Practical physics

• Whats the difference between a base unit and a derived unit


  A base unit is one of the seven fundamental units.

  A derived unit is derived by the multiplication or division of units
• Whats the order of scale unit


  • Nano 10^-9
  • Micro 10^-6
  • Milli 10^-3
  • Centi 10^-2
  • Deci 10^-1
  • Kilo 10^3
  • Mega 10^6
  • Giga 10^9
  • Tera 10^12
• Independent variables


  The variable that you change within an investigation
• Dependent variables


  The variable that are observed or measured
• What is precision


  Precision is determined by the consistency of results, if a measurement is precise values cluster closely together.

  Its influenced by random errors
• What is accuracy


  Accuracy is determined by how close the measurement is to the true value

  Its influenced by random and systematic errors
• What is an error


  Error is the difference between the measurement and true value
• What is a uncertainty


  Uncertainty is the interval within which the true value can be considered to lie with a given level of probability

  Its determined by apparatus and variables
• How do you work out percentage uncertainty


  Percentage uncertainty = uncertainty / measurement x 100
• How can you tell if a result is an anomaly


  A value is an anomaly if it doesnt follow the pattern of results
• What does repeatable mean


  Measurements are repeatable when similar results are obtained from by students from the same group using the same method
• What does reproducible mean


  Measurements are reproducible when similar results are obtained by students from different groups using different methods or apparatus
• How can validity of results be improved


  • Control more variables
  • Use more precise measuring equipment
  • Obtain more results to reduce uncertainty
• What is a random error


  Random errors are caused by unpredictable changes in the investigation, often caused by environmental or irregular changes and can affect precision
• What is a systematic error


  Systematic errors are usually continuous errors throughout the investigation and are usually caused by limitations in equipment, and can affect the accuracy
• What are the S.I base units?


  Mass (Kg) , Length (m) , Time (s) , Current (A) , Temperature (K) , Amount of substance (Mol) , Luminous intensity (Cd)
• What is validity


  A measurement is valid if it measures what it is supposed to be measuring - it is dependent on method and instruments
• What is the true value


  The value that would have been obtained in an ideal measurement
• What is the accepted value


  Our best estimate of the true value
• Control variable


  A variable that must be kept constant to prevent it from affecting the dependent variable
• How to minimise random errors

  To minimise random errors repeat readings and calculate a mean and/or draw a graph
• How to minimise systematic errors

  To minimise a systematic error change your experimental design
• Zero error


  An error that occurs due to the measuring instrument reading a non zero reading when the measured quantity is zero
• How to minimise zero error

  To avoid zero error set a micrometer to zero before opening the jaws, set your balance to zero before measuring a mass
• Resolution


  The smallest measuring interval on an instrument
• What determines the resolution when using a multimeter

  The scale or shunt selected