measurements and errors Flashcards

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1
Q

what are the base SI units

A

Candela- cd (Luminos intensity), Metre- m (length), Kelvin- K (temperature), Mole- mol (chemical mass), Ampere- A (electrical current), kilogram- Kg (mass), Second- s (time)

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2
Q

What are other useful SI units

A

Celsius- `C (temperature), Joule- J (energy), Ohm- omega (resistance), Tesla- T (magnetic flux density), Hertz- Hz (frequency), Pascal- Pa (pressure), Newton- N (force), Coulomb- C (charge), Watt- W (power), Volt, V (P.d)

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3
Q

unit prefixes

A

Nano- nm (10^-9), Micro- um (10^-6), Milli- m (10^-3), Centi, c (10^-2), kilo- K (10^3), Mega- M (10^6), Giga- G (10^9)

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4
Q

what are the observed value, true value and error

A

observed value- the measurement you make
True value- what the measurement should be
error- uncertainty about our measurement (the difference between observed and true value)

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5
Q

the 2 parts of an error model

A

random error- follows no pattern (reduced by doing experiment multiple times)
Systematic error- follows a set pattern also known as zero error (reduced by calibration e.g weighing a known mass)

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6
Q

what is the precision of the measurement system

A

how close repeated measurements are to each other

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7
Q

what makes a measurement repeatable

A

if the same person does the same experiment with the same apparatus and gets the same results

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8
Q

what makes a measurement reproducible

A

if a different person can perform the experiment with the same apparatus and get the same result

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9
Q

what is the resolution of a measuring instrument

A

it describes its maximum precision

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10
Q

define uncertainty

A

a measure of how confident you can be in a measurement

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11
Q

what is the absolute uncertainty

A

The range of possible real values (e.g + or - 5)

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12
Q

what is the fractional uncertainty and percentage uncertainty

A

the absolute uncertainty divided by the measured value (percentage uncertainty is this as a per cent)

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13
Q

what is an error bar

A

a line on an uncertainty graph showing the range of possible values. they can be used to find the steepest and shallowest line of best fit

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14
Q

how can uncertainty be spotted from a graph

A

if the theory and the results do not match when the independent variable is zero

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15
Q

how do you calculate the uncertainty in a measurement on a graph

A

the steepest possible line of best fit has a gradient g1
the shallowest possible line of best fit has a gradient of g2.
uncertainty= (g1+g2)/2 + or - (g1-g2)/2

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16
Q

what is meant by validating knowledge

A

confirming that it is correct