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 cm^{3}

Measuring cylinder

0.05 cm^{3}

Pipette/burette


Angle

0.5^{o}

Protractor

Time

1 min

Clocks

0.01 sec

Stopwatch


axis scale

Time base of c.r.o


Temperature

1^{o}C

Thermometer

0.5^{o}C

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 timebase at 10 ms per division and Ygain 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 = (2xy) / 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 = 2xy^{3} or r = 2x / y^{3}, 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.
Do you have solutions for 04/O/N/06 Question 2?
ReplyDeleteSee solution 984 at
Deletehttp://physicsref.blogspot.com/2015/09/physics9702doubtshelppage204.html
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
ReplyDeleteIt's because of the human reaction time which is about 0.1s. We need to start and stop the clock manually.
Delete