Physical Quantities and Units (1) Flashcards
1
Q
How to represent a physical quantity
A
Must contain numerical value and unit in which it was measured in
2
Q
What is an estimation of diameter of an atom
A
10^-10m
3
Q
What is an estimation of the wavelength of UV radiation
A
10nm
4
Q
What is an estimation of the height of a human
A
2m
5
Q
What is an estimation of distance between Earth and Sun (1AU)
A
1.5x10^11m
6
Q
What is an estimation of the mass of a hydrogen atom
A
10^-27 kg
7
Q
What is an estimation of the mass of an adult human
A
70kg
8
Q
What is an estimation of the mass of a car
A
1000kg
9
Q
What is an estimation of the seconds in a day
A
90,000s
10
Q
What is an estimation of seconds in a year
A
3x10^7s
11
Q
What is an estimation of the speed of sound in air
A
300ms^-1
12
Q
What is an estimation of the power of a lightbulb
A
60W
13
Q
What is an estimation of the atmospheric pressure
A
1x10^5Pa
14
Q
What is the SI unit of mass
A
Kilogram (kg)
15
Q
What is the SI unit of time
A
Seconds (s)
16
Q
What is the SI unit of length
A
Metres (m)
17
Q
What is the SI unit of current
A
Ampere (A)
18
Q
What is the SI unit of temperature
A
Kelvin (K)
19
Q
What are derived units
A
Non-SI units
20
Q
What other ways can we write derived units
A
Combination of SI units through making a physical quantity equal to an equation where the other physical quantities can be given SI units
21
Q
What is homogeneity
A
Where the combined units on either side of an equation are the same
22
Q
What is the abbreviation and powers to 10 of tera
A
T-
10^12
23
Q
What is the abbreviation and powers to 10 of Giga
A
G-
10^9
24
Q
What is the abbreviation and powers to 10 of Mega
A
M-
10^6
25
What is the abbreviation and powers to 10 of Kilo
k-
10^3
26
What is the abbreviation and powers to 10 of Centi
c-
10^-2
27
What is the abbreviation and powers to 10 of Milli
m-
10^-3
28
What is the abbreviation and powers to 10 of Micro
μ-
10^-6
29
What is the abbreviation and powers to 10 of Nano
n-
10^-9
30
What is the abbreviation and powers to 10 of Pico
p-
10^-12
31
What is a true value
A perfect measurement value which reflects the quantity being measured with zero errors
32
What is the uncertainty
The uncertainty is an estimate of the difference between a measurement reading and the true value
33
What leads to uncertainty
Random and Systemic (zero errors) errors
34
What are random errors, their effect and how to reduce it
Random errors cause unpredictable fluctuations in an instrument’s readings as a result of uncontrollable factors, such as environmental conditions
This affects the precision of the measurements taken, causing a wider spread of results about the mean value
To reduce random error: repeat measurements several times and calculate an average from them
35
What are systemic errors, their effect and how to reduce it
Systematic errors arise from the use of faulty instruments used or from flaws in the experimental method
This type of error is repeated every time the instrument is used or the method is followed, which affects the accuracy of all readings obtained
To reduce systematic errors: instruments should be recalibrated or the technique being used should be corrected or adjusted
36
What is a zero error and its effect
Zero error is a type of systematic error which occurs when an instrument gives a non-zero reading when the true reading is zero
An example may be a set of mass scales showing a reading of 0.200 g when nothing is on the scales
This introduces a fixed error into readings which must be accounted for when the results are recorded
37
What is precision
The precision of a measurement is how close the measured values are to each other; if a measurement is repeated several times, then it can be described as precise when the values are very similar to, or the same as, each other
38
What is accuracy
The accuracy of a measurement is how close a measured value is to the true value; the accuracy can be increased by repeating measurements and finding a mean average
39
What is it called if something is measured to many decimal points
High resolution
40
What is the difference between uncertainty and error
Errors can be thought of as issues with equipment or methodology that cause a reading to be different from the true value
The uncertainty is a range of values around a measurement within which the true value is expected to lie, and is an estimate
For example, if the length of a box is measured multiple times as 12.55 cm, 12.45 cm and 12.51 cm, we can say the length is 12.50 cm with an uncertainty of 0.05 cm,
This is often written as 12.50 ± 0.05 cm
41
What 3 uncertainties are there
Absolute Uncertainty: where uncertainty is given as a fixed quantity (as above)
Fractional Uncertainty: where uncertainty is given as a fraction of the measurement
Percentage Uncertainty: where uncertainty is given as a percentage of the measurement
42
To find the uncertainties in certain situations
1. reading - voltmeter
2. measurement - ruler
3. repeated data
4. digital readings
The uncertainty in a reading (e.g. from a voltmeter): ± half the smallest division
The uncertainty in a measurement (e.g. from a ruler): at least ±1 smallest division
The uncertainty in repeated data: half the range i.e. ± ½ (largest - smallest value)
The uncertainty in digital readings: ± the last significant digit unless otherwise quoted
43
What is fractional uncertainty equal to
Uncertainty / measured value (without uncertainty)
This is only the uncertainty, for final answer add on measured value
Measured value ± fractional uncertainty
44
What is percentage uncertainty equal to
Uncertainty / measured value x 100%
This is only the uncertainty, for final answer add on measured value
Measured value ± percentage uncertainty
45
What is absolute uncertainty equal to
The uncertainty calculated from different situations as a numeral
Measured value ± uncertainty (calculated from different situations)
46
When combining two measurements do the uncertainties have to be combined too
True
47
What happens when adding/subtracting two uncertainties
Add/Subtract the main quantities
Add the absolute uncertainties
48
What happens when multiplying/dividing two uncertainties
Multiply/Divide main quantities excluding uncertainties
Convert all uncertainties to percentage form
Add their percentage uncertainties for total percentage uncertainty.
If you wish to convert to absolute, divide by 100 to go to decimal form and multiply by main quantities' value after it has gone through x or / for absolute uncertainty
49
What happens when raising the measurement to powers
Convert absolute uncertainties to percentage or fractional form
Multiply the fractional or percentage uncertainty by the power.
To go back to absolute uncertainty, multiply the percentage or fraction as decimal form by calculated value when subbing in main value into power.
50
What is distance
Distance is a measure of how far an object has travelled, regardless of direction
Distance is the total length of the path taken
Distance, therefore, has a magnitude but no direction
So, distance is a scalar quantity
51
What is displacement
Displacement is a measure of how far it is between two points in space, including the direction
Displacement is the length and direction of a straight line drawn from the starting point to the finishing point
Displacement, therefore, has a magnitude and a direction
So, displacement is a vector quantity
52
What is difference between displacement and distance
When a student travels to school, there will probably be a difference in the distance they travel and their displacement
The overall distance they travel includes the total lengths of all the roads, including any twists and turns
The overall displacement of the student would be a straight line between their home and school, regardless of any obstacles, such as buildings, lakes or motorways, along the way
53
What is speed
Speed is a measure of the distance travelled by an object per unit time, regardless of the direction
The speed of an object describes how fast it is moving, but not the direction it is travelling in
Speed, therefore, has magnitude but no direction
So, speed is a scalar quantity
54
What is velocity
Velocity is a measure of the displacement of an object per unit time, including the direction
The velocity of an object describes how fast it is moving and which direction it is travelling in
An object can have a constant speed but a changing velocity if the object is changing direction
Velocity, therefore, has magnitude and direction
So, velocity is a vector quantity
55
List all the vectors
Displacement
Velocity
Acceleration
Force
Momentum
56
List all the scalars
Distance
Speed
Mass
Time
Energy
Volume
Density
Pressure
Electric charge
Temperature
57
How are vectors represented
Vectors are represented by an arrow
The arrowhead indicates the direction of the vector
The length of the arrow represents the magnitude
58
How to do the triangle method
To combine vectors using the triangle method:
Step 1: link the vectors head-to-tail
Step 2: the resultant vector is formed by connecting the tail of the first vector to the head of the second vector
To subtract vectors, change the direction of the vector from positive to negative and add them in the same way
59
How to do the parallelogram method
To combine vectors using the parallelogram method:
Step 1: link the vectors tail-to-tail
Step 2: complete the resulting parallelogram
Step 3: the resultant vector is the diagonal of the parallelogram
60
How do I find the magnitude of the vector after triangle method + parallelogram method
Pythag or Trig
61
What is the resultant vector
When two or more vectors are added together (or one is subtracted from the other), a single vector is formed, known as the resultant vector
62
What are coplanar forces
Forces that act on the same plane
63
How are coplanar forces represented
Coplanar forces can be represented by vector triangles
64
What happens when coplanar forces are in equilibrium
Coplanar forces can be represented by vector triangles
In equilibrium, these are closed vector triangles.
The vectors, when joined together, form a closed path
65
What is a resolving vector
Two vectors can be represented by a single resultant vector that has the same effect
A single resultant vector can be resolved and represented by two vectors, which in combination have the same effect as the original one
When a single resultant vector is broken down into its parts, those parts are called components
The resultant force will be the diagonal force and a horizontal and vertical force will manifest to the sides and will aim to force half a rectangle. Using trigonometry and closing the triangle, we can find these horizontal and vertical forces
66
What happens when you inverse a percentage uncertainty
It remains the same because you are dividing 0% uncertainty by x% uncertainty, leading to 0+x%
67
What happens when you multiply/divide an uncertainty by an integer
The uncertainty is multiplied/divided by the integer
3 x 3.0 ± 2cm = 9 ± 6cm
68
If y is proportional to x what does the graph look like
Straight line through the origin
69
If y is proportional to x^2 what can the 3 graphs look like
1. Y and X axis - Right side of positive parabola
2. Y and X^2 axis - Straight line through the origin
3. Square root Y and x axis - Straight line through the origin
70
If y is proportional to root x what do the 2 graphs look like
1. y and x axes - left side of negative parabola
2. y and root x axes - straight line through the origin
71
If y is proportional to 1/x or inversely proportional to x what doe the 2 graphs look like
1. y and x axes - left side of positive parabola
2. y and 1/x axes - straight line through origin
72
If y is inversely proportional to x^2 what doe the 3 graphs look like
1. y and x axes - left side of positive parabola where x and y axis do not touch
2. y and 1/x axes - right side of positive parabola
3. y and 1/x^2 axes - straight line through origin
