Measurements

Question 1

What are the SI units?

Answer 1

• mass: kg (kilograms)
• length: m (metres)
• time: s (seconds)
• amount of substance: mol (moles)
• temperature: K (kelvin)
• electric current: A (amperes)
• light intensity - cd (candela)

Question 2

Prefixes from 10^12 to 10^-15

Answer 2

Tera - 10^12 - T
Giga - 10^9 - G
Mega - 10^6 - M
Kilo - 10^3 - k
centi - 10^-2 - c
milli - 10^-3 - m
micro - 10^-6 - µ
nano - 10^-9 - n
pico - 10^-12 - p
femto - 10^-15 - f

Question 3

What are random errors and how do you reduce the effect of them?

Answer 3

• errors that affect precisions
  Reduce with:
• take repeats and calculate means to identify anomalies
• using digital equipment to reduce human error and have smaller intervals
• use appropriate equipment

Question 4

What are systematic errors and how to reduce them?

Answer 4

• Systematic errors occur due to apparatus or faults in method
• affect accuracy as all results affected by it
  Reduce with:
• calibrate equipment (zero error)
• use digital measuring equipment
• use appropriate equipment

Question 5

What is absolute and percentage uncertainty?

Answer 5

Uncertainty: the bounds in which the two bounds lie
- Absolute: uncertainty as a fixed quantity
- Percentage: uncertainty as percentage of measurement

Question 6

How to tell uncertainty when not quoted?

Answer 6

For instruments with 2 judgments at the start and end (e.g. ruler), the uncertainty is +- the smallest increment.
For instruments with 1 judgement (e.g. top-pan balance), uncertainty is +- half of the smallest increment.

Question 7

What is uncertainty in a range of values?

Answer 7

• it is +- half of the range centred around the mean

Question 8

How to display uncertainties in graphs? How can you use this to find percentage uncertainty in gradient?

Answer 8

• Error bars extending from our point
• The percentage uncertainty can be found from the percentage difference between the best and worst gradient using the top and bottom of the first and last error bars

Question 9

How do uncertainties work when values are added or subtracted?

Answer 9

The absolute uncertainties are added as well for the result.

Question 10

How do uncertainties work when values are multiplied or divided?

Answer 10

The percentage uncertainties are added which can then be converted to the absolute uncertainties.

Question 11

How do you use orders of magnitude?

Answer 11

Powers of 10 are orders of magnitude, they can be used in standard form

Question 12

How to use estimation and why is it used?

Answer 12

• approximate values of physical quantities
• can be used for comparison or to check if a value is reasonable