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MEASUREMENTS TECHNIQUES, Screenshot (9) - Coggle Diagram

- - - - the smallest scale is 1mm, therefore the 0.5mm
      - possible errors
        
        calibration of the meter rule
        
        parallax error
        
        systematic errors when end of the rule is worn out
    - - can measure up to an accuracy of 0.01cm or 0.1mm
      - used to measure the internal and external diameters of tubes and length of a small object
      - reading a vernier calliper
        
        check for zero error
        
        zero error = 0
        
        the zero of the vernier scale is exactly in line with the zero of the main scale
        
        zero error positive >0
        
        the zero of the vernier scale is on the right of the zero of the main scale
        
        zero error negative <0
        
        the zero of the vernier scale is on the left of the zero of the main scale
        
        read the main scale
        
        take the reading from the main scale up to the mark just before the zero line of the vernier scale. This give the reading (in cm) up to the first decimal point
        
        read the vernier scale
        
        take the mark from the vernier scale which coincidence with a line on the main scale. This gives the second decimal places
        
        the final reading
        
        final reading= (main scale+vernier scale)-zero error
    - - can measure up to an accuracy of 0.01mm
      - reading a micrometer screw gauge
        
        check for zero error
        
        💫 zero error = 0
        
        the zero on the thimble scale is in line with the datum line
        
        💫 zero error positive ( >0 )
        
        the zero of the thimble scale is on the below the datum line
        
        💫 zero error negative ( <0 )
        
        the zero of the thimble scale is above the datum line
        
        read the sleeve scale
        
        take the reading on the sleeve scale up to the edge of the thimble.
        the sleeve scale gives the reading in mm with one decimal place
        
        read the thimble scale
        
        take the thimble scale reading at the mark which coincides with the datum line.
        the thimble scale gives the reading (in mm) of the second and two decimal places.
        
        the final reading
        
        Final reading = (sleeve scale + thimble scale) — zero error
  - - - ensure that the initial (unloaded) reading is zero
      - there is a control for adjusting the zero reading, it may have a tare facility
    - - should be careful of zero error, usually has a zero error adjustment screw
      - parallax can occur during the reading is taken
    - - unknown mass is balanced by a slider, calibrated in mass unit
      - should be aware of zero error and parallax error
  - - - Measure short intervals of time
        
        Digital stopwatch
        
        can measure up to 0.1 seconds
        
        Analogue stopwatch
        
        can measure up to 0.01 seconds
- - - - 🎈causes readings to vary around the mean value
        🎈can be reduced by repeating measurements and calculate average
      - example : PARALLAX ERROR
        
        caused when the eyes are at the wrong position with the reading scales
    - - example : ZERO ERROR
        
        caused when an instrument gives a non-zero reading when the true value of quantity is zero
      - 🎈causes readings to differ from true value by a consistent amount each time the reading is taken
        🎈constant error, CANNOT be eliminated by averaging, can be deduct by adding or substracting
    - - 🎈the degree of exactness to which a measurement can be reproduced
        🎈how close the readings are to each other
        
        example :
        “A metre ruler can take measurements up to 0.1cm while a micrometer screw gauge can take measurements up up to 0.001cm”
        ➡️ Precision of micrometer screw gauge >> metre ruler
    - - 🎈how well the measurements taken with an accepted value
        🎈how close the data obtained is to the actual value
  - - - no measurement is absolute, therefore measurements must be written together with uncertainty
      - e.g. L= 2.5 ± 0.1 cm
      - generally, all readings can be recorded in the form R ± ΔR in which ΔR is the actual uncertainty and R is the reading
      - the actual uncertainty in the scale reading of an instrument is generally taken as ½ the smallest graduation
      - e.g. If the limit of the reading is 0.1 cm then the uncertainty range is ±0.05 cm. this is the absolute uncertainty
    - - % uncertainty= (absolute uncertainty/reading) x 100
    - - subtraction and addition: y=b-c, y ± Δy=(b-c) ± (Δb+Δc)
      - multiplication and division: (add percentage/fractional uncertainties)
        
        y= b x c, then (Δy/y)=(Δb/b)+(Δc/c)
        
        Δy is the absolute uncertainty
        
        when using powers, multiply the % uncertainty by the power. z=b^a, then (Δz/z)=a(Δb/b)