Analytical skills Flashcards

1
Q

Base units + measurements

  1. Magnitude?
  2. Orders of Magnitude?
  3. Unit?
  4. Standard form?
A
  1. A Magnitude – size of the number
  2. Orders of Magnitude - the approximate size of a quantity/measurement
  3. A Unit – based on a comparison with an agreed standard (convert to same unit)
  4. Standard form as: A x 10^n
    (A has to be a whole number between 1-10)
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2
Q

What are the 2 standards/ types of scientific measurements?

A
  1. SI Base quantities
    (international system of units - system of agreed units, recognised by everyone + used in science, industry + medicine)
  2. The Metric system
    (Modern approach to units)
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3
Q

1.

The international system of units
SI

What are the 7 base units + their symbols?

A

THE SI BASE UNITS:

  1. Electric current: Ampere (A)
  2. Luminous intensity: Candela (cd)
  3. Thermodynamic temperature: Kelvin (K)
  4. mass: Kilogram (Kg)
  5. length: Metre (m)
  6. amount of substances: Mole (mol)
  7. time: Second (s)

Quantity: base unit (symbol)

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4
Q
  • Derived SI based units?
  • Base units for these?
A

Derived (SI) units

  • units defined by a combination of base units
    (eg metres pr second [m/s^-1], metres squared for area)

Base units r based on an absolute standard that’s easily reproducible

  • All other units are derived from the base units = known as derived units

EG

  • Speed (ms-1- metres pr second) is a derived unit
    = it uses two base units: metre and second
  • Density = kgm-3
  • Pressure = N/m2
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5
Q

2.

The metric system

A
  • A Modern approach to weights + measures
  • Uses units such as metres, litre, gram to measure length, liquid volume +mass
Property - Unit - Symbol
  • Length - metres - m
  • Mass - gram - g
  • Volume - Litre - L
  • Time - second - S
  • Temperature - celsuius - °C
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6
Q

Metric system prefixes

A
  • Based on the powers of 10 to express multiples /subdivisions of units
  • SI base units can be converted into more appropriate units for the quantity being measured, by adding a prefix to the name of the base unit

2.56 cm
C – the prefix (centimetres)
m – the unit (metres)

1 cm3 = 1 mL = 0.001 L

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7
Q

Metric conversions

A
  • cm –> dm [/10] –> m [/10]
  • cm2 –> dm2 [/100] –> m2 [/100]
  • cm3 –> dm3 [/1000] –> m3 [/1000]
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8
Q

LEARN CONVERSIONS BETWEEN UNITS

A

CHECK ‘REVISION’ PPT ON CANVAS FOR PRACTICE

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9
Q

Errors

Accuracy?

A
  • Accuracy is a measure of how close values are to the accepted standard value for a quantity
  • Is also know as trueness
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10
Q

Precision?

A
  • Precision the closeness of two or more measurements to each other
  • EG u weigh a substance 5 times + get 3.2 g each time
  • Precision is independent of accuracy
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11
Q

List ways of improving the precision of
measurements

A
  • Using instruments with finer scale divisions
  • Repeat reading = 3 repeats + take average
  • Record figures correctly
  • Measuring/counting a group of >10 - Using large sample sizes
  • Checking for zero errors
  • Checking calibration of instruments
  • Make sure equipment used is clean, no air bubbles etc
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12
Q

errors (±) can be expressed as ‘absolute’ errors or as a%

Absolute error?

A
  • Absolute Error is the difference between the actual + measured value
  • Absolute error = ½ x smallest division (of the measurement)

EG 8.3 ± 0.05cm [as it was going up by 0.1cm]

ALWAYS NEED TO ADD THE ± SIGN OR LOSE MARKS

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13
Q

Relative error?

A
  • Relative Error is the Absolute Error divided by the actual measurement
  • Relative error = Absolute error / Actual measurement

EG 0.05 / 8.3 = ±0.006

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14
Q

Percentage error?

A
  • The Percentage Error is the Relative Error shown as a percentage
  • Absolute error / actual measurement x100

EG 0.05 / 8.3 x100 = ±0.6%

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15
Q

COMBINING ERRORS RULES

  1. When you add / subtract 2 numbers with errors?
  2. When you multiply divide 2 numbers with errors?
  3. When values are raised to a power / fraction?
A
  • Rule 1: When you add / subtract 2 numbers with errors = add the absolute errors
  • Rule 2: When values are multiplied / divided the percentage errors are ADDED
  • Rule 3: When values are raised to a power OR
    fraction e.g. y^2 the percentage errors are
    MULTIPLIED by the power
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16
Q

Data analysis

Graphs
- X and Y axis?

S.A.L.T ?

A
  • Independent variables = X axis (Horizontal) [variable being changed]
  • Dependent variables = Y axis (Vertical) [variable affected + measured]
  • Axes need labels in the form: Quantity/unit
    e.g. Time/minutes. distance/cm. volume/cm³

S- Scale
A- Axis
L- Labels
T- Title

  • draw full triangles on tangent for gradient
17
Q

Rates of change?

A
  • The gradient of a graph plotted against time will be the “rate of change” of the dependent variable
  • eg how much its value
    (volume, temperature- this is y) changes per second, minute, hour etc
18
Q

relationships between variables

Relationships can be…

➢ Linear
➢ Non-linear
➢Directly proportional
➢Inversely proportional

A

Linear: The two variables give a straight line graph.

Non-linear: The rate of increase in one variable = not the same as the rate of increase in the other variable = curved line on a graph

Directly proportional: as one increases, the other increases by the same percentage [y ∝ x or
y=mx….straight + ALWAYS passes by the origin]

Inversely proportional: when one value decreases at the same rate that the other increases.
[x ∝ 1/y or y =𝟏/𝒙]

19
Q

How to convert Inversely proportional graphs into straight line graphs

A

for each value in the ‘Y’ axis = do 1÷ Y for each of them = plot these new values [use same x values]

1 / y