WORKING SCIENTIFICALLY Flashcards
Name all SI Base Units
- Seconds
- Metre
- Ampere
- Kelvin
- Candela
- Mole
Define accurate
How close a measured value is to the true value
Define resolution
The smallest measuring interval on a measuring instrument
Define repeatable
If measurements are repeated by the same person in the same laboratory with the same equipment and the repeated results are close to each other
Define reproducible
if measurements are repeated by a different person or using different techniques and the results are close to each other
Define true value
The value that would have been obtained in an ideal measurement
Define uncertainty
the interval within which the true value can be considered to lie with a given level of confidence
Define error
the difference between the measurement result and the true value (not a mistake in the measurement)
Describe how to calculate the absolute uncertainty in a single reading
resolution/2
Describe how to calculate the absolute uncertainty in a set of repeated data
- first exclude anomalies.
Then calculate range.
- Absolute uncertainty = range/2
Describe how to calculate the percentage uncertainty in a set of repeated data
absolute uncertainty / mean value) x 100
Define precise
how close repeated measurements are to one another
Define Valid
a measurement is valid if it measures what it is supposed to be measuring
Describe how data with a systematic error would affect the appearance of a line of best fit on a graph:
it would adjust the value of the y or x intercept as every data point has the same
error
Describe how data with a random error would affect the appearance of a line of best fit on a
graph:
it would increase the spread of data around the line of best fit – both above and below the line
State the rules for finding the total uncertainty in a quantity calculated from the addition of 2 other quantities
eg. what is absolute uncertainty in A = B + C when B and C have absolute
uncertainties of +/- 0.5mm each:
- When combining quantities using addition, always add the absolute uncertainties.
- The absolute uncertainty in A would be 0.5 + 0.5 = 1.0 mm
State the rules for finding the total uncertainty in a quantity calculated from the multiplication
or division of 2 other quantities
eg. what is percentage uncertainty in A = BC^2 /D^ 4 when each
B, C and D have % uncertainties of 5%?:
when combining uncertainties for quantities that are multiplied or divided, always add
the percentage uncertainties.
1. When a quantity is raised to a power, multiply by the number in the power.
2. So in this case %U(A) = %U(B) + 2%U(C) + 4%U(D)
3. = 5 + 2 x 5 + 4 x 5 = 35%
Explain how to use a micrometer scale to measure the size of an object
- First read the main scale on the sleeve: identify how many whole millimeters there are and if there are any 0.5mm present too.
b. Then add the number shown on the thimble – where the horizontal line on the main scale intersects the thimble scale this is the number.
Describe 5 things to identify when criticising a table of results
- All data in a column should be to the same number of decimal places as the
resolution of an instrument - All data that has been calculated from raw data should be to the same number of significant figures as the raw data
- Repeats should be evident
- The range of the independent variable should be high
- At least 6 sets of results should be taken
Define directly proportional and describe its graphical appearance
- Two quantities are directly proportional if when one increases by a certain factor the other increases by the same factor
- It will be a straight line through the origin
