Working scientifically 1 - 33

Meanings of prefixes : Pico , nano, micro, milli, kilo, mega, giga, tera

10 to power of : -12, -9, -6, 3, 6, 9, 12

Base quantities and their units

1. length - meter (m)

2. temperature - kelvin (k)

3. current - ampere (a)

4. time - second (s)

5. luminous intensity - candela (cd)

6. mass - kilogram (kg)

7. amount of subsance - mol

Define accuracy

how close a measured value is to the true value

Define precise

how close repeated measurements are to one another

Define resolution

the smallest measuring interval on a measuring instrument

define valid

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

define repeateable

if measurements are repeated by the same person in the same laboratory with the same equiptment and the repeated results are close to each other

define reproducible

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

define true value

the value that would have been obtained in an ideal measruement

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 MEASURMENT)

A student comments that the measurment of 2.40V is more precise than the measurement of 2.4V. Explain why they are incorrect

1. precision is a measure of the closeness of repeated measurements

2. both 2.40V and 2.4V are single measurements so we cannot comment on their ‘precision’

3. the result 3.40V has been measured using a higher resoltuion multimeter

4. so 2.40V has a lower absoulte uncertatinty (0.005V as compared to 0.05V)

explain why doing repeat measruements increases the likelihood of an accurate measurement

repeating measurments reduces the effect of random error

describe how data with a systematic error would affect the appearance of a line of best fit on a praph

it would adjust the value of the y or x intercept a 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 spead of data around the line of best fit - both above and below the line

how to calculate the absolute uncertainty in a single reading

absolute uncertainty in a single reading = resolution / 2

how to calculate absolute uncertainty in a set of repeated data

1. exclude anomalies/

2. calculate range

3. absolute uncertainty = range / 2

formula for calcuating percentage uncertainty with a single measurment

= absolute uncertainty / measurement x 100

formula for calculating percentage uncertainty with repeats

absolute uncertainty / mean value x 100

experimental choices to make to increase the likelihood of getting an accurate result

1. aim to reduce the percentage uncertainty in the measurments

2. to do this choose equiptment with a high resolution - this will have a low absolute uncertainty resulting in a low percentage uncertainty

   1. or if possible, increase the measurement we are taking. for same absolute uncertainty this will reduce percentage uncertainty

why is dropping a ball from an upstairs window instead of a lower one for an experiement more likely to produce an accurate result?

the time taken for the ball to fall will increase. this will reduce the percentage uncertainty in the measurement of time

how to calcualte absolute uncertainty in a measurment when given its percentage uncertainty

absolute uncertainty = (percentage uncertainty / 100) x mean value

state the range of values a measured value can take when given its percentage uncertainty e.g

resistance = 4ohms +- 2%. what is the range of resistance

1. find absol uncertainty = 2/100 × 4 = 0.08

2. resistance = 4=- 0.08

   1. min res = 3.92, max res = 4.08

examples of things that may have a caused a result to be inaccurate

1. parallax error introduces random error (e.g viewer looking at scales from different angles)

2. systematic error (view consistently looks at scale from wrong angle)

   1. zero error may introduce systematic error

what is zero error and how can we correct it

zero error is a systematic error that occurs when a measuring instrument does not display ecactly zero when no object is being measured. to correct it you should subtract or add the zero error.

why is a digital thermometer a better choice of a device than a glass thermometer to measure tempertature

a digital thermometer has a higher resolution leading to a measurement with a lower absolute uncertainty and therefore lower percentage uncertainty

a digital thermomemter also avoids parallax error

5 things to identify when criticisng a table of results

1. all data in a colum should be to the same number of deciaml places as the resoltuion of the instrument

2. all data that has been calculated from raw data should be to the same sf as raw data

3. repeats should be evident

4. range of independent variable should be high (and first in column and on x axis)

   1. 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. the graph would loook like a straight line going through the origin.

look at questions 28 onwards on doc