Topic 2 - Measurement Techniques

Question 1

Systematic Errors

Answer 1

Errors of measurement which yield a consistent overestimation or underestimation of the actual value.

• low accuracy
• definite causes
• reproducible
• can be eliminated

Question 2

Examples of systematic errors

Answer 2

• Zero errors of measuring instruments
• Inaccurately calibrated instruments
• Human reaction time
• Wrong assumptions
• Background count rate of GM counter

Question 3

How to eliminate systematic error?

Answer 3

• Calibration curves
• Take account of zero error
• Press zero before measuring mass

Question 4

Random Errors

Answer 4

Scatter of reading about a mean value //

Irregularity of a quantity measured

• low precision
• no specific causes
• not reproducible
• cannot be eliminated, only can be reduced

Question 5

Examples of random errors.

Answer 5

• Fluctuations in external conditions

• Temperature
• Air pressure
• Friction

• Human limitations
- human reaction time

• Parallax error
• Carelessness
• Wrong techniques

Question 6

Ways to reduce random errors?

Answer 6

• Take average of repeated readings
• Plot a graph and draw best fit line
• timing a large number of oscillations

Question 7

Precision

Answer 7

(def.) degree of closeness between several measurements of a physical quantity

• refers to extent or limit of sensitivity of a measuring instrument

• refers to degree of scattering of date
- differences between measured values

Question 8

Accuracy

Answer 8

(def.) defree of closeness of a measured quantity to its actual value

• refers to percentage uncertainty of a measured quantity

• depends on magnitude
• depends on instruments used
• depends on technique used

• how close the data obtained to its actual value

Question 9

How dimension affects accuracy?

Answer 9

bigger dimensions - smaller uncertainty

hence, higher accuracy

Question 10

Uncertainties

Answer 10

(def.) total range of values within which the measurement is likely to lie.

ALWAYS ONE SF ONLY

• Actual / Absolute uncertainty :
(max reading - min reading) / no. of reading

• Fractional uncertainty :
Δy/y

• percentage uncertainty :
Δy/y x 100

Question 11

Consequential uncertainties

Answer 11

overall uncertainty of the final results.

• Addition and subtraction :
- always add the absolute uncertainties

• Product and quotient :

• Δy/y = Δa/a + Δb/b
• (Δy/y x 100)= (Δa/a x 100) + (Δb/b x 100)

• Involving Power
- n times of the uncertainty

• Involving constant

• both the value and uncertainty must be times with the constant
• example :

y = 4a
y = 4(a +- Δa)
y = 4a +- 4Δa