Friday, August 14, 2015

Measurement Techniques | 9702 Physics Summary Notes

  • 2. Measurement Techniques | 9702 Physics Summary Notes





Quantity
Accuracy
Instrument
Length
1 cm
Tape
0.1 cm
Ruler
0.01 cm
Vernier caliper
0.001 cm
Micrometer screw gauge
Volume
1 cm3
Measuring cylinder
0.05 cm3
Pipette/burette
Angle
0.5o
Protractor
Time
1 min
Clocks
0.01 sec
Stopwatch
-axis scale
Time base of c.r.o
Temperature
1oC
Thermometer
0.5oC
Thermocouple
P.d.
0.01 V
Voltmeter
Current
0.01 A
Ammeter
0.0001 A
Galvanometer






2.1 Using a Cathode Ray Oscilloscope


Example: A supply of peak value 5.0 V and of frequency 50 Hz is connected to a c.r.o with time-base at 10 ms per division and Y-gain at 5.0V per division. Which trace is obtained?








2.2 Systematic and Random Errors

·  Systematic error:
o Constant error in one direction; too big or too small
o Cannot be eliminated by repeating or averaging
o If systematic error small, measurement accurate
o Accuracy: refers to degree of agreement between result of a measurement and true value of quantity.

·  Random error:
o Random fluctuations or scatter about a true value
o Can be reduced by repeating and averaging
o When random error small, measurement precise
o Precision: refers to degree of agreement of repeated measurements of the same quantity (regardless of whether it is correct or not)







2.3 Calculations Involving Errors

For a quantity x = (2.0±0.1)mm
· Absolute uncertainty = ∆x = ±0.1mm
· Fractional uncertainty = ∆x/x =0.05  
· Percentage uncertainty =  (∆x/x) × 100% = 5%
· Combining errors:
o When values added or subtracted, add absolute error
If p = (2x+y) / 3 or p = (2x-y) / 3, then ∆p = (2∆x+∆y) / 3
o When values multiplied or divided, add % errors
o When values are powered (e.g. squared), multiply percentage error with power
If r = 2xy3 or r = 2x / y3, then ∆r/r = ∆x/x+ 3 (∆y/y)




2.4 Treatment of Significant Figures

· Actual error: recorded to only 1 significant figure
· Number of decimal places for a calculated quantity is equal to number of decimal places in actual error.
· During a practical, when calculating using a measured quantity, give answers to the same significant figure as the measurement or one less








2.5 Micrometer Screw Gauge



·  Measures objects up to 0.01mm
·  Place object between anvil & spindle
·  Rotate thimble until object firmly held by jaws
·  Add together value from main scale and rotating scale




2.6 Vernier Scale


Measures objects up to 0.1mm
·  Place object on rule
·  Push slide scale to edge of object.
·  The sliding scale is 0.9mm long & is divided into 10 equal divisions.
·  Check which line division on sliding scale matches with a line division on rule
·  Subtract the value from the sliding scale (0.09×Divisions) by the value from the rule.



6 comments:

  1. Do you have solutions for 04/O/N/06 Question 2?

    ReplyDelete
    Replies
    1. See solution 984 at
      http://physics-ref.blogspot.com/2015/09/physics-9702-doubts-help-page-204.html

      Delete
  2. Hi can you please explain why it is impossible to measure time any closer than the nearest one tenth of a second using a stopwatch that has a precision of 0.01 s. Please reply asap I have a practical exam

    ReplyDelete
    Replies
    1. It's because of the human reaction time which is about 0.1s. We need to start and stop the clock manually.

      Delete
  3. Where is the solution of 9702 May/June 2010 variant 11

    ReplyDelete
    Replies
    1. For a list of worked past papers, go to
      http://physics-ref.blogspot.com/2014/05/physics-9702-notes-worked-solutions-for.html

      I believe that June 2010 Paper 11 and Paper 12 are almost similar, with only the question numbers changed. So, compared it with the paper 12 available there.

      Delete

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