Measurements and errors

• What are the fundamental SI units for mass?

  kg (kilograms)
• What is the SI unit for length?

  m (metres)
• What is the SI unit for time?

  s (seconds)
• What is the SI unit for the amount of substance?

  mol (moles)
• What is the SI unit for temperature?

  K (kelvin)
• What is the SI unit for electric current?

  A (amperes)
• How can SI units be derived?

  By using their equations, e.g., F=ma
• What are the SI units of force (F)?

  $kg \cdot m \cdot s^{-2}$
• How are the SI units of voltage calculated?

  By using energy and charge equations
• What is the SI unit for energy?

  kg$\cdot m^{2} \cdot s^{-2}$
• What is the conversion factor from MeV to joules?

  1 eV = $1.6 \times 10^{-19} J$
• How do you convert 76 MeV to joules?

  76 MeV = $1.216 \times 10^{-11} J$
• How is 1 kWh converted to joules?

  1 kWh = $3.6 \times 10^{6} J$
• What do random errors affect in measurements?

  Precision of the measurements
• What is an example of a random error?

  Electronic noise in instruments
• How can random errors be reduced?

  Take at least 3 repeats and calculate mean
• What do systematic errors affect in measurements?

  Accuracy of the measurements
• What is an example of a systematic error?

  Zero error in balances
• How can systematic errors be reduced?

  Calibrate apparatus with known values
• What is precision in measurements?

  Consistency of measurements around a mean
• What is repeatability in experiments?

  Same results by the original experimenter
• What is reproducibility in experiments?

  Same results by different experimenters
• What is resolution in measurements?

  Smallest change that gives a reading
• What does accuracy in measurements refer to?

  Closeness to the true value
• What is uncertainty in a measurement?

  Bounds in which the true value lies
• What is absolute uncertainty?

  Uncertainty as a fixed quantity
• What is fractional uncertainty?

  Uncertainty as a fraction of measurement
• What is percentage uncertainty?

  Uncertainty as a percentage of measurement
• How can you reduce percentage and fractional uncertainty?

  By measuring larger quantities
• How is uncertainty in a reading determined?

  ± half the smallest division
• How is uncertainty in a measurement determined?

  At least ±1 smallest division
• How is uncertainty in repeated data calculated?

  Half the range of values
• How can uncertainty be reduced when measuring time for a pendulum swing?

  By measuring multiple instances
• How should uncertainties be reported?

  To the same significant figures as data
• How do you combine uncertainties when adding data?

  Add absolute uncertainties
• How do you combine uncertainties when multiplying data?

  Add percentage uncertainties
• How do you find the percentage uncertainty when raising to a power?

  Multiply percentage uncertainty by power
• What are orders of magnitude?

  Powers of ten describing object sizes
• How do you estimate the area of a hydrogen atom?

  Using the formula $A =$$\pi r^{2}$
• Why is estimation important in physics?

  To approximate values and check reasonableness