Range & Resolution of Instruments
- All instruments have a range and resolution
- The range is the highest and lowest value an instrument can measure
- The resolution is the smallest increment an instrument can measure
- Examples of resolutions for instruments are:
| Experimental Instrument | Typical Resolution | Typical Range |
| Metre ruler | 1 mm | 0 – 1 m |
| Vernier Calipers | 0.1 mm | 0 – 300 mm |
| Micrometer Screw Gauge | 0.01 mm | 0 – 25 mm |
| Top-pan Balance | 0.01 g | 0 – 1 kg |
| Protractor | 1° | 0 – 180° |
| Stopwatch | 0.01 s | 0 – 9 hours 59 mins 59.99 seconds |
| Thermometer | 1 °C | –10 °C – 110 °C |
| Voltmeter | 1 mV – 0.1 V | 0 – 1000 V |
| Ammeter | 1 mA – 0.1 A | 0 – 10 A |
| Oscilloscope | 1 Hz | 0 – 200 MHz |
- These are just examples of ranges and resolutions for these devices
- For example, some multimeters may have a bigger or smaller range depending on their model
- The resolution of an instrument gives its absolute uncertainty for a digital device
- For an analogue device, such as a thermometer, ruler or pan balance, the uncertainty is ± half the resolution
- This is because when reading between the millimetre scale the measurement will be rounded up or down by eye from the midpoint at 0.5 mm
Worked example
Two digital thermometers display a reading in °C.
Thermometer 1: 80.13 °C
Thermometer 2: 42.0 °C
Which thermometer has the better resolution?
- The resolution is given by the smallest increment that the thermometer can read
- For thermometer 1 this is 0.01 °C
- For thermometer 2 this is 0.1 °C
- Therefore, thermometer 1 has the better resolution
Examiner Tip
Exam questions can refer to different instrument with various ranges and resolutions, for example, ammeters with resolution of 0.2 mA instead. Always use the information given in the question, and look carefully at the scales given. Never just assume the resolution of a piece of instrument given in an exam question.
