Measurements and Their Errors Flashcards

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1
Q

What are the SI Units

A
  • Mass (kg)
  • Length (m)
  • Time (s)
    Amount of substance (mol)
    Temperature (K)
  • Electric current (A)
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2
Q

What are the Unit Prexfixes you need to know

A
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3
Q

How do you convert between Electron Volts and Joules

A

1eV = 1.6x 10^-19 J

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4
Q

What is Random Error

A
  • Measurments vary due to unpredictable circumstance
  • They cannot be corrected and can only be minimised by making more measurements and calculating a mean
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5
Q

How do you reduce Random Error

A
  • Take at least 3 random repeats and calculate a mean (shows anomalies)
  • Use computers/cameras to reduce human error and increase precision
  • Use appropriate equipment (micrometers rather than ruler)
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6
Q

What is Systematic Error

A
  • Measurements differ from the true value by a consistent amount each time
  • Can be corrected by using a different technqiue
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7
Q

How do you reduce Systematic Error

A
  • Calibrate the equipment by measuring a known value
  • In radiation experiments correct for background radiation by measuing it beforehand
  • Look at readings at eye level to reduce parallax error
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8
Q

What is Precision and Accuracy

A
  • Precision - how close measurments are to each other and the mean
  • Accuracy - how close a measurment is to the true value
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9
Q

What does Repeatable, Reproducible and Resolution mean

A

Repeatable - when the original experimenter repeats the investigation using the same method and equipment and gets the same results

Reproducible - when somebody else using different equipment repeats the investigation and gets the same results

Resolution - the smallest change in a quantity being measured

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10
Q

What is the Uncertainty in a Reading and in a Measurement

A
  • The uncertainty in a reading (when one value is found) is ± half the resolution
  • The uncertainty in a measurement (when the difference between two readings is found) is ± 1 resolution
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11
Q

How is Uncertainty showed for Repeated Data

A

mean ± range/2

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12
Q

How do you combine Uncertainties

A
  • Adding/ subtracting data - Add Absolute Uncertainities
  • Multiplying/ dividing data - Add Percentage Uncertainities
  • When raising data with an uncertainity to a power - Multiply the Percentage Uncertainty by the Power
  • When multiplying data with an uncertainty by a constant - multiply the absolute uncertainty by the constant but not the percentage uncertainty
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13
Q

How do you find Percentage Uncertainties using Graphs

A
  • Draw a steepest and shallowest line of worst fit that goes through all of the error bars
  • Calculate the gradient of the lines
  • The uncertainty is the difference between the best and worst gradients

Percentage Uncertainty = Best Gradient - Worst Gradient / Best Gradient x 100

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