UNIT 11 - Measruement And Data Processng And Analysis

Question 1

Give reason for the use of a log scale on graphs.

Answer 1

Allows some relationships to be rearranged into a form of a straight line.

Question 2

State why is propagation of uncertainties important.

Answer 2

Uncertainties in raw data lead to uncertainties in processed data and must be propagated throughout the experiment in a consistent manner.

Question 3

How to calculate absolute uncertainty in ab or a/b?

Answer 3

1. find the percentage uncertainty in a and b.
2. add them to find the %uncertainty in the value.
3. convert to an absolute value.

Question 4

Distinguish the characteristics and causes of random and systematic error and give examples.

Answer 4

Random:
can be reduced through repeated measurements

caused by:
- the readability of the measuring instrument
- the effects of changes in the surroundings (e.g. temp).
- insufficient data
- misinterpretation by the observer

Systematic:
cannot be reduced by repeating the experiments.

caused by:
- poor experimental design/produce
- lack of necessary knowledge

Question 5

State how to calculate sum of the absolute uncertainties when adding, subtracting, multiplying od dividing measurements.

Answer 5

The uncertainty is calculated as a sum of the absolute uncertainties.

Question 6

What should a graph contain?

Answer 6

• title
• axes labelled with both quantities and units
• space used as effectively as possible
• sensible linear scales - no uneven jumps
• all points plotted correctly
• line of best fit

Question 7

How to calculate uncertainty in analogue and digital instruments?

Answer 7

analogue:
some state the degree but if they do not it is half of the smallest division.

digital:
the smallest scale division.

Question 8

State the formula for percentage uncertainty.

Answer 8

percentage uncertainty = (absolute uncertainty/measured value)x100%

Question 9

Distinguish accuracy and precision.

Answer 9

precision- how close the results are to each other, the smaller the random uncertainties.

accuracy - comparing what you obtained to what you should get, the smaller the systematic error.

Question 10

To how many SF the answer should always be when adding, subtracting, dividing or multiplying?

Answer 10

To the least precise data.

Question 11

Distinguish the terms repeatable and reproductible.

Answer 11

repeatable - the same person duplicates the experiment with the same results.

reproductible- several experiments duplicate the results.

Question 12

Define the terms extrapolation and interpolation.

Answer 12

extrapolation - extending a best-fit line beyond the range of measurements of the graph.

interpolation - assuming that the trend line applies between two points.

Question 13

State the formula for and define the percentage error.

Answer 13

Is a measure of how close the experimental value is to the literature/accepted on.

PE= (|accepted value-experimental value|/accepted value)x100%

Question 14

List and define the analytical techniques.

Answer 14

• qualitative analysis - the detection of presence but not the quality of a substance in a mixture.
• quantitative analysis- measurement of the quantity of a particular substance in a mixture.
• structural analysis- description of how the atoms are arranged in molecular structures.

Question 15

What is parallax error?

Answer 15

Reading the burette from an incorrect angle.