Module 2.1 - Physical Quantities, Units and Measurements Flashcards
1
Q
What is mass measured in?
A
kilogram, kg
2
Q
What is length measured in?
A
metre, m
3
Q
What is time measured in?
A
second, s
4
Q
What is temperature measured in?
A
kelvin, K
5
Q
What is electrical current measured in?
A
ampere, A
6
Q
What is amount of substance measured in?
A
mole, mol
7
Q
What is luminous intensity measured in?
A
candela, cd
8
Q
What is acceleration measured in?
A
metres per second squared, ms^-2
9
Q
What is density measured in?
A
kilograms per cubic metre, kgm^-3
10
Q
What is electric charge measured in?
A
coulomb, C
11
Q
What is energy measured in?
A
joule, J
12
Q
What is force measured in?
A
newton, N
13
Q
What is momentum measured in?
A
kilogram metres per second, kgms^-1
14
Q
What is potential difference measured in?
A
volt, V
15
Q
What is power measured in?
A
watt, W
16
Q
What is pressure measured in?
A
pascals, Pa
17
Q
What is velocity measured in?
A
metres per second, ms^-1
18
Q
What is the abbreviation of the prefix pico-, and what is it in standard form?
A
p, 10^-12
19
Q
What is the abbreviation of the prefix nano-, and what is it in standard form?
A
n, 10^-9
20
Q
What is the abbreviation of the prefix micro-, and what is it in standard form?
A
µ, 10^-6
21
Q
What is the abbreviation of the prefix milli-, and what is it in standard form?
A
m, 10^-3
22
Q
What is the abbreviation of the prefix centi-, and what is it in standard form?
A
c, 10^-2
23
Q
What is the abbreviation of the prefix deci-, and what is it in standard form?
A
d, 10^-1
24
Q
What is the abbreviation of the prefix kilo-, and what is it in standard form?
A
k, 10^3
25
What is the abbreviation of the prefix mega-, and what is it in standard form?
M, 10^6
26
What is the abbreviation of the prefix giga-, and what is it in standard form?
G, 10^9
27
What is the abbreviation of the prefix tera-, and what is it in standard form?
T, 10^12
28
What are the rules when estimating?
- round the estimate to the nearest power of 10
| - answer should be to the correct order of magnitude, within 1 power of 10 of the correct answer
29
What is the difference between human errors and random errors?
- human errors: often a 'one off' so results will be consistent when repeated so often easy to spot as will be wildly different from other repeats (a mistake)
- random errors caused by unknown/unpredictable changes during the experiment. May occur from changes in instruments/experimental conditions
30
What are some examples of random errors?
- variable heating in circuits causing variations in the current to be measured
- unexpectedly large extension of a metal wire due to a fault in its structure
31
What do systematic errors usually involve?
- measuring equipment
| - often present in all reading and can be removed once identified
32
Why may systematic errors occur?
- something wrong with the instrument or its data handling system
- the instrument is used wrong by the student conducting the experiments
33
What are some examples of systematic errors?
- scale printed on a metre is incorrect e.g. only 99cm long
- needle on an ammeter points to 0.1A when no current is flowing so recorded value will be 0.1A bigger than true value: a zero error (apparatus measures a non zero value when is should be measuring an exact zero value)
- thermometer has been incorrectly calibrated and is x°C higher/lower than true temperature
- parallax error caused by reading a scale at the wrong angle e.g. your eye is not parallel with meniscus on measuring cylinder
34
How do systematic errors affect accuracy?
- accuracy affected by systematic errors that's not accounted for as will be further from true value
- if systematic error is known, it can be taken into account and accuracy isn't affected
35
How do systematic errors affect precision?
doesn't affect precision as the apparatus has the same resolution
36
How do random errors affect accuracy?
can cause repeats above and below the true value
37
How do random errors affect precision?
repeating measurements identifies random errors so precision is unaffected
38
What is meant by the term 'absolute uncertainty'?
how large an uncertainty is. Has the same units as the quantity being measured
39
How do you work out the percentage uncertainty of a single value?
percentage uncertainty = (absolute uncertainty/measured value) x 100 %
40
How do you work out the percentage uncertainty for a number of repeat readings?
- take a mean
- find the range of the repeats
- halve the range to find the absolute uncertainty
- divide the absolute uncertainty by the mean and x 100
41
How do you work out the percentage uncertainty for a compound quantity in the form y=ab or y=a/b?
% uncertainty of y = % uncertainty of a + % uncertainty of b
42
How do you work out the percentage uncertainty for a compound quantity in the form y=a^n
% uncertainty of y = n x % uncertainty of a
43
What is meant by the term 'error bars'?
Represent the absolute uncertainty in measurements and can be plotted in the x and y directions
44
What is meant by the term 'worst line fit'?
The worst acceptable line, still passing through all the error bars. Either the steepest possible line of fit, or the least steep line of fit
45
How do you determine the uncertainty in the gradient from the maximum and minimum gradients?
1. Add error bars to each point. Size of the error bars is usually the same for each measurement
2. Draw a line of best fit, going through as many points as possible, ignoring anomalies
3. Calculate the gradient of the line of best fit
4. Do the same for the line of worst fit
5. Find the uncertainty of the graph, expressed as a positive value (the modulus): uncertainty = gradient of line of best fit - gradient of line of worst fit
6. Calculate the percentage uncertainty of the gradient: % uncertainty = (uncertainty/gradient of line of best fit) x 100
46
How do you determine the uncertainty in the y intercept from maximum and minimum gradients?
1. Draw the line of best fit and get the 'best' y intercept value
2. Draw maximum and minimum gradients and fine the max and min y intercept values
3. Determine the different between the max and min y intercepts and half it to find the y intercept uncertainty
4. percentage uncertainty = (uncertainty/best y intercept value) x 100
47
What is meant by the term 'systematic error'?
An error that does not happen by chance but instead is introduced by an inaccuracy in the apparatus or its use by the person conducting the investigation. This type of error tends to shift all errors in the same direction
48
What is meant by the term 'zero error'?
A type of systematic error caused when an instrument is not properly calibrated or adjusted, and so gives a non zero value when the true value is zero
49
What is meant by the term 'precision'?
The degree to which repeated values, collected under the same conditions in an experiment, show the same results
50
What is meant by the term 'accuracy'?
The degree to which a value obtained by an experiment is close to the actual or true value
51
What is meant by the term 'percentage uncertainty'?
The absolute uncertainty divided by the measured value expressed as a percentage
52
What is meant by the term 'percentage difference'?
The difference between 2 values, divided by the average and shown as a percentage
