Choosing a good instrument
When we measure a physical quantity, we want the reading to be as correct as possible. Three important qualities describe how good an instrument is: accuracy, consistency and sensitivity.
- Accuracy is how close a reading is to the true value. An accurate ruler gives a length very near the real length.
- Consistency is how close repeated readings are to one another. A consistent instrument gives almost the same value each time you measure.
- Sensitivity is the ability to detect a small change in the quantity. A sensitive thermometer can show a tiny change in temperature.
Example
A digital balance that shows 2.001 g, 2.000 g and 2.002 g for the same object is very consistent, because the readings are very close to one another.
Errors in measurement
An error is the difference between a measured value and the true value. Errors make readings less accurate, so scientists try to reduce them. Two common types are:
- Parallax error: caused by reading a scale from the wrong angle. Always place your eye directly in front of the scale.
- Zero error: caused when an instrument does not read zero before use. Check and correct the zero first.
Remember
- Accuracy = closeness to the true value.
- Consistency = repeated readings agree with each other.
- Sensitivity = detects small changes.
- Reduce errors by reading correctly and checking for zero error.
To measure well, choose the right instrument, read it at eye level and repeat the measurement to check your result.