WORKING SCIENTIFICALLY

Question 1

Name all SI Base Units

Answer 1

1. Seconds
2. Metre
3. Ampere
4. Kelvin
5. Candela
6. Mole

Question 2

Define accurate

Answer 2

How close a measured value is to the true value

Question 3

Define resolution

Answer 3

The smallest measuring interval on a measuring instrument

Question 4

Define repeatable

Answer 4

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

Question 5

Define reproducible

Answer 5

if measurements are repeated by a different person or using different techniques and the results are close to each other

Question 6

Define true value

Answer 6

The value that would have been obtained in an ideal measurement

Question 7

Define uncertainty

Answer 7

the interval within which the true value can be considered to lie with a given level of confidence

Question 8

Define error

Answer 8

the difference between the measurement result and the true value (not a mistake in the measurement)

Question 9

Describe how to calculate the absolute uncertainty in a single reading

Answer 9

resolution/2

Question 10

Describe how to calculate the absolute uncertainty in a set of repeated data

Answer 10

1. first exclude anomalies.

Then calculate range.

2. Absolute uncertainty = range/2

Question 11

Describe how to calculate the percentage uncertainty in a set of repeated data

Answer 11

absolute uncertainty / mean value) x 100

Question 12

Define precise

Answer 12

how close repeated measurements are to one another

Question 13

Define Valid

Answer 13

a measurement is valid if it measures what it is supposed to be measuring

Question 14

Describe how data with a systematic error would affect the appearance of a line of best fit on a graph:

Answer 14

it would adjust the value of the y or x intercept as every data point has the same
error

Question 15

Describe how data with a random error would affect the appearance of a line of best fit on a
graph:

Answer 15

it would increase the spread of data around the line of best fit – both above and below the line

Question 16

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:

Answer 16

1. When combining quantities using addition, always add the absolute uncertainties.
2. The absolute uncertainty in A would be 0.5 + 0.5 = 1.0 mm

Question 17

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%?:

Answer 17

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%

Question 18

Explain how to use a micrometer scale to measure the size of an object

Answer 18

1. 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.

Question 19

Describe 5 things to identify when criticising a table of results

Answer 19

1. All data in a column should be to the same number of decimal places as the
   resolution of an instrument
2. All data that has been calculated from raw data should be to the same number of significant figures as the raw data
3. Repeats should be evident
4. The range of the independent variable should be high
5. At least 6 sets of results should be taken

Question 20

Define directly proportional and describe its graphical appearance

Answer 20

1. Two quantities are directly proportional if when one increases by a certain factor the other increases by the same factor
2. It will be a straight line through the origin