Measurements & Uncertainties

Question 1

What are the fundamental SI measurements and units?

Answer 1

Time                       - Second (s)
Length                    - Meter (m)
Mass                       - Kilogram (kg)
Temp.                      - Kelvin (K)
Quantity of matter  - Mole (mol)
Electric current       - Ampere (A)
Luminous intensity - Candela (cd)

Question 2

What is the rule for Significant figures when doing calculations?

Answer 2

The result must have the same s.f as the LEAST KNOWN (lowest s.f) number in the operation

Question 3

What are Random Uncertainties

Answer 3

• no trend, just crazy values

* You can reduce this error by averaging many measurements: (1+2+3+4)/4=Average value

Question 4

What are Systematic Uncertainties

Answer 4

• Due to incorrectly calibrated instruments
• all data will be offset by the same value
• you can’t reduce this by averaging.

Question 5

Define Accurate Measurements

Answer 5

Measurements with small SYSTEMATIC error

Question 6

Define Precise Measurements

Answer 6

Measurements with small RANDOM error

Question 7

Rule of Uncertainties for Addition/Subtraction

Answer 7

Add the ABSOLUTE uncertainties together

Question 8

Rule of Uncertainties for Multiplication/Division

Answer 8

Add the FRACTIONAL uncertainties together

Question 9

Rule of Uncertainties for Exponents (a^4)

Answer 9

Multiply the Exponent to the FRACTIONAL uncertainty (this will be treated as the new “Fractional Uncertainty” for that term)

Question 10

How to calculate FRACTIONAL uncertainty and PERCENTAGE uncertainty

Answer 10

FRACTIONAL:
“ABSOLUTE uncertainty” divided by “measured value”

PERCENTAGE:
Multiply FRACTIONAL by 100