale reading Sleeve scale Thimble scale 4.5? mm 0.12 mm 4.62 mm Hence a micrometer screwgauge can measure small length accurate to 2 decimal places in mm. Using Micrometer Screw Gauge
  25. 25. Precautions <ul><li>Never tighten the thimble too much </li></ul><ul><li>Clean the ends of the anvil and spindle before measurement </li></ul><ul><li>Check for zero error </li></ul>
  26. 26. Qn 1 7.32 mm
  27. 27. Qn 2 7.63 mm
  28. 28. Qn 3 7.00 mm
  29. 29. Qn 4 & 5 <ul><li>2.73 mm 8.57 mm </li></ul>
  30. 30. Time Measurement
  31. 31. Period of a Simple Pendulum The time taken for a pendulum to complete one oscillation is called the pendulum's period . For the pendulum on the right, one oscillation is from A to B then back to A again.
  32. 32. Factors affecting period of pendulum <ul><li>When the length of the pendulum increases , the period increases . </li></ul><ul><li>The period is not affected by the size of the bob and the angle of displacement. </li></ul>
  33. 33. Period of Pendulum Period = 0.35 x 4 = 1.40 s

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