Measurement (Cambridge (CIE) IGCSE Physics): Revision Note

Measuring length & volume

• When making measurements in physics, different instruments are used for different measurements

Measuring length

• Rulers can be used to measure small distances of a few centimetres (cm)

  • They are able to measure to the nearest millimetre (mm)

A ruler can measure lengths in cm or mm

• A tape measure is used to measure lengths of tens of centimetres

Measuring volume

• Measuring cylinders are used to measure the volume of liquids

  • By measuring the change in volume, a measuring cylinder can also be used to determine the volume of an irregular shape

Measuring cylinders can be used to determine the volume of a liquid or an irregular shaped solid

Measuring time

• In physics, clocks and digital timers are usually used to measure time intervals

  • Clocks typically measure long time intervals

  • Digital timers, such as stopwatches, typically measure short time intervals

• An important factor when measuring time intervals is human reaction time

  • The standard human reaction time for an alert person is typically around 0.2 to 0.3 s

  • This can have a significant impact upon measurements when the measurements involved are very short 

Multiple readings

• In physics, multiple readings of measurements are often taken to reduce the impact of measurement errors

Taking multiple measurements improves precision and reduces the impact of errors

• The measurement of the thickness of a single sheet of paper is so small that it would be very difficult to get a precise measurement

  • However, measuring the thickness of 100 sheets of paper can be done much more precisely and reduces the uncertainty of the measurement

  • Dividing the answer by 100 then gives a precise figure for the average thickness of one sheet

• Measuring the time period of a simple pendulum would incur a human reaction time error at the start of the measurement and at the end of the measurement

• If the measurement is small, the percentage uncertainty in the measurement is large

• Therefore, multiple readings can be taken to reduce the uncertainty of the measurement

  • The time taken for 10 oscillations of the pendulum can be measured

  • Dividing the answer by 10 gives a more precise figure for the average time taken for one oscillation

• A reference marker can be used when measuring oscillations

  • A reference marker is a visual reference point such as a line or a dot

  • The marker is added to the point at which the measurement is taken, such as the equilibrium position of an oscillating pendulum

  • This makes it easier to see when the pendulum passes this point, reducing the error in starting and stopping the timer