• Measurements of quantities are made with the aim of finding the?true value?of that quantity
  • In reality, it is impossible to obtain the true value of any quantity as there will always be a degree of?uncertainty
• The uncertainty is an estimate of the difference between a?measurement reading?and the?true value
• The two types of?measurement errors?that lead to uncertainty are:
  • Random errors
  • Systematic errors

Random Errors

• Random errors cause unpredictable fluctuations in an instrument’s readings as a result of uncontrollable factors, such as environmental conditions
• This affects the?precision?of the measurements taken, causing a wider spread of results about the mean value
• To?reduce?random error:
  • Repeat?measurements several times and calculate an average from them

Systematic Errors

• Systematic errors arise from the use of faulty instruments used or from flaws in the experimental method
• This type of error is repeated consistently every time the instrument is used or the method is followed, which affects the?accuracy?of all readings obtained
• To?reduce?systematic errors:
  • Instruments should be?recalibrated, or different instruments should be used
  • Corrections or adjustments should be made to the technique

Systematic errors on graphs are shown by the offset of the line from the origin

Zero Errors

• This is a type of systematic error which occurs when an instrument gives a reading when the?true reading is zero
  • For example, a top-ban balance that starts at 2 g instead of 0 g

• To?account for?zero errors
  • Take the?difference?of the?offset?from each value
  • For example, if a scale starts at 2 g instead of 0 g, a measurement of 50 g would actually be 50 – 2 = 48 g
  • The offset could be positive or negative

Reading Errors

• When measuring a quantity using an?analogue?device such as a ruler, the uncertainty in that measured quantity is?±0.5 the smallest measuring interval
• When measuring a quantity using a?digital?device such as a digital scale or stopwatch, the uncertainty in that measured quantity is?±1 the smallest measuring interval
• To?reduce?reading errors:
  • Use a?more precise?device with?smaller measuring intervals?and therefore less uncertainty

Both rulers measure the same candy cane, yet Ruler B is more precise than Ruler A due to smaller interval size